For Students of the International Faculty, Specialty «Medicine»

MINISTRY OF HEALTH OF UKRAINE UKRAINIAN MEDICAL STOMATOLOGICAL ACADEMY DEPARTMENT OF HISTOLOGY, CYTOLOGY AND EMBRYOLOGY

"HISTOLOGY, CYTOLOGY AND EMBRYOLOGY" METHODOLOGICAL INSTRUCTIONS MODULE 1 for students of the International faculty, specialty «Medicine» Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Cytology Topic 1 THE SUBJECT OF HISTOLOGY METHODS AND MICROSCOPY Course 1

Faculty Medical The contents of the topic: Medical histology applies microscopy to the human body, seeking to discover the nature of its smaller structures, how they relate to each other, and what they do. Thinking in histology runs along these lines. Histology is colourful. Almost everything seen is actually there; which is not to say that what is not seen is absent. One handles and views actual slides - the source material for most of histology, not just someone else's selected images. The structures can be interpreted as parts in developmental and functional sequences, and be fitted together by satisfying accounts, for example, of how cells defend the body. So much is now known of the roles of cells and structures that histology is both descriptive microanatomy, and an introduction to function for the whole body. Preparation of the Material 1. A major distinction can be drawn between dead and living preparations Dead  Section - a thin slice of tissue or organ - on a glass slide or metal grid.  Smear on a glass slide - suitable for suspensions, e.g., blood, urine, mucus, cyst fluid, bone marrow, etc.  Spread sheet of tissue stretched thin, e.g., areolar connective tissue.  Teased apart fibrous elements, e.g., muscle. Living  Such preparations may be out of the body in a tissue culture system, or living within the body but in an observable situation, e.g., a transparent chamber inserted into the ear or skin.  The first need is to keep the preparation alive. This seriously limits the facilities for observation. For example, staining is usually impracticable. Thus, phase-contrast or dark-field microscopy has to be used in order to overcome the poor contrast between natural structures. 2. Steps needed to make and study a histological section 1. Fixation to prevent post-mortem decomposition, preserve structure, and intensify subsequent staining. 2. (a) Steps involved in imbedding the tissue in a block of wax or plastic, or (b) freezing of the material to a firm mass, for cutting into thin sections on a microtome; 1-150 microns (µm) thick for light microscopy (LM); 30-60 nanometres (nm) for electron microscopy (EM). 3. Units: based on the metre (m): micron/micrometre (µm) = 10-6m; nanometre (nm)/ millimicron (mµ) = 10-9m; Ångström (Å) = 10-10m; 10Å=1nm.

4. Mounting of the section on a glass slide or metal grid. Staining of the section with one or more reagents, e.g., solutions of metallic salts, in one or more stages. 5. For light microscopy, the removal of surplus stain and water, and steps involved in holding a thin glass coverslip to the section with a mounting medium having a refractive index close to that of glass. 6. Observation and recording by means of the microscope, and notes, photomicrography, projection drawing, labelled sketches, counting and reconstructions, digital and videorecording. A drawback to using our eyes as part of the observing instrument is that the visual system does not record accurately. Microscopy 1. Microscopy in general The main distinction is between light microscopy and electron microscopy. The usual light microscope uses a visible light source with a system of condenser lenses to send the light through the object to be examined. The image of this object is then magnified by two sets of lenses, the objective and the eyepiece. Total magnification is then the product of these two lens systems, e.g., 40 X 10 = 400. The resolution or resolving power - how close two structures can be and still be seen as separate - is a measure of the detail that can be seen, and for the light microscope is about 0.25 µm. This limit to resolution is determined mostly by the wavelength of the light; and, however powerful the lens, 0.25 µm cannot be improved upon. The only way to improve resolving power is to reduce substantially the wavelength of the light. This is achieved by the electromagnetic beam of the electron microscope. The beam is focused through the object suspended on its metal grid, and is magnified before striking a fluorescent screen to be transformed into a visible image. The resolutions so far achieved in biology with transmission electron microscopy (TEM/EM) are of the order of 1 nm at a magnification of X 2 000 000. The other forms of microscopy - phase-contrast, interference, fluorescence, confocal scanning, atomic-force (and X-ray diffraction) - will be discussed in , in relation to the problems for which they are suited. 2. Microscopy for the student 1. The usual class microscope has eyepieces/oculars magnifying X 7, and an objective nosepiece carrying X 8, X 20, X 40, and X 90 (oil immersion) lenses. Normally the three lower-power lenses are kept mounted on the nosepiece, whilst the oil immersion objective may be mounted or kept separately. 2. Every time it is used, the microscope should be set up to the best optical advantage. How to do this is described briefly below. 3. Keep in mind the limit to resolution. In practical terms, make special note of those structures that need an oil immersion lens to be seen or are visible only in electron microscopy.

4. The section has some thickness, so that the fine-focusing adjustment should be used continually during observation to bring out fine detail, e.g., cilia on cells. Essentially, though, we are getting a two-dimensional picture from an originally three-dimensional piece of material. For what the structure looked like in the third dimension, the student can try to reconstruct mentally what is going on in the missing dimension, and look up views of the structure in scanning electron microscopy. 5. Artefacts (appearances not due to the original nature of the material as obtained from the body) can arise at all stages in the treatment of the section. Gross examples arise from: (1) clumsy excision from the body; (2) poor or inappropriate fixation; (3) shrinkage and, worse, uneven shrinkage, leading to artificial spaces and distorted relations; (4) cutting scores from a bad microtome knife; (5) the section not flat on the slide; (6) water, dirt or bubbles on or in the section; (7) dirt on the microscope lenses; (8) patchy or faded staining; unbalanced staining when more than one stain has been applied; (9) precipitate from fixative or stain; (10) tears and folds in the section. 6. Setting up the microscope – see in the album. 3. Differences between light and electron microscopy 1. Table 1 gives some differences between the two approaches. The detailed morphology revealed by EM may be called fine or submicroscopic structure/ultrastructure. 2. The direct comparison of LM and EM images of a structure requires that the magnifications be of the same order. Noting the magnification, on the 'scope or in the figure legend, allows one to adjust one's expectations of what may be seen, and should always be done. 3. A growing practice in histology and pathology is to fix and prepare the tissue by EM standards, imbed in plastic and cut semi-thin (1 µm) sections for staining by modified LM methods. LM then reveals good cellular detail and fewer artefacts. 4. Two other techniques yield anatomical images - fibre-optic endoscopy and scanning EM - are being digested by the anatomical texts. Endoscopy from its low magnification is marginal to histology, but related in that endoscopy is used to obtain biopsy specimens for histopathology. SEM strengthens one's conception of microscopic structures, e.g., cilia, renal podocytes, bone under resorption, and effectively counters the unavoidable impression of structures existing only in two dimensions. Table 1. Some differences between light and electron microscopy. Light microscopy Electron microscopy Image is presented directly to the eye. Image is in shades of green on the screen; Image keeps the colours given the photographically, only in black and specimen by staining. white. Modest magnification to X 1500; but a High magnification, up to X 2,000,000 wider field of view and easier thus the range of magnification is greater. orientation. 3

Resolving power to 0.25 µm. Resolving power to 1 nm (0.001µm.) Frozen sections can yield an image Processing of tissue takes a day at least. within 20 minutes. High resolution and magnification Crude techniques of preparation demand good fixation (e.g. by vascular introduce many artefacts. perfusion), cleanliness and careful (Histochemical methods are better.) cutting, adding up to fewer artefacts. Very thin sections provide no depth of Section thickness (1-30 µm) gives a focus, but 3-D information can be had little depth for focus for appreciation of from: (a) thicker sections by high voltage the third dimension. Serial sections can EM; (b) shadowed replicas of fractured be cut, viewed and used to build a surfaces; (c) scanning electron composite image or representation. microscopy (SEM). Heavy metal staining gives a more Most materials and structures cannot be comprehensive picture of membranes, stained and viewed at the same time; granules, filaments, crystals, etc.; but this stains are used selectively to give a view is incomplete and even visible partial picture, e.g. a stain for mucus bodies can be improved by varying the counterstained to show cell nuclei. technique. Specimen is in vacuo. Its small size Specimen can be large and even alive. creates more problems with sampling and orientation.

Dynamic nature of the cell. The cell is not a static entity in life. Its chemical constitution and morphology are in continuous flux. Its complement of organelles is altering, with wearing-out and replacement, i.e., the cell is having to synthesize its own material. The cell itself represents a system of activities isolated to partial extent from an extracellular environment. Within the cell things are constantly being altered, moved around and joined up within the membranes. The membranes define temporary compartments separated from the cytoplasm, where particular activities can be confined and controlled by enzymes attached to the extensive membrane surfaces. Dynamic aspects of the cell's existence are partly deduced from a study of its morphology in specimens fixed in various states, partly from microscopical observations of living cells, and from histophysiological experiments outlined in. ➢ Biological tissues must undergo a series of treatments to be observed with light and electron microscopes. The process begins by stabilization of the tissue with chemical fixatives. Next, the tissue is made rigid to allow sectioning. Finally, it is stained to provide contrast for visualization in the microscope. ➢ Steps in tissue preparation 1. Fixation 2. Dehydration

3. Infiltration and embedding 4. Sectioning 5. Staining 6. Chemical Fixation ➢ Preserves cellular structure and maintains the distribution of organelles. ➢ Formaldehyde and glutaraldehyde are the most commonly used chemical fixatives. They stabilize protein by forming cross-links between primary amino groups. Formaldehyde in solution is referred to as formalin. ➢ Osmium tetraoxide is a fixative used to preserve lipids, which aldehydes cannot do. Osmium combines with and stabilizes lipid and, in addition, also adds a brown color (light microscopy) or electron density (electron microscopy) at the site of the lipid. Osmium fixation is required for electron microscopy, especially to preserve the lipid in membranes. DEHYDRATION, INFILTRATION, AND EMBEDDING ➢ Tissue water is not miscible with the embedding solutions and must be replaced using a series of alcohols at increasingly higher concentrations. This step is followed by alcohol replacement with an intermediate solvent that is miscible with both alcohol and the embedding solutions. ➢ Infiltration and embedding. The liquid form of the embedding compound, for example, paraffin wax or epoxy plastic, replaces the intermediate solvent. The liquid embedding medium is allowed to solidify, thereby providing rigidity to the tissue for sectioning. Sectioning ➢ The embedded tissue is cut thin enough to allow a beam of light or electrons to pass through. ➢ Section thickness  Light microscopy. 1–20 microns  Electron microscopy. 60–100 nanometers ➢ Section planes 1. Cross-section (cs) or tranverse section (ts) is a section that passed perpendicular to the long axis of a structure. 2. Longitudinal section (ls) is a section that passed parallel to the long axis of a structure. 3. Oblique (tangential) section is any section other than a cross- or longitudinal section. STAINING ➢ Most tissues have no inherent contrast; thus, stains must be applied to visualize structures. ➢ Conventional staining. Relies mostly on charge interactions.

1.Light microscopy  Hematoxylin and eosin (H&E). These two dyes are the most commonly used stains in routine histology and pathology slides. Most conventional stains bind to tissue elements based on charge interactions, that is, positive charge attraction for a negatively charged structure. Hematoxylin binds to negatively charged components of tissue, the most prominent being nucleic acids. Hematoxylin imparts a purple/blue color to structures and, therefore, the nucleus and accumulations of rough endoplasmic reticulum in the cytoplasm, which contains large amounts of nucleic acid, appear blue or purple in sections.  Structures, like the nucleus and rough endoplasmic reticulum that stain with hematoxylin, are referred to as basophilic or “base loving.” The term basophilia, refers to the property of a structure or region that stains with a basic dye, such as hematoxylin. Structures that stain with eosin, for example, the cytoplasm of most cells and collagen fibers, appear pink or orange and are referred to as eosinophilic. 2.Electron microscopy  Images in the electron microscope are produced by passing a beam of electrons though the tissue that has been “stained” with salts of heavy metals, usually lead (lead citrate) and uranium (uranyl acetate). These metals bind to areas of negative charge and block the passage of the electrons through the section, resulting in a dark area in the electron micrograph. Electron density is also achieved using osmium tetroxide, which also serves as a lipid fixative.  Areas or structures in tissue that bind the metals are referred to as electron dense. Areas where the metals do not bind appear light and are referred to electron lucent. ➢ Histochemical staining. Localizes chemical groups  Osmium tetroxide. Stains lipids  Periodic acid–Schiff stain (PAS). Stains carbohydrates Staining Reactions Staining reactions have both physical and chemical characteristics. The mechanisms involved in staining include the following: The dye may actually be dissolved in the stained substance. Most fat staining is accomplished in this fashion. A dye may be absorbed on the surface of a structure, or dyes may be precipitated within the structure, simply because environmental factors (pH, ionic strength, temperature, etc.) favor absorption or precipitation. Most staining reactions involve a chemical union between dye and stained substance through salt linkages, hydrogen bonds, or others. Staining with these dyes results in a predictable color pattern based in part on the acid base characteristics of the tissue. However, color and color distribution are not absolutely reliable for discrimination between tissue components. Color will vary not only with specific stains used, but also with the conditions that exist during

6 preparation of the slide. These include everything from the initial fixing solution to the ionic strength of the staining solution and the differentiating solvents utilized after staining. Acid and Basic Dyes Most histologic dyes are classified either as acid or as basic dyes. An acid dye exists as an anion (negatively charged) in solution, while a basic dye exists as a cation (positive charge). For instance, in the hematoxylin-eosin stain (H&E), the hematoxylin-metal complex acts as a basic dye. The eosin acts as an acid dye. Any substance that is stained by the basic dye is considered to be basophilic; it carries acid groups which bind the basic dye through salt linkages. When using hematoxylin, basophilic structures in the tissue appear blue (or purple or brown; this varies according to the stain that is being used). A substance that is stained by an acid dye is referred to as acidophilic; it carries basic groups which bind the acid dye. With eosin, acidophilic structures appear in various shades of pink. Since eosin is a widely used acid dye, acidophilic substances are frequently referred to as eosinophilic. Trichrome Stains In the trichrome stains, which commonly employ more than one acid dye, use is made of dye competition. For instance, acid fuchsin and picric acid are used in Van Gieson's trichrome stain. In the picric acid-fuchsin mixture, the small picric acid molecule reaches and stains the available sites in muscle before the larger fuchsin molecules can enter. Used by itself, acid fuchsin has no difficulty in staining muscle. Neutral Stains These are compounds of an acid dye and basic dye. For instance, aqueous solutions of acid fuchsin may be neutralized by addition of aqueous methyl green. The resulting neutral product is water insoluble, but may be kept in solution by the presence of excess amounts of either component. The tissue stained with such a solution may show affinity for the acid dye, the basic dye, and for the whole compound. Some blood stains are "neutral stains." Wright's Stain, for instance, is formed by the combination of partially oxidized and demethylated methylene blue and eosin. Such a stain can be used to differentiate between blood cells that contain acidic, basic, and neutral granules. Hematoxyl and Eosin (H&E) This is a good general stain and is widely used. Most of your slides are stained with H&E. A hematoxylin-metal complex acts a as a basic dye, staining nucleic acids in the nucleus and the cytoplasm blue, brown, or black. Eosin is an acid aniline dye which stains the more basic proteins within cells (cytoplasm) and in extracellular spaces (collagen) pink to red. Cartilage and mucus may stain light blue. Masson Trichrome Stain A staining sequence involving iron hematoxylin, acid fuchsin, and light green. It is a good stain for distinguishing cellular from extracellular components. Collagen fibers stain an intense green. Black or brown nuclei; mucus and ground substances

7 take on varying shades of green. Cytoplasm stains red. Elastic fibrils, red blood cells and nucleoli stain pink. Aldehyde Fuchsin Stains elastic fibers purple to black. Can be counter-stained with a dye of contrasting color, such as metanil yellow. Verhoeff's Hematoxylin Another variant of the versatile hematoxylin stains. This method stains elastic fibers black in addition to nuclei. Reticular Fiber Stain – Weigert Reticular fibers are impregnated with a silver salt and appear as sharp black. Collagenous fibers usually stain purple. This stain can be used with a counterstain or without, if the silver stain turned out very dark. Wright's/Giemsa Stain This and similar stains for blood and bone marrow smears are mixtures of basic (methylene blue derivatives) and acid dyes (usually eosin). According to the number of acid and basic groups present, cell components take up the dyes from the mixture in various proportions. Some blood stains use acid and basic dyes in separate dye baths. Metachromatic Stain Certain basic dyes, such as toluidine blue, stain nucleic acids blue (the orthochromatic color), but sulfated polysaccharides purple (the metachromatic color). When dye molecules bound to sulfate groups are stacked closely together, the dye experiences a color shift from blue to purple. Thus, a metachromatic reaction often indicates the presence of numerous closely packed sulfate groups. Plastic Sections Stained with Toluidine Blue or with H&E Plastic embedded tissues can be cut as thin as 0.1 um with a glass knife. These sections are then stained with toluidine blue in an alkaline solution. Almost all tissue components are stained more or less deeply (usually a bluish-purple) and structural detail is very sharp. For the knowledgeable observer, this type of preparation may be very informative. Periodic Acid Schiff (PAS) Adjacent hydroxyl groups (1, 2 glycols) or amino and hydroxyl groups are oxidized to aldehyde groups with periodic acid. Schiff's Reagent then produces a red or magenta addition product with the aldehyde groups and this technique identifies a number of polysaccharides and carbohydrate-containing compounds. The slide may also be counter stained with hematoxylin. Feulgen Reaction: Mild hydrolysis with HCl frees the aldehyde group of deoxyribose, which is then reacted with the Schiff's reagent. This reaction is highly specific for DNA and may also be used with a counter stain for the cytoplasm. ➢ Immunocytochemistry. Localization of specific antigens in cells using labeled antibodies ➢ In situ hybridization. Detection of messenger RNA or genomic DNA sequences using labeled nucleotide probes

ARTIFACT ➢ The term artifact is used to refer to any feature of a tissue section that is present as a result of the tissue processing. These include tears and folds, shrinkage, spaces resulting from extracted cellular contents (e.g., lipid, precipitates), and redistributed organelles. MICROSCOPY ➢ Properties 1.Resolution is the smallest degree of separation at which two objects can still be distinguished as separate objects and is based on the wavelength of the illumination.  Light microscopy. Approximately 200nm  Electron microscopy. Approximately 1nm 2.Magnification. Enlargement of the image ➢ Bright field microscope  An image is formed by passing a beam of light through the specimen and then focusing the beam using glass lenses.  The bright field microscope is called a compound microscope because it uses two lenses, objective and ocular, to form and magnify the image. The compound microscope typically has a total magnification range of 40–1000 times. ➢ Electron microscope 1.Transmission electron microscope (TEM)  An image is formed by passing a beam of electrons through the specimen and focusing the beam using electromagnetic lenses.  Similar arrangement of lenses is used as with optical microscopy; magnification is up to 400,000 times, which is sufficient to visualize macromolecules (e.g., antibodies and DNA). 2.Scanning electron microscope (SEM). The image is formed by electrons that are reflected off the surface of a specimen, providing a three-dimensional image; magnification ranges from 1–1000 times. ➢ Freeze fracture technique  This technique is used to examine the number, size, and distribution of membrane proteins.  A tissue is frozen and mechanically fractured; the exposed membrane surface is coated with a thin metal film called a “replica.”  The replica is viewed by TEM. Membrane proteins appear either as bumps or pits in the replica. SECTION INTERPRETATION ➢ In histology, three-dimensional tissues are viewed in two dimensions; therefore, it is extremely important to learn to visualize the threedimensional structure from the two-dimensional image. For example, a cross-section through a tubular 9 structure appears as a ring, whereas a longitudinal section appears as two parallel bands. As an added challenge, most sections pass obliquely to these perpendicular axes and, thus, require further “mental gymnastics.” UNITS OF MEASURE ➢ Millimeter (mm) = 1/1000 meter, 10-3M ➢ Micron, micrometer (mm) = 1/1000mm, 10-3mm, 10-6M ➢ Nanometer (nm) = 1/1000mm, 10-3mm, 10-9M ➢ Еngstrцm unit (Е) = 1/10nm, 10-10M

Cytological description of an individual cell. In light microscopy involves: (1) relative and absolute size; (2) shape; (3) number of nuclei; (4) shape and size of nucleus/nuclei; (5) intensity of nuclear staining; (6) amount of cytoplasm; (7) staining affinity of cytoplasm, e.g., basophilic, acidophilic (eosin), argentophilic (silver stains), or chromophobe (liking no stain); (8) granular cytoplasm; (9) nature of any inclusions, for instance, melanin pigment, fat, carbon, bacteria, zymogen granules, glycogen, mucus; (10) specializations of the cell membrane, e.g., cilia, a brush/striated border (many microvilli); (11) distinctive organelles in cytoplasm and their position, e.g., prominent Golgi complex, many fibrils, numerous orderly mitochondria giving another striated effect, Nissl substance (GER) in nerve cells; (12) whether the cell is in some phase of mitosis or meiosis; (13) the cell's surroundings; (14) manifest properties of the living cell, e.g., motility, phagocytosis, contractility.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Cytology Topic 2 CELLS. PLASMALEMMA. CELL JUNCTIONS Course 1

Faculty Medical The contents of the topic: 1. Body components The human body content of the cells, tissues, organs and organ’s systems. These are cells, extracellular substances, and body fluids. Fluids can have their suspended solid constituents viewed microscopically as smear preparations (see Blood), but are otherwise of limited histological interest. Extracellular substances are important for the cells whose environment they form: they reflect and help control cellular activities, aside from their critical structural mechanical properties. Individual materials can be seen and localised by histochemistry. 2. Cells: chemical constitution and fixation 1. Composition: much water; proteins, nucleic acids, lipids, carbohydrates, amino acids, minerals, hormones, vitamins, etc. 2. Fixation stabilizes mainly proteins, and protein conjugates. These substances are used as building materials for the firmer structures of the cell. Lipids, minerals, glucose, and smaller molecules are usually lost from the section during processing. What is left is a skeleton of structures - membranes, granules, filaments - made up of proteins, polypeptides, polysaccharides and some other macromolecular materials. The special steps of histo- and cytochemistry serve and reveal some smaller molecules.

3. Cells: living properties and specialization 1. Properties of cells: (a) general - communication, respiration and energy storage and release, synthesis, excretion, growth, differentiation, reproduction; (b) specialized - irritability to stimuli (excitability), motility, contractility, conductivity, absorption, phagocytosis, secretion. 2. During development from the fertilized oocyte, a great variety of cells is formed in the mammal, each kind specializing in a certain function, e.g., secretion, but many activities, such as energy production, are common to all cells. The cells of the four primary tissues - epithelial, connective, nervous and muscular - are divided along lines of specialized function, e.g., muscle for contractility and excitability. 4. Cell morphology 1. Cells performing a given function have a characteristic size, form and fine structure adapted to that task. However it may help at this stage to think in terms of a composite cell having all the features the various cells of the body display. 2. The cell is defined as a distinct entity by having a thin skin or plasmalemma/cell membrane separating off from the outside a soft, viscous, almost fluid cytoplasm, in which are suspended a number of firmer, recognizable structures - organelles and inclusions - and one or more nuclei. The nucleus, likewise, is a mass of material enclosed in nuclear membranes. 5. Cell components – cytoplasm, plasmalemma and nucleus. 1.Cytoplasm. It consist of organelles, includings and hyaloplasm - the so-called soluble phase of the cell, consisting mostly of water, dissolved solutes, and larger molecules in suspension tending to link repetitively with covalent bonds giving the cytoplasm a dense, viscous colloidal sol or gel consistency. 2.Cell or plasma membrane/plasmalemma o Made of unit membrane roughly 7.5 nm wide; in the EM picture with appropriate fixation it has a trilaminar appearance of two dark bands with a light layer betwen them; the light layer is mostly non-polar lipid, the dark layers mostly the charged ends of the lipid molecules with attached protein. o A coat of glycoproteins (sugars+protein) - glycocalyx - adheres to the outside of most cells – undermembranous complex. o The plasma membrane is flexible, semi-permeable, and experiences active transport and potential differences across it. o By the cell membrane's fusing with the intracellular membrane around stored material, then breaking open at a point along the line of fusion the material can be released to outside the cell - exocytosis/emiocytosis. By bringing extracellular things into an invagination, followed by selective membrane fusion and separation, materials are brought into the cell - endocytosis: phagocytosis for solids, pinocytosis for fluids; endocytosis includes these bulk movements, but also signifies the internalization of membrane receptors and bound ligands on a smaller scale.

o Specializations of form shown by the plasma membrane include: microvilli, cilia with basal bodies, (iii) pinocytotic vesicles/pinosomes/caveolae intracellulares, infoldings or plications, desmosomes, gap junctions/nexuses, occluding junctions, stereocilia (long microvilli). o Some vesicles involved in transport into the cell have prominent coats of clathrin attached to the membrane. o Proteins of internal surface of the plasmalemma form the cytoskeleton(submembranous complex) 3.Cell nucleus consist of Nuclear membrane, Chromatin, Nucleoplasma and Nucleola.

6. Cell Membranes I. Functions of the membrane are: 1. Separation the cell from the external enviropment. 2. Firm attachment to other cells or a basal lamina; membrane specializations for this are: junctional complexes, gap junctions/ nexuses, desmosomes, hemidesmosomes, intercalated discs, and membrane interdigitations. 3. Transport of materials in and out of the cell served by: permeability (selective) of the membrane, active transport through the membrane, endocytosis, and its more scaled up forms - pinocytosis and phagocytosis, exocytosis; and increased exchange surface area by microvilli (thousands on a cell), and infoldings of membrane. 4. Movement of the cell itself by pseudopodial, filipodial, or lamellipodial extensions (think karate: fist, finger, or side of the hand) and the release of any firm attachments, or by flagellate activity, e.g., by sperm. (Microspikes and ruffles are alternative names for filopodia and lamellipodia, respectively.) 5. Movement of materials outside the cell by the activity of cilia, e.g., ciliated epithelia of the respiratory tract and uterine tube. The wide-spread occurrence of solitary cilia (flagella), e.g., on neurons, adrenal cells, smooth muscle, may involve a vestigial body or one still functional. The stereocilia

of the male reproductive tract are non-motile, clumped, long microvilli, probably absorptive. 6. Communication and transduction. Each cell collaborates with both adjacent cells, and those of the whole body, for development, growth, homeostasis, regeneration, and its own particular task. The importance of the cell membrane in receiving and sending the necessary signals is stressed by the number of examples given: . The binding of hormones to receptors on the membrane. . The binding of the lymphocyte's membrane receptor to an antigen. . Transmitter chemicals depolarize neurons and muscle cells. . Excitable tissues propagate action potentials along the membranes. . Schwann cells wrap their membranes many times round an axon's to make myelin sheath segments for faster signalling. . Chemical stimuli are transduced into nerve impulses in chemoreceptors; mechanical stimuli in mechanoreceptors. . Gap junctions permit ions and excitation to spread from cell to cell, and unify and synchronise actions of many cells/cell assemblies. . In development, epithelial and mesenchymal cells interact in sequence to induce cell differentiations, e.g., in tooth and glands. . Cells attract and fuse with one another to form multinucleated cells, e.g., skeletal muscle and osteoclasts. . Chemotactic agents act on phagocytic cells to attract them to their targets. . Keratinocytes of the skin phagocytose melanin pigment offered to them in the processes of melanocytes. . Macrophages detect spent or abnormal red blood cells, and hold and engulf either the whole cell, or the part holding an unwanted body. II. Molecules Wherever such actions are described, special molecules are acting, by binding to each other, changing their conformation, or some other means. o Spectrin/fodrin provides a subplasmalemmal skeleton attached to the cell membrane by ankyrin, and to actin of the cytoskeleton, to permit control of the membrane's shape and movement. o Cell adhesion molecules (CAMs) allow cells to attach to only certain cell types. o Integrins are cell-surface-membrane dimeric molecules (an alpha with a beta), by which cells choose to which extracellular matrix (ECM) components they wish to fasten, e.g., laminin. o Connexins are proteins that combine as hexamers to form connexons - the gap-junction channels, allowing ions and small molecules to pass between cells. Connexins and the transports allowed vary among liver cells, neurons. o Occludins are responsible for the seal preventing passage of materials past inter-epithelial tight junctions. 7. Basic Membrane structure

The proteins of the membrane are: integrals, semi-integrals (external and internal) and peripheral (external and internal). o They may form are esssential part of the structure of the membrane i.e., they may be structural proteins. o Some proteins play a vital role in transport across the membrane and act as pumps. Ions get attached to the protein on one surface and move with the protein to the other surface. o Some proteins are so shaped that they form passive channels through which substances can diffuse through the membrane. However, these channels can be closed by a change in the shape of the protein. o Other proteins act as receptors for specific hormones or neurotransmitters. o Some proteins act as enzymes. 8. Contacts between adjoining cells In tissues in which cells are closely packed the cell membranes of adjoining cells are separated, over most of their extent by a narrow space (about 20 nm). This contact is sufficient to bind cells loosely together, and also allows some degree of movement of individual cells. In some regions the cell membranes of adjoining cells come into more intimate contact: these areas are marked by structural specializations as described below. Zonula Occludens At such a junction the two plasma membranes are in actual contact. These junctions act as barriers that prevent the movement of molecules into the intercellular spaces. For example, intestinal contents are prevented by them from permeating into the intercellular spaces between the lining cells. Zonulae occludens are, therefore, also called tight junctions. Apart from epithelial cells, zonulae occludens are also present between endothelial cells. In some situations

15 occlusion of the gaps between the adjoining cells maybe incomplete and the junction may allow slow diffusion of molecules across it. These are referred to as leaky tight junctions.

Desmosomes (Maculae Adherens) This is the most common type of junction between adjoining cells. A desmosome is a small circumscribed area of attachment. At the site of a desmosome the plasma membrane (of the cell) is thickened because of the presence of a dense layer of protein on its inner surface (i.e., the surface towards the cytoplasm). The thickened areas of the two sides are separated by a gap of 20 nm or more. The region of the gap is rich in a glycoprotein called desmoglea. The thickened areas of the two membranes are held together by fibrils that appear to pass from one membrane to the other across the gap. Closer examination shows, however, that the fibrils do not pass from one cell to the other. Instead the fibrils of each side are in the form of loops: the loops of the opposing membranes interlock. The cytoplasmic aspect of the thickened areas of the cell membrane also gives attachment to numerous fibrils that pass into the cytoplasm. Desmosomes are present where strong anchorage between cells is needed. Zonula Adherens In some situations, most typically near the apices of epithelial cells, we see a kind of junction called the zonula adherens. This is similar to a desmosome in being marked by thickenings of the two plasma membranes, to the cytoplasmic aspects of which fibrils are attached. However, the junction differs from a desmosome in that instead of being a small circumscribed area of attachment the junction is in the form of a continuous band around the apical part of the epithelial cell; and in that the gap between the thickenings of the plasma membranes of the two cells is not traversed by filaments. An adhesive material is probably present in this situation. Apart from epithelial cells zonulae adherens are also seen between smooth muscle cells, and between myocytes of cardiac muscle in the region of intercalated discs. Gap Junctions (Nexuses) At these junctions the plasma membranes are not in actual contact (as in a tight

16 junction), but lie very close to each other, the gap being reduced (from the normal 20 nm) to 3 nm. Placed in this gap there are bead-like structures arranged in the form of hexagons. A minute canaliculus passing through each 'bead' connects the cytoplasm of the two cells thus allowing the free passage of substances from one cell to the other. Gap junctions are, therefore, also called maculae comnumicantes. They are widely distributed in the body. Junctional Complex Near the apices of epithelial cells the three types of junctions described above, namely zonula occludens, zonula adherens and macula adherens are often seen arranged in that order. They collectively form a junctional complex. Stem cells. For a stable population, the corollary to cell death is cell renewal. This requires: o the proliferation of cells; o an enduring population of stem cells; o controls (+ & -) that promote division of stem cells to maintain their numbers - self-replication; o controls that cause differentiation of certain of the stem cells to become the determined/committed precursors of the mature cells of the tissue; o factors to promote division of the precursors/progenitors and their further differentiation. The controlling factors include cytokines. More is known about the ensuing progenitor cells than about the stem cells. Although not essential to the concept of stem cells, at step (iv) above, stem cells usually give rise to more than one lineage of differentiated cells, in order to furnish the needed diversity of cell types in blood and most epithelia.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Cytology Topic 3 ORGANELLES AND INCLUSION Course 1

Faculty Medical The contents of the topic: The cytoplasm of a typical eukaryotic cell contains various structures that are referred to as organelles. They include the membrane-bound and the non- membranous organelles. Other components of cytoplasm are gialoplasm and inclusions. Mitochondria Mitochondria can be seen with the light microscope in specially stained preparations. They are so called because they appear either as granules or as rods (mitos = granule; chondrium = rod). The number of mitochondria varies from cell to cell being greatest in cells with high metabolic activity (e.g., in secretory cells). Mitochondria vary in size, most of them being 0.5 to 2μm in length. The mitochondrion is bounded by a smooth outer membrane within which there is an inner membrane. The inner membrane is highly folded on itself forming incomplete partitions called cristae. The space bounded by the inner membrane is filled by a granular material called the matrix. This matrix contains numerous enzymes. It also contains some RNA and DNA: these are believed to carry information that enables mitochondria to duplicate themselves during cell division. An interesting fact, discovered recently, is that all mitochondria are derived from those in the fertilized ovum, and are entirely of maternal origin.

Mitochondria are of great functional importance. They contain many enzymes including some that play an important part in Kreb's cycle. ATP and GTP are formed in mitochondria from where they pass to other parts of the cell and provide energy for various cellular functions. These facts can be correlated with the observation that within cell mitochondria tend to concentrate in regions where 18 energy requirements are greatest. The enzymes of Kreb's cycle are located in the matrix, while enzymes associated with the cytochrome system are present on the inner mitochondrial membrane. Mitochondria are also concerned with fatty acid metabolism, and various other chemical reactions. Endoplasmic Reticulum The cytoplasm of most cells content with com of membranes that constitute the endoplasmic reticulum. The membranes form the boundaries of channels that may be arranged in the form of flattened sacs (or cistern) or of tubules. Because of the presence of the endoplasmic reticulum the cytoplasm is divided into two components, one within the channels and one outside them.

In most places the membranes forming the endoplasmic reticulum are studded with minute particles of RNA called ribosomes. The presence of these ribosomes gives the membrane a rough appearance. Membranes of this type form what is called the rough (or granular) endoplasmic reticulum. In contrast some membranes are devoid of ribosomes and constitute the smooth or agranular endoplasmic reticulum. Rough endoplasmic reticulum represents the site at which proteins are synthesized. The attached ribosomes play an important role in this process. Smooth endoplasmic reliculum is associated with numerous biochemical processes including carbohydrate metabolism. Products synthesized by the endoplasmic reticulum are stored in the channels within the reticulum. Ribosomes, and enzymes, are present on the 'outer' surfaces of the membranes of the reticulum. Golgi Complex The Golgi complex (or Golgi apparatus) can be seen as a small structure of irregular shape, usually present near the nucleus. When examined with the EM the complex is seen to be made up of membranes similar to those of smooth endoplasmic reticulum. The membranes form the walls of a number of flattened sacs that are stacked over one another. Towards their margins the sacs are continuous with small rounded vesicles. The Golgi complex is intimately connected with the formation of several secretory products, specially those containing carbohydrates.

The protein component of these products is synthesized in rough endoplasmic reticulum. As the proteins pass through successive sacs of the Golgi complex they undergo a process of purification. In the Golgi complex carbohydrates are added to the proteins to form protein-carbohydrate complexes. These complexes are formed within the cisternae of the Golgi apparatus. They pass to the margins of the cisternae where they separate from the Golgi complex forming membrane bound secretory vacuoles.The membranes of the Golgi complex give attachment to enzymes associated with carbohydrate synthesis. Lysosomes may also be produced in the Golgi complex. Lysosomes These vesicles (primary, secondary, rest bodies and autophagosomes) contain enzymes that can destroy unwanted material present within a cell. Such material may have been taken into the cell from outside (e.g., bacteria); or may represent organelles that are no longer of use to the cell. The enzymes present in lysosomcs include proteases, Lipases, curbohydrases, and acid phosphatase. (As many as 40 different lysosomal enzymes have been identify. Passing along the channel of the reticulum they reach the Golgi complex. Here the enzymes come to be surrounded by membranes and are set free into the cyloplasm in the form of vesicles that bud off from marginal areas of the Golgi complex.

Lysosomes help in 'digesting' the material within phagosomes (described above) as follows. A lysosome, containing appropriate enzymes, fasts with the phagosome so that the enzymes of the former can act on the material within the phagosome. These bodies consisting of fused phagosomes and lysosomes arc refried to a secondary lysosomes or phagolysosomes. In a similar manner lysosomes may also fuse with pinocytotic vesicles. The structures formed by such fusion often appear to have numerous small vesicles within them and called multivesicular bodies. After the material in phagosomes or pinocytotic vesicles has been 'digested' by lysosomes, some waste material may be left. Some of it is thrown out of the cell by exocytosis. However, some material may remain within the cell in the form of membrane bound residual bodies. Lysosomal enzymes play an important role in the destruction of bacteria phagocytosed by the cell. Lysosomal enzymes may also be discharged out of the cell and may influence adjoining structures. Lysosomes are present in all cells except mature erythrocytes. They are a prominent feature in neutrophil leucocytes. Ribosomes We have seen above that ribosomes are present in relation to rough endoplasmic reticulum. They may also lie free in the cytoplasm. They may be present singly in which case they are called monosomes; or in groups which are referred to as potyribosomes (or polysomes). Each ribosome consists of proteins and RNA (ribonucleic acid) and is about 15 nm in diameter. The ribosome is made up of two subunits one of which is larger than the other. Ribosomes play an essential role in protein synthesis.

Microfilaments & Microtubules The cytoplasm of many varieties of cells contains thin elongated elements. Some of these are tubular, and are circular in cross section: they are called microtubules. Others, called micro filaments, are solid fibres. These elements can be made out in light microscopic preparations of dividing cells in which they form the mitotic spindle. With the EM they can be identified in many other cells and the distinction between tubule and filaments can also be made out. Microtubules and microfilaments (along with some other filaments present in the cytoplasm) constitute the cytoskeleton.

Both microtubules and microfilaments are made up of proteins. The proteins forming microtubules are called tubulins. Microfilaments are usually composed of a protein called actin, but in some situations (e.g., in neurons) they may be composed of other proteins. A microtubule is about 24 nm in diameter. A microfilament is 6-8 nm in diameter. Intermediate filaments about 10 nm in diameter are found in many cells where structural strength is required: these include nerve cells (in which they are seen as neurofilaments), epithelial cells and neuroglial cells.

Centrioles All cells capable of division (and even some which do not divide) contain a pair of structures called centrioles. With the light microscope the two centrioles are seen as dots embedded in a region of dense cytoplasm which is called the centrosome. With the EM the centrioles are seen to be short cylinders that lie at right angles to each other. When we examine a transverse section across a centrioles (by EM) it is seen to consist essentially of a series of microtubules arranged in a circle. There are nine groups of tubules each group consisting of three tubules. Centrioles play an important role in the formation of various cellular structures that are made up of microtubules. These include the mitotic spindles of dividing cells, cilia, flagella, and some projections of specialized cells (e.g., the axial filaments of spermatozoa). It is of interest to note that cilia, flagella and the tails of spermatozoa all have the 9+2 configuration of microtubules that are seen in centrioles. SPETIAL ORGANELLES Many cells show projections from the cell surface. The various types of projections are described below. Cilia These can be seen, with the light microscope, as minute hair-like projections from the free surfaces of some epithelial cells. In the living animal cilia can be seen to be motile. Details of their structure, described below, can be made out only by EM. The free part of each cilium is called the shaft. The region of attachment of the shaft to the cell surface is called the base (also called the basal body, basal granule, or kinetosome). The free end of the shaft tapers to a tip. In structure the cilium consists of an outer covering which is formed by an extension of the cell membrane; and an inner core that is formed by microtubules arranged in a definite manner. It has a striking similarity to the structure of a centriole (described above). There is a central pair of tubules which is surrounded by nine pairs of tubules. The outer tubules are connected to the inner pair by radial structures (which are like the spokes of a wheel). Other projections pass outwards from the outer tubules. As the tubules of the shaft are traced towards the tip of the cilium it is seen that one tubule of each outer pair ends short of the tip so that near the tip each outer pair is represented by one tubule only. Just near the tip, only the central pair of tubules is seen. At the base of the 23 cilium one additional tubule is added to each outer pair so that here the nine outer groups of tubules have three tubules each, exactly as in the centriole. Functional significance of cilia The cilia lining an epithelial surface move in coordination with one another the total effect being that like a wave. As a result fluid, mucous, or small solid objects lying on the epithelium can be caused to move in a specific direction. Movements of cilia lining the respiratory epithelium help to move secretions in the trachea and bronchi towards the pharynx. Ciliary action helps in the movement of ova through the uterine tube, and of spermatozoa through the male genital tract. In some situations there are cilia-like structures that perform a sensory function. They may be non-motile, but can be bent by external influences. Such 'cilia' present on the cells in the olfactory mucosa of the nose are called olfactory cilia: they are receptors for smell. Similar structures called kinocilia are present in some parts of the internal ear. In some regions there are hair-like projections called stereocilia: these are not cilia at ah1, but are large microvilli. Flagella These are somewhat larger processes having the same basic structure as cilia. In the human body the best example of a flagellum is the tail of the spermatozoon. The movements of flagella are different from those of cilia. In a flagellum movement starts at its base. The segment nearest the base bends in one direction. This is followed by bending of succeeding segments in opposite directions so that a wave like motion passes down the flagellum. When a spermatozoon is suspended in a fluid medium this wave of movement propels the spermatozoon forwards (exactly in the way a snake moves forwards by a wavy movement of its body). Microvilli These are finger-like projections from the cell surface that can be seen only with the EM. Each microvillus consists of an outer covering of plasma membrane and a cytoplasmic core in which there are numerous microfilaments. Numerous enzymes have been located in microvilli. With the light microscope the free borders of epithelial cells lining the small intestine appear to be thickened: the thickening has striations perpendicular to the surface. This striated border of light microscopy has bcc n shown by EM to be made up of long microvilli arranged parallel to one another. In some cells the microvilli are not arranged so regularly. With the light microscope the microvilli of such cells give the appearance of a brush border. Microvilli greatly increase the surface area of the cell and are, therefore, seen most typically at sites of active absorption e.g., the intestine, and the proximal and distal convoluted tubules of the kidneys. Modified microvilli called stereocilia are seen on receptor cells in the internal ear, and on the epithelium of the epididymis. Cell inclusions Non-living, non-participating, poorly structured cell elements, very rarely seen in an intra-nuclear position; usually cytoplasmic.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Cytology Topic 4 NUCLEUS. DIVISION OF CELLS. CELL’S CYCLE Course 1

Faculty Medical The contents of the topic: The nucleus constitutes the central, more dense part of the cell. It is usually rounded or ellipsoid. Occasionally it may be elongated, indented or lobed. It is usually 4-10 um in diameter. The nucleus contains inherited information which is necessary for directing the activities of the cell as we shall see below. Nuclear constituents 1. Chromatin - mainly DNA and dispersed at interphase (except for one female X chromosome); has a fine granular appearance in routine EM, but is fibrillar; some RNA is present. 2. Nucleolus/nucleoli - dense clumped granules; nucleic acid is mainly RNA, but some DNA is there. Perinucleolar/nucleolus-associated chromatin has a special relation to the nucleolus. A range in the number of nucleoli present usually exists, e.g., in the liver cells with one nucleus, 1 to 6, with 2 the modal value. Removal of DNA by DNase allows one to see nucleoli in the very dense nuclei of lymphocytes and some other cells. 3. Nuclearmembrane – a double layered membrane that surrounded a nucleus. It content the nuclear pores. 4. Nucleoplasma – the fluid spaces between the various constituents of the nucleus.

Histological methods for the nucleus: o Nuclear structure is seen in TEM. o Radioautography for rates of cell division uses tritium-labelled precursors of nucleotides, e.g., thymidine and cytidine. Bromodeoxyuridine (BrdU) is incorporated in place of thymidine, so that cells synthesizing DNA prior to division can be revealed by a labelled antibody to the BrdU. o Chromosomes and their banding patterns are studied in cytogenetics. o Fluorescent in-situ hybridisation uses 'coloured' nucleotide probes to identify a particular chromosome and, on it, the gene of clinical interest - normal, mutated, translocated, deleted, duplicated, truncated, etc. o Silver staining reveals the nucleolar organizer regions (NORs) as intranuclear black dots, because it marks the acidic proteins binding to the genes coding for ribosomal RNA located on certain chromosomes. An increase in the number of NORs so shown (AgNORs) correlates with dysplastic (abnormal) growth, and may indicate malignant tendencies in epithelial cells. Chromatin In recent years there has been a considerable advance in our knowledge of the structure and significance of chromatin. It is made up of a substance called deoxyribonucleic acid (usually abbreviated to DNA); and of proteins. Most of the proteins in chromatin are histones. During cell division the entire chromatin within

26 the nucleus becomes very tightly coiled and takes on the appearance of a number of short, thick, rodlike structures called chromosomes. Chromosomes are made up of DNA and proteins. Proteins stabilize the structure of chromosomes.

In usual classroom slides stained with haematoxylin and eosin, the nucleus stains dark purple or blue while the cytoplasm is usually stained pink. In some cells the nuclei are relatively large and light staining. Such nuclei appear to be made up of a delicate network of fibres: the material making up the fibres of the network is called chromatin (because of its affinity for dyes). At some places (in the nucleus) the chromatin is seen in the form of irregular dark masses that are called heterochromalin (condensering). At other places the network is loose and stains lightly: the chromatin of such areas is referred to as euchromatin (decondensering). Nuclei which are large and hi which relatively large areas of euchrouiatin can be seen are referred to as open-faced nuclei. Nuclei which are made up mainly of heterochiomatin are referred to as closed-face nuclei. In addition to the masses of heterochromatin (which are irregular in outline), the nucleus shows one or more rounded, dark staining bodies called nucleoli. The nucleus also contains various small granules, fibres and vesicles (of obscure function). The spaces between the various constituents of the nucleus described above are filled by a base called the nucleoplasm. Nuclear membrane With the EM the nucleus is seen to be surrounded by a double layered nuclear membrane. The outer layer of the nuclear membrane is continuous with endoplasmic reticulum. The inner layer provides attachment to the ends of chromosomes. Deep to the inner membrane there is a layer containing proteins and a network of filaments: this layer is called the nuclear lamina. At several points the inner and outer layers of the nuclear membrane fase leaving gaps called nuclear pores. Each pore is surrounded by dense protein: the region of dense protein and the pore together - form the pore complex.

Nuclear pores represent sites at which substances can pass from the nucleus to the cytoplasm and vice versa. The nuclear pore is about 80 nm across. It is partly covered by a diaphragm which allows passage only to particles less than 9 nm in diameter. A typical nucleus has 3000 to 4000 pores.

Nucleoli We have seen that nuclei contain one or more nucleoli. They stain intensely with basic dyes like haematoxylin. In ordinary preparations they can be distinguished from heterochromatin by their rounded shape. (In contrast masses of heterochromatin are very irregular). Using histochemical procedures that distinguish between DNA and RNA it is seen

28 that the nucleoli have a high RNA content. With the EM nucleoli are seen to have a central filamentous zone (pars filamentosa) and an outer granular zone (pars granulosa) both of which are embedded in an amorphous material (pars amorphosa). Nucleoli are formed in relationship to the secondary constrictions of specific chromosomes. These regions are considered to be nucleolar organizing centres. Parts of the chromosomes located within nucleoli constitute the pars chromosoma of nucleoli.

Nucleoli are sites where ribosomal RNA is synthesized. The templates for this synthesis are located on the related chromosomes. Ribosomal RNA is at first in the form of long fibres that constitute the fibrous zone of nucleoli. It is then broken up into smaller pieces that constitute the granular zone. Finally, this RNA leaves the nucleolus, passes through a nuclear pore, and enters the cytoplasm where it takes part in protein synthesis. Multiplication of cells takes place by division of pre-existing cells. Such multiplication constitutes an essential feature of embryonic development. Cell multiplication is equally necessary after birth of the individual for growth and for replacement of dead cells. We have seen that the chromosomes within of nuclei of cells carry genetic information that call trolls the development and functioning of vat rows cells and tissues — and, therefore, of the body as a whole. When a cell divides it is essential that the whole of the genetic information within it be passed on to both the daughter cells resulting from the division. In other words the daughter cells must have chromosomes identical in number and in genetic content to those in the mother cell. This type of cell division is called mitosis. A different kind of cell division called meiosis occurs during the formation of gametes. This consists of two successive divisions called the first and second meiotic divisions. The cells resulting from these divisions (i.e., the gametes) differ from other cells in the body in that the number of chromosomes is reduced to half 29 the normal number, and the genetic information in the various gametes produced is not identical. Mitosis Many cells of the body have a limited span of functional activity at the end of which they undergo division into two daughter cells. The daughters cells hi turn have their own span of activity followed by another division. The period during which the cell is actively dividing is the phase of mitosis. The period between two successive divisions is called the interphase.

The greater part of interphase is called the G1 stage, which may last from a few hours to many years. During this period the cell carries out its 'normal' functions. Protein synthesis takes place mainly in this phase. About 12 hours before the onset of mitosis the synthesis of DNA takes place and is completed in about 7 hours: this period is called the S stage (S for synthesis). The last five hours before mitosis are utilized for synthesis of proteins required for cell division. This is called the G2 stage of interphase. Mitosis is conventionally divided into a number telophase. At this stage each chromosome consists of stages called prophase, metaphase, anaphase and telophase. The sequence of events of the mitotic cycle is best understood by starting with a cell in thelophase. With the progress of telophase the chromatin of the chromosome uncoils and elongates and the chromosome can no longer be identified as such. However, it is believed to retain its identity during the interphase (which 30 follows telophase). During the S stage of interphase the DNA content of the chromosome is duplicated so that another chromatid identical to the original one is formed: the chromosome is now made up of two chromatids. When mitosis begins (i.e., during the prophast) the chromatin of the chromosome becomes gradually more and more coiled so that the chromosome become recognizable as a thread- like structure that gradually acquires a rod-like appearance.

While the changes described above are occurring in the chromosomes a number of other events are taking place. The two centrioles separate and move to opposite poles of the cell. They produce a number of microtubules that pass from one centriole to the other and form a spindle. Tubules radiating from each centriole create a star like appearance or aster.

The spindle and the two asters collectively form the diasler (also called amphiaster or achromatic spindle). Meanwhile the nuclear membrane breaks down and the nucleoli disappear. With the formation of the spindle the chiomosomes move to a position midway between the two centrums u c., at the equator of the cell) where each chromosome becomes attached to microtubules of the spindle by its centromere. This stage is referred to as metaphase. The plane along which the chromosomes lie during metaphase is the equatorial plate. 31

In the anaphase the centromere of each chromosome splits longitudinally into two so that the chromatids now become independent chromosomes. At this stage the cell can be said to contain 46 pairs of chromosomes. One chromosome of each such pair now moves along the spindle to either pole of the cell. This is followed by telophase in which two daughter nuclei are formed by appearance of nuclear membranes around them. The chromosomes gradually elongate and become indistinct. Nucleoli reappear. The centriole is duplicated at this stage or in early interphase.

The division of the nucleus is accompanied by the division of the cytoplasm. In this process the organelles are presumably duplicated and each daughter cell comes to have a full complement of them. The rate of cell division varies from tissue to tissue being greatest fit those epithelia which lose cells because of friction (e.g., the epidermis and the lining cells of the intestine). The rate varies with demand becoming much greater during repair after injury. The rate is precisely controlled to correlate with demand. Failure of such control results in uncontrolled growth leading to formation of tumours. Various abnormalities in mitosis may be produced by exposure to various radiations, the most important being nuclear radiation. Mitosis can be arrested by chemicals. One of them — colchicin (or colcemide) — stops mitosis at metaphase and allows us to study chromosomes at this stage. Meiosis As already stated meiosis consists of two successive divisions called the first and second meiotic divisions. During the interphase preceding the first division duplication of the DNA content of the chromosomes takes place as in mitosis. First Meiotic Division The prophase of the first meiotic division is prolonged and is usually divided into a number of stages as follows. (a) Leptotene: The chromosomes become visible (as in mitosis). Although each chromosome consists of two chromatids these cannot be distinguished at this stage. At first the chromosomes are seen as threads bearing bead-like thickenings (cliromomeres) along their length. One end 32 of the thread is attached to the nuclear membrane. During leptotene the chromosomes gradually become thicker and shorter. (b) Zygotenc: We have seen that the 46 chromosomes in each cell consist of 23 pairs (the X and Y chromosomes of the male being taken as a pair). The two chromosomes of each pair come to lie parallel to each other, and are closfcly ap-posed. This pairing of chromosomes is also referred to as synopsis or conjugation The two chromosomes together constitute a bivalent. (c) Pachytene: The two chromatids of each chromosome become distinct. The bivalent now has four chromatids in it and is called a tetrad. There are two central and two peripheral chromatids, one from each chromosome. An important event now takes place. The two central chromatids (one belonging to each chromosome of the bivalent) become coiled over each other so that they cross at a number of points. This is called crossing over. At the site where the chromatids cross they become adherent: the points of adhesion are called chiasmata. (d) Diplotene: The two chromosomes of a bivalent now try to move apart. As they do so the chromatids 'break' at the points of crossing and the 'loose' pieces become attached to the opposite chromatid. This results in exchange of genetic material between these chromatids. A study of that as a result of this crossing over of genetic material each of the four chromatids of the tetrad now has a distinctive genetic content.The metaphase follows. As in mitosis the 46 chromosomes become attached to the spindle at the equator, the two chromosomes of a pair being close to each other.The anaphase differs from that in mitosis in that there is no splitting of the centromeres. One entire chromosome of each pair moves to each pole of the spindle. The resulting daughter cells, therefore, have 23 chromosomes, each made up of two chromatids.The telophase is similar to that in mitosis.The first meiotic division is followed by a short interphase. This differs from the usual interphase in that there is no duplication of DNA. Such duplication is unnecessary as the chromosomes of the cells resulting from the first meiotic division already possess two chromatids each. Second Meiotic Division The second meiotic division is similar to mitosis. However, because of the crossing over that has occurred during the first division, the daughter cells are not identical in genetic content. This is the reason for regarding it as a meiotic division. At this stage it may be repeated that the 46 chromosomes of a cell consist of 23 pairs, one chromosome of each pair being derived from the mother and one from the father. During the first meiotic division the chromosomes derived from the father and those derived from the mother are distributed between the daughter cells entirely at random. This, along with the phenomenon of crossing over, results in thorough shuffling of the genetic material so that the cells produced as a result of various meiolic divisions (i.e., ova and spermatozoa) all have a distinct genetic content. A third step in this process of genetic shuffling takes place at fertilization when there is a combination of randomly selected spermatozoa and ova. It is, therefore, not surprising that no two persons (except identical twins) are alike. Amitosis. Amitotic division at the person meets in cells of a liver and in the epithelium of urinary system. At this way of division does not occur spiralization

33 of chromosomes and the genetic material is divided any way. Distinguish two stages of amitotic division – the kariotomia and the cytoplasmotomia.

Necrosis and apoptosis. Necrosis or accidental cell death, is a pathologic process. It occurs when cells are exposed to an unfavorable physical or chemical environment (e.g., hypothermia, hypoxia, radiation, low pH, cell trauma) that causes acute cellular injury and damage to the plasma membrane. Under physiologic conditions, damage to the plasma membrane may also be initiated by viruses, substances such as complement, or proteins called perforins. Apoptosis also referred to as programmed cell death. Apoptosis is the active genetic controlled process of cellular death, which is regulated by the internal program. Apoptosis may occur during: 1) embryonic development 2) deleting of old cells 3) involution of mature tissues (follicular atresia in the ovaries) 4) the immune reactions 5) tumor growth

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Embryology Topic 5 GAMETOGENESIS Course 1

Faculty Medical The contents of the topic: Embryology is applied to the various changes which take place during the growth of an animal from the egg to the adult condition: it is, however, usually restricted to the phenomena which occur before birth. Embryology may be studied from two aspects: (1) that of ontogeny, which deals only with the development of the individual; and (2) that of phylogeny, which concerns itself with the evolutionary history of the animal kingdom. In vertebrate animals the development of a new being can only take place when a female germ cell or ovum has been fertilized by a male germ cell or spermatozoön. The ovum is a nucleated cell, and all the complicated changes by which the various tissues and organs of the body are formed from it, after it has been fertilized, are the result of two general processes, viz., segmentation and differentiation of cells. Thus, the fertilized ovum undergoes repeated segmentation into a number of cells which at first closely resemble one another, but are, sooner or later, differentiated into two groups: (1) somatic cells, the function of which is to build up the various tissues of the body; and (2) germinal cells, which become imbedded in the sexual glands - the ovaries in the female and the testes in the male and are destined for the perpetuation of the species. GAMETOGENESIS. OVOGENESIS. The ova are developed from the primitive germ cells which are imbedded in the substance of the ovaries. Each primitive germ cell gives rise, by repeated divisions, to a number of smaller cells termed oogonia, from which the ova or primary oocytes are developed. Human ova are extremely minute, measuring about 0.2 mm. in diameter, and are enclosed within the egg follicles of the ovaries; as a rule each follicle contains a single ovum, but sometimes two or more are present. By the enlargement and subsequent rupture of a follicle at the surface of the ovary, an ovum is liberated and conveyed by the uterine tube to the cavity of the uterus. Unless it is fertilized it undergoes no further development and is discharged from the uterus, but if fertilization take place it is retained within the uterus and is developed into a new being. In appearance and structure the ovum differs little from an ordinary cell, but distinctive names have been applied to its several parts; thus, the cell substance is known as the yolk or ooplasm, the nucleus as the germinal vesicle, and the nucleolus as the germinal spot. The ovum is enclosed within a thick, transparent envelope, the zona striata or zona pellucida, adhering to the outer surface of

35 which are several layers of cells, derived from those of the follicle and collectively constituting the corona radiata. Human ovum examined fresh in the liquor folliculi. The zona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granular deutoplasmic area and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot. Yolk. The yolk comprises  the cytoplasm of the ordinary animal cell with its spongioplasm and hyaloplasm; this is frequently termed the formative yolk;  the nutritive yolk or deutoplasm, which consists of numerous rounded granules of fatty and albuminoid substances imbedded in the cytoplasm. In the mammalian ovum the nutritive yolk is extremely small in amount, and is of service in nourishing the embryo in the early stages of its development only, whereas in the egg of the bird there is sufficient to supply the chick with nutriment throughout the whole period of incubation. The nutritive yolk not only varies in amount, but in its mode of distribution within the egg; thus, in some animals it is almost uniformly distributed throughout the cytoplasm; in some it is centrally placed and is surrounded by the cytoplasm; in others it is accumulated at the lower pole of the ovum, while the cytoplasm occupies the upper pole. A centrosome and centriole are present and lie in the immediate neighborhood of the nucleus. Germinal Vesicle. The germinal vesicle or nucleus is a large spherical body which at first occupies a nearly central position, but becomes eccentric as the growth of the ovum proceeds. Its structure is that of an ordinary cell-nucleus. It consists of a reticulum or karyomitome, the meshes of which are filled with karyoplasms, while connected with, or imbedded in, the reticulum are a number of chromatin masses or chromosomes, which may present the appearance of a skein or may assume the form of rods or loops. The nucleus is enclosed by a delicate nuclear membrane, and contains in its interior a well-defined nucleolus or germinal spot.

Coverings of the Ovum. The zona striata or zona pellucida is a thick membrane, which, under the higher powers of the microscope, is seen to be radially striated. It persists for some time after fertilization has occurred, and may serve for protection during the earlier stages of segmentation. It is not yet determined whether the zona striata is a product of the cytoplasm of the ovum or of the cells of the corona radiata, or both.

The corona radiata consists or two or three strata of cells; they are derived from the cells of the follicle, and adhere to the outer surface of the zona striata when the ovum is set free from the follicle; the cells are radially arranged around the zona, those of the innermost layer being columnar in shape. The cells of the corona radiata soon disappear; in some animals they secrete, or are replaced by, a layer of adhesive protein, which may assist in protecting and nourishing the ovum.

The phenomena attending the discharge of the ova from the follicles belong more to the ordinary functions of the ovary than to the general subject of embryology, and are therefore described with the anatomy of the ovaries. Maturation of the Ovum. Before an ovum can be fertilized it must undergo a process of maturation or ripening. This takes place previous to or immediately after its escape from the follicle, and consists essentially of an unequal subdivision of the ovum first into two and then into four cells. Three of the four cells are small, incapable of further development, and are termed polar bodies or polocytes, while the fourth is large, and constitutes the mature ovum.The process of maturation has not been observed in the human ovum, but has been carefully studied. The number of chromosomes found in the nucleus is constant for all the cells in an animal of any given species, and that in man the number is probably twenty-four. This applies not only to the somatic cells but to the primitive ova and their descendants. For the purpose of illustrating the process of maturation a species may be taken in which the number of nuclear chromosomes is four. If an ovum from such be observed at the beginning of the maturation process it will be seen that the number of its chromosomes is apparently reduced to two. In reality, however, the number is doubled, since each chromosome consists of four granules grouped to form a tetrad. During the metaphase each tetrad divides into two dyads, which are equally distributed between the nuclei of the two cells formed by the first division of the ovum. One of the cells is almost as large as the original ovum, and is named the secondary oocyte; the other is small, and is termed the first polar body. The secondary oöcyte now undergoes subdivision, during which each dyad divides and contributes a single chromosome to the nucleus of each of the two resulting cells. This second division is also unequal, producing a large cell which constitutes the mature ovum, and a small cell, the second polar body. The first polar body frequently divides while the second is being formed, and as a final

38 result four cells are produced, viz., the mature ovum and three polar bodies, each of which contains two chromosomes, i.e., one-half the number present in the nuclei of the somatic cells of members of the same species. The nucleus of the mature ovum is termed the female pronucleus. SPERMATOGENESIS. The spermatozoa or male germ cells are developed in the testes and are present in enormous numbers in the seminal fluid. Each consists of a small but greatly modified cell. The human spermatozoön possesses a head, a neck, a connecting piece or body, and a tail. The head is oval or elliptical, but flattened, so that when viewed in profile it is pear-shaped. Its anterior two-thirds are covered by a layer of modified protoplasm, which is named the head-cap. The posterior part of the head exhibits an affinity for certain reagents, and presents a transversely striated appearance, being crossed by three or four dark bands. In some animals a central rodlike filament extends forward for about two-thirds of the length of the head, while in others a rounded body is seen near its center. The head contains a mass of chromatin, and is generally regarded as the nucleus of the cell surrounded by a thin envelope.

The neck is less constricted in the human spermatozoön than in those of some of the lower animals. The anterior centriole, represented by two or three rounded particles, is situated at the junction of the head and neck, and behind it is a band of homogeneous substance. The connecting piece or body is rod-like, and is limited behind by a terminal disk. The posterior centriole is placed at the junction of the body and neck and, like the anterior, consists of two or three rounded particles. From this centriole an axial filament, surrounded by a sheath, runs backward through the body and tail. In the body the sheath of the axial filament is encircled by a spiral 39 thread, around which is an envelope containing mitochondria granules, and termed the mitochondria sheath. The tail is of great length, and consists of the axial thread or filament, surrounded by its sheath, which may contain a spiral thread or may present a striated appearance. The terminal portion or end-piece of the tail consists of the axial filament only. By virtue of their tails, which act as propellers, the spermatozoa are capable of free movement, and if placed in favorable surroundings, e. g., in the female passages, will retain their vitality and power of fertilizing for several days. In certain animals, e. g., bats, it has been proved that spermatozoa retained in the female passages for several months are capable of fertilizing. The spermatozoa are developed from the primitive germ cells which have become imbedded in the testes, and the stages of their development are very similar to those of the maturation of the ovum. The primary germ cells undergo division and produce a number of cells termed spermatogonia, and from these the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two spermatids or young spermatozoa; from this it will be seen that a primary spermatocyte gives rise to four spermatozoa. On comparing this process with that of the maturation of the ovum it will be observed that the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the primary oöcyte to two cells, the secondary oöcyte and the first polar body. Again, the two secondary spermatocytes by their subdivision give origin to four spermatozoa, and the secondary oöcyte and first polar body to four cells, the mature ovum and three polar bodies. In the development of the spermatozoa, as in the maturation of the ovum, there is a reduction of the nuclear chromosomes to one-half of those present in the primary spermatocyte. But here the similarity ends, for it must be noted that the four spermatozoa are of equal size, and each is capable of fertilizing a mature ovum, whereas the three polar bodies are not only very much smaller than the mature ovum but are incapable of further development, and may be regarded as abortive ova.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Embryology Topic 6 FERTILIZATION. SEGMENTATION. IMPLANTATION Course 1

Faculty Medical The contents of the topic: Fertilization of the Ovum Fertilization consists in the union of the spermatozoön with the mature ovum. Nothing is known regarding the fertilization of the human ovum, but the various stages of the process have been studied in other mammals, and from the knowledge so obtained it is believed that fertilization of the human ovum takes place in the lateral or ampullary part of the uterine tube, and the ovum is then conveyed along the tube to the cavity of the uterus—a journey probably occupying seven or eight days and during which the ovum loses its corona radiata and zona striata and undergoes segmentation. Sometimes the fertilized ovum is arrested in the uterine tube, and there undergoes development, giving rise to a tubal pregnancy; or it may fall into the abdominal cavity and produce an abdominal pregnancy.

Occasionally the ovum is not expelled from the follicle when the latter ruptures, but is fertilized within the follicle and produces what is known as an ovarian pregnancy. Under normal conditions only one spermatozoön enters the yolk and takes part in the process of fertilization. At the point where the spermatozoön is about to pierce, the yolk is drawn out into a conical elevation, termed the cone of attraction.

As soon as the spermatozoön has entered the yolk, the peripheral portion of the latter is transformed into a membrane, the vitelline membrane which prevents the passage of additional spermatozoa.

Occasionally a second spermatozoön may enter the yolk, thus giving rise to a condition of polyspermy: when this occurs the ovum usually develops in an abnormal manner and gives rise to a monstrosity. Having pierced the yolk, the spermatozoön loses its tail, while its head and connecting piece assume the form of a nucleus containing a cluster of chromosomes. This constitutes the male pronucleus, and associated with it there are a centriole and centrosome. The male pronucleus passes more deeply into the yolk, and coincidently with this the granules of the cytoplasm surrounding it become radially arranged. The male and 42 female pronuclei migrate toward each other, and, meeting near the center of the yolk, fuse to form a new nucleus, the segmentation nucleus, which therefore contains both male and female nuclear substance; the former transmits the individualities of the male ancestors, the latter those of the female ancestors, to the future embryo. By the union of the male and female pronuclei the number of chromosomes is restored to that which is present in the nuclei of the somatic cells. Segmentation of the Fertilized Ovum The early segmentation of the human ovum has not yet been observed, but judging from what is known to occur in other mammals it may be regarded as certain that the process starts immediately after the ovum has been fertilized, i. e., while the ovum is in the uterine tube. The segmentation nucleus exhibits the usual mitotic changes, and these are succeeded by a division of the ovum into two cells of nearly equal size. The process is repeated again and again, so that the two cells are succeeded by four, eight, sixteen, thirty-two, and so on, with the result that a mass of cells is found within the zona striata, and to this mass the term morula is applied. The segmentation of the mammalian ovum may not take place in the regular sequence of two, four, eight, etc., since one of the two first formed cells may subdivide more rapidly than the other, giving rise to a three-or a five-cell stage. The cells of the morula are at first closely aggregated, but soon they become arranged into an outer or peripheral layer, the trophoblast, which does not contribute to the formation of the embryo proper, and an inner cell-mass, from which the embryo is developed. Fluid collects between the trophoblast and the greater part of the inner cell-mass, and thus the morula is converted into a vesicle, the blastodermic vesicle.

The inner cell-mass remains in contact, however, with the trophoblast at one pole of the ovum; this is named the embryonic pole, since it indicates the situation where the future embryo will be developed. The cells of the trophoblast become differentiated into two strata: an outer, termed the syncytium or syncytiotrophoblast, so named because it consists of a layer of protoplasm studded with nuclei, but showing no evidence of subdivision into cells; and an inner layer, the cytotrophoblast or layer of Langhans, in which the cell outlines are defined. As already stated, the cells of the trophoblast do not contribute to the formation of the embryo proper; they form the ectoderm of the chorion and play an important part in the development of the placenta. On the deep surface of the inner cell-mass a layer of flattened cells, the entoderm, is differentiated and quickly assumes the form of a small sac, the yolk-sac. Spaces appear between the remaining cells of the mass and by the enlargement and coalescence of these spaces a cavity, termed the amniotic cavity is gradually developed. The floor of this cavity is formed by the embryonic disk composed of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell-mass and lying in apposition with the entoderm.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Embryology Topic 7 GASTRULATION Course 1

Faculty Medical The contents of the topic: The Primitive Streak. Formation of the Mesoderm. The embryonic disk becomes oval and then pear-shaped, the wider end being directed forward. Near the narrow, posterior end an opaque streak, the primitive streak, makes its appearance and extends along the middle of the disk for about one-half of its length; at the anterior end of the streak there is a knob-like thickening termed Hensen’s knot. A shallow groove, the primitive groove, appears on the surface of the streak, and the anterior end of this groove communicates by means of an aperture, the blastophore, with the yolk-sac. The primitive streak is produced by a thickening of the axial part of the ectoderm, the cells of which multiply, grow downward, and blend with those of the subjacent entoderm. From the sides of the primitive streak a third layer of cells, the mesoderm, extends lateralward between the ectoderm and entoderm; the caudal end of the primitive streak forms the cloacal membrane. The extension of the mesoderm takes place throughout the whole of the embryonic and extra-embryonic areas of the ovum, except in certain regions. One of these is seen immediately in front of the neural tube. Here the mesoderm extends forward in the form of two crescentic masses, which meet in the middle line so as to enclose behind them an area which is devoid of mesoderm.

Over this area the ectoderm and entoderm come into direct contact with each other and constitute a thin membrane, the buccopharyngeal membrane, which forms a septum between the primitive mouth and pharynx. In front of the buccopharyngeal area, where the lateral crescents of mesoderm fuse in the middle line, the pericardium is afterward developed, and this region is therefore designated the pericardial area. A second region where the mesoderm is absent, at least for a time, is that immediately in front of the pericardial area. This is termed the proamniotic area, and is the region where the proamnion is developed; in man, however, a proamnion is apparently never formed. A third region is at the hind end of the embryo where the ectoderm and entoderm come into apposition and form the cloacal membrane. The blastoderm now consists of three layers, named from without inward: ectoderm, mesoderm, and entoderm; each has distinctive characteristics and gives rise to certain tissues of the body. Ectoderm. The ectoderm consists of columnar cells, which are, however, somewhat flattened or cubical toward the margin of the embryonic disk. It forms the whole of the nervous system, the epidermis of the skin, the lining cells of the sebaceous, sudoriferous, and mammary glands, the hairs and nails, the epithelium of the nose and adjacent air sinuses, and that of the cheeks and roof of the mouth. From it also are derived the enamel of the teeth, and the anterior lobe of the hypophysis cerebri, the epithelium of the cornea, conjunctiva, and lacrimal glands, and the neuroepithelium of the sense organs.

Entoderm. The entoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the digestive tube excepting part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm), the lining cells of all the glands which open into the digestive tube, including those of the liver and pancreas, the epithelium of the auditory tube and tympanic cavity, of the trachea, bronchi, and air cells of the lungs, of the urinary bladder and part of the urethra, and that which lines the follicles of the thyroid gland and thymus. Mesoderm. The mesoderm consists of loosely arranged branched cells surrounded by a considerable amount of intercellular fluid. From it the remaining tissues of the body are developed. The endothelial lining of the heart and blood-vessels and the blood corpuscles are, however, regarded by some as being of entodermal origin. As the mesoderm develops between the ectoderm and entoderm it is separated into lateral halves by the neural tube and notochord, presently to be described. A longitudinal groove appears on the dorsal surface of either half and divides it into a medial column, the paraxial mesoderm, lying on the side of the neural tube, and a lateral portion, the lateral mesoderm.

The mesoderm in the floor of the groove connects the paraxial with the lateral mesoderm and is known as the intermediate cell-mass; in it the genito- urinary organs are developed. The lateral mesoderm splits into two layers, an outer or somatic, which becomes applied to the inner surface of the ectoderm, and with it forms the somatopleure; and an inner or splanchnic, which adheres to the entoderm, and with it forms the splanchnopleure. The space between the two layers of the lateral mesoderm is termed the celom.In the mammalian ova the nutritive yolk or deutoplasm is small in amount and uniformly distributed throughout the cytoplasm; such ova undergo complete division during the process of segmentation, and are therefore termed holoblastic. In the ova of birds, reptiles, and fishes where the nutritive yolk forms by far the larger portion of the egg, the cleavage is limited to the formative yolk, and is therefore only partial; such ova are termed meroblastic. Again, it has been observed, in some of the lower animals, which the pronuclei do not fuse but merely lie in apposition. At the 47 commencement of the segmentation process the chromosomes of the two pronuclei group themselves around the equator of the nuclear spindle and then divide; an equal number of male and female chromosomes travel to the opposite poles of the spindle, and thus the male and female pronuclei contribute equal shares of chromatin to the nuclei of the two cells which result from the subdivision of the fertilized ovum. The Neural Groove and Tube In front of the primitive streak two longitudinal ridges, caused by a folding up of the ectoderm, make their appearance, one on either side of the middle line. These are named the neural folds; they commence some little distance behind the anterior end of the embryonic disk, where they are continuous with each other, and from there gradually extend backward, one on either side of the anterior end of the primitive streak. Between these folds is a shallow median groove, the neural groove. The groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into a closed tube, the neural tube or canal, the ectodermal wall of which forms the rudiment of the nervous system. After the coalescence of the neural folds over the anterior end of the primitive streak, the blastopore no longer opens on the surface but into the closed canal of the neural tube, and thus a transitory communication, the neurenteric canal, is established between the neural tube and the primitive digestive tube. The coalescence of the neural folds occurs first in the region of the hind-brain, and from there extends forward and backward; toward the end of the third week the front opening (anterior neuropore) of the tube finally closes at the anterior end of the future brain, and forms a recess which is in contact, for a time, with the overlying ectoderm; the hinder part of the neural groove presents for a time a rhomboidal shape, and to this expanded portion the term sinus rhomboidalis.

Before the neural groove is closed a ridge of ectodermal cells appears along the prominent margin of each neural fold; this is termed the neural crest or ganglion ridge, and from it the spinal and cranial nerve ganglia and the ganglia of 48 the sympathetic nervous system are developed. By the upward growth of the mesoderm the neural tube is ultimately separated from the overlying ectoderm. The cephalic end of the neural groove exhibits several dilatations, which, when the tube is closed, assume the form of three vesicles; these constitute the three primary cerebral vesicles, and correspond respectively to the future fore- brain (prosencephalon), mid-brain (mesencephalon), and hind-brain (rhombencephalon). The walls of the vesicles are developed into the nervous tissue and neuroglia of the brain, and their cavities are modified to form its ventricles. The remainder of the tube forms the medulla spinalis or spinal cord; from its ectodermal wall the nervous and neuroglial elements of the medulla spinalis are developed while the cavity persists as the central canal. The notochord consists of a rod of cells situated on the ventral aspect of the neural tube; it constitutes the foundation of the axial skeleton, since around it the segments of the vertebral column are formed. Its appearance synchronizes with that of the neural tube. On the ventral aspect of the neural groove an axial thickening of the entoderm takes place; this thickening assumes the appearance of a furrow—the chordal furrow—the margins of which come into contact, and so convert it into a solid rod of cells—the notochord—which is then separated from the entoderm. It extends throughout the entire length of the future vertebral column, and reaches as far as the anterior end of the mid-brain, where it ends in a hook-like extremity in the region of the future dorsum sellæ of the sphenoid bone. It lies at first between the neural tube and the entoderm of the yolk-sac, but soon becomes separated from them by the mesoderm, which grows medial-ward and surrounds it. From the mesoderm surrounding the neural tube and notochord, the skull and vertebral column, and the membranes of the brain and medulla spinalis are developed. The Primitive Segments Toward the end of the second week transverse segmentation of the paraxial mesoderm begins, and it is converted into a series of well-defined, more or less cubical masses, the primitive segments, which occupy the entire length of the trunk on either side of the middle line from the occipital region of the head. Each segment contains a central cavity—myocœl—which, however, is soon filled with angular and spindle-shaped cells.

The primitive segments lie immediately under the ectoderm on the lateral aspect of the neural tube and notochord, and are connected to the lateral mesoderm by the intermediate cell-mass. Those of the trunk may be arranged in the following groups, viz.: cervical 8, thoracic 12, lumbar 5, sacral 5, and coccygeal from 5 to 8. Those of the occipital region of the head are usually described as being four in number. In mammals primitive segments of the head can be recognized only in the occipital region, but a study of the lower vertebrates leads to the belief that they are present also in the anterior part of the head, and that altogether nine segments are represented in the cephalic region.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Embryology Topic 8 PROVISIONAL ORGANS OF THE EMBRYO Course 1

Faculty Medical The contents of the topic: Separation of the Embryo The embryo increases rapidly in size, but the circumference of the embryonic disk, or line of meeting of the embryonic and amniotic parts of the ectoderm, is of relatively slow growth and gradually comes to form a constriction between the embryo and the greater part of the yolk-sac. By means of this constriction, which corresponds to the future umbilicus, a small part of the yolk- sac is enclosed within the embryo and constitutes the primitive digestive tube. The embryo increases more rapidly in length than in width, and its cephalic and caudal ends soon extend beyond the corresponding parts of the circumference of the embryonic disk and are bent in a ventral direction to form the cephalic and caudal folds respectively. The cephalic fold is first formed, and as the proamniotic area lying immediately in front of the pericardial area forms the anterior limit of the circumference of the embryonic disk, the forward growth of the head necessarily carries with it the posterior end of the pericardial area, so that this area and the buccopharyngeal membrane are folded back under the head of the embryo which now encloses a diverticulum of the yolk-sac named the fore-gut. The caudal end of the embryo is at first connected to the chorion by a band of mesoderm called the body-stalk, but with the formation of the caudal fold the body-stalk assumes a ventral position; a diverticulum of the yolk-sac extends into the tail fold and is termed the hind-gut. Between the fore-gut and the hind-gut there exists for a time a wide opening into the yolk-sac, but the latter is gradually reduced to a small pear-shaped sac (sometimes termed the umbilical vesicle), and the channel of communication is at the same time narrowed and elongated to form a tube called the vitelline duct. The yolk-sac is situated on the ventral aspect of the embryo; it is lined by entoderm, outside of which is a layer of mesoderm. It is filled with fluid, the vitelline fluid, which possibly may be utilized for the nourishment of the embryo during the earlier stages of its existence. Blood is conveyed to the wall of the sac by the primitive aortæ, and after circulating through a wide-meshed capillary plexus, is returned by the vitelline veins to the tubular heart of the embryo. This constitutes the vitelline circulation, and by means of it nutritive material is absorbed from the yolk-sac and conveyed to the embryo. At the end of the fourth week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct. The vesicle can be seen in the after-birth as a small, somewhat oval- shaped body whose diameter varies from 1 mm. to 5 mm; it is situated between the 51 amnion and the chorion and may lie on or at a varying distance from the placenta. As a rule the duct undergoes complete obliteration during the seventh week, but in about three per cent. of cases its proximal part persists as a diverticulum from the small intestine, Meckel’s diverticulum, which is situated about three or four feet above the ileocolic junction, and may be attached by a fibrous cord to the abdominal wall at the umbilicus. Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct. Development of the Fetal Membranes and Placenta The Allantois The allantois arises as a tubular diverticulum of the posterior part of the yolk-sac; when the hind-gut is developed the allantois is carried backward with it and then opens into the cloaca or terminal part of the hind-gut: it grows out into the body-stalk, a mass of mesoderm which lies below and around the tail end of the embryo. The diverticulum is lined by entoderm and covered by mesoderm, and in the latter are carried the allantoic or umbilical vessels. In reptiles, birds, and many mammals the allantois becomes expanded into a vesicle which projects into the extra-embryonic celom. If its further development be traced in the bird, it is seen to project to the right side of the embryo, and, gradually expanding, it spreads over its dorsal surface as a flattened sac between the amnion and the serosa, and extending in all directions, ultimately surrounds the yolk. Its outer wall becomes applied to and fuses with the serosa, which lies immediately inside the shell membrane. Blood is carried to the allantoic sac by the two allantoic or umbilical arteries, which are continuous with the primitive aortæ, and after circulating through the allantoic capillaries, is returned to the primitive heart by the two umbilical veins. In this way the allantoic circulation, which is of the utmost importance in connection with the respiration and nutrition of the chick, is established. Oxygen is taken from, and carbonic acid is given up to the atmosphere through the egg-shell, while nutritive materials are at the same time absorbed by the blood from the yolk. In man and other primates the nature of the allantois is entirely different from that just described. Here it exists merely as a narrow, tubular diverticulum of the hind-gut, and never assumes the form of a vesicle outside the embryo. With the formation of the amnion the embryo is, in most animals, entirely separated from the chorion, and is only again united to it when the allantoic mesoderm spreads over and becomes applied to its inner surface. The human embryo, on the other hand, as was pointed out by His, is never wholly separated from the chorion, its tail end being from the first connected with the chorion by means of a thick band of mesoderm, named the body-stalk (Bauchstiel); into this stalk the tube of the allantois extends. The Amnion. The amnion is a membranous sac which surrounds and protects the embryo. In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac, and, as indicated on page 46, appears in the inner

52 cell-mass as a cavity. This cavity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk—the continuity between the roof and floor being established at the margin of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion. When first formed the amnion is in contact with the body of the embryo, but about the fourth or fifth week fluid (liquor amnii) begins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the celom is obliterated. The liquor amnii increases in quantity up to the sixth or seventh month of pregnancy, after which it diminishes somewhat; at the end of pregnancy it amounts to about 1 liter. It allows of the free movements of the fetus during the later stages of pregnancy, and also protects it by diminishing the risk of injury from without. It contains less than 2 per cent. of solids, consisting of urea and other extractives, inorganic salts, a small amount of protein, and frequently a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved by the fact that epidermal debris and hairs have been found among the contents of the fetal alimentary canal. In reptiles, birds, and many mammals the amnion is developed in the following manner: At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes place. This, the amniotic fold first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo, and gradually rising more and more, its different parts meet and fuse over the dorsal aspect of the embryo, and enclose a cavity, the amniotic cavity. After the fusion of the edges of the amniotic fold, the two layers of the fold become completely separated, the inner forming the amnion, the outer the false amnion or serosa. The space between the amnion and the serosa constitutes the extra-embryonic celom, and for a time communicates with the embryonic celom.

The Umbilical Cord and Body-stalk. The umbilical cord attaches the fetus to the placenta; its length at full time, as a rule, is about equal to the length of the fetus, i.e., about 50 cm., but it may be greatly diminished or increased. The rudiment of the umbilical cord is represented by the tissue which connects the rapidly growing embryo with the extra-embryonic area of the ovum. Included in this tissue are the body-stalk and the vitelline duct— the former containing the allantoic diverticulum and the umbilical vessels, the latter forming the communication between the digestive tube and the yolk-sac. The body-stalk is the posterior segment of the embryonic area, and is attached to the chorion. It consists of a plate of mesoderm covered by thickened ectoderm on which a trace of the neural groove can be seen, indicating its continuity with the embryo. Running through its mesoderm are the two umbilical arteries and the two umbilical veins, together with the canal of the allantois—the last being lined by entoderm. Its dorsal surface is covered by the amnion, while its ventral surface is bounded by the extra-embryonic celom, and is in contact with the vitelline duct and yolk-sac. With the rapid elongation of the embryo and the formation of the tail fold, the body stalk comes to lie on the ventral surface of the embryo, where its mesoderm blends with that of the yolk-sac and the vitelline duct. The lateral leaves of somatopleure then grow round on each side, and, meeting on the ventral aspect of the allantois, enclose the vitelline duct and vessels, together with a part of the extra-embryonic celom; the latter is ultimately obliterated. The cord is covered by a layer of ectoderm which is continuous with that of the amnion, and its various constitutents are enveloped by embryonic gelatinous tissue, jelly of Wharton. The vitelline vessels and duct, together with the right umbilical vein, undergo atrophy and disappear; and thus the cord, at birth, contains a pair of umbilical arteries and one (the left) umbilical vein. Implantation or Imbedding of the Ovum. Fertilization of the ovum occurs in the lateral or ampullary end of the uterine tube and is immediately followed by segmentation. On reaching the cavity of the uterus the segmented ovum adheres like a parasite to the uterine mucous membrane, destroys the epithelium over the area of contact, and excavates for itself a cavity in the mucous membrane in which it becomes imbedded. Soon, all 54 trace of the opening is lost and the ovum is then completely surrounded by the uterine mucous membrane. The structure actively concerned in the process of excavation is the trophoblast of the ovum, which possesses the power of dissolving and absorbing the uterine tissues. The trophoblast proliferates rapidly and forms a network of branching processes which cover the entire ovum and invade and destroy the maternal tissues and open into the maternal bloodvessels, with the result that the spaces in the trophoblastic network are filled with maternal blood; these spaces communicate freely with one another and become greatly distended and form the intervillous space. The Decidua. Before the fertilized ovum reaches the uterus, the mucous membrane of the body of the uterus undergoes important changes and is then known as the decidua. The thickness and vascularity of the mucous membrane are greatly increased; its glands are elongated and open on its free surface by funnel-shaped orifices, while their deeper portions are tortuous and dilated into irregular spaces. The interglandular tissue is also increased in quantity, and is crowded with large round, oval, or polygonal cells, termed decidual cells. These changes are well advanced by the second month of pregnancy, when the mucous membrane consists of the following strata: (1) stratum compactum, next the free surface; in this the uterine glands are only slightly expanded, and are lined by columnar cells; (2) stratum spongiosum, in which the gland tubes are greatly dilated and very tortuous, and are ultimately separated from one another by only a small amount of interglandular tissue, while their lining cells are flattened or cubical; (3) a thin unaltered or boundary layer, next the uterine muscular fibers, containing the deepest parts of the uterine glands, which are not dilated, and are lined with columnar epithelium; it is from this epithelium that the epithelial lining of the uterus is regenerated after pregnancy. Distinctive names are applied to different portions of the decidua. The part which covers in the ovum is named the decidua capsularis; the portion which intervenes between the ovum and the uterine wall is named the decidua basalis or decidua placentalis; it is here that the placenta is subsequently developed. The part of the decidua which lines the remainder of the body of the uterus is known as the decidua vera or decidua parietalis. The Chorion The chorion consists of two layers: an outer formed by the primitive ectoderm or trophoblast, and an inner by the somatic mesoderm; with this latter the amnion is in contact. The trophoblast is made up of an internal layer of cubical or prismatic cells, the cytotrophoblast or layer of Langhans, and an external layer of richly nucleated protoplasm devoid of cell boundaries, the syncytiotrophoblast. It undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo.

The chorionic villi are at first small and non-vascular, and consist of trophoblast only, but they increase in size and ramify, while the mesoderm, carrying branches of the umbilical vessels, grows into them, and in this way they are vascularized. Blood is carried to the villi by the branches of the umbilical arteries, and after circulating through the capillaries of the villi, is returned to the embryo by the umbilical veins. Until about the end of the second month of pregnancy the villi cover the entire chorion, and are almost uniform in size, but after this they develop unequally. The greater part of the chorion is in contact with the decidua capsularis, and over this portion the villi, with their contained vessels, undergo atrophy, so that by the fourth month scarcely a trace of them is left, and hence this part of the chorion becomes smooth, and is named the chorion læve; as it takes no share in the formation of the placenta, it is also named the non-placental part of the chorion. On the other hand, the villi on that part of the chorion which is in contact with the decidua placentalis increase greatly in size and complexity, and hence this part is named the chorion frondosum. The Placenta. The placenta connects the fetus to the uterine wall, and is the organ by means of which the nutritive, respiratory, and excretory functions of the fetus are carried on. It is composed of fetal and maternal portions.

Fetal Portion. The fetal portion of the placenta consists of the villi of the chorion frondosum; these branch repeatedly, and increase enormously in size. These greatly ramified villi are suspended in the intervillous space, and are bathed in maternal blood, which is conveyed to the space by the uterine arteries and carried away by the uterine veins. A branch of an umbilical artery enters each villus and ends in a capillary plexus from which the blood is drained by a tributary of the umbilical vein. The vessels of the villus are surrounded by a thin layer of mesoderm consisting of gelatinous connective tissue, which is covered by two strata of ectodermal cells derived from the trophoblast: the deeper stratum, next the mesodermic tissue, represents the cytotrophoblast or layer of Langhans; the superficial, in contact with the maternal blood, the syncytiotrophoblast. After the fifth month the two strata of cells are replaced by a single layer of somewhat flattened cells. Maternal Portion. The maternal portion of the placenta is formed by the decidua placentalis containing the intervillous space. As already explained, this space is produced by the enlargement and intercommunication of the spaces in the trophoblastic network. The changes involve the disappearance of the greater portion of the stratum compactum, but the deeper part of this layer persists and is condensed to form what is known as the basal plate. Between this plate and the uterine muscular fibres are the stratum spongiosum and the boundary layer; through these and the basal plate the uterine arteries and veins pass to and from the intervillous space. The endothelial lining of the uterine vessels ceases at the point where they terminate in the intervillous space which is lined by the syncytiotrophoblast. Portions of the stratum compactum persist and are condensed to form a series of septa, which extend from the basal plate through the thickness of the placenta and 57 subdivide it into the lobules or cotyledons seen on the uterine surface of the detached placenta. The fetal and maternal blood currents traverse the placenta, the former passing through the bloodvessels of the placental villi and the latter through the intervillous space. The two currents do not intermingle, being separated from each other by the delicate walls of the villi. Nevertheless, the fetal blood is able to absorb, through the walls of the villi, oxygen and nutritive materials from the maternal blood, and give up to the latter its waste products. The blood, so purified, is carried back to the fetus by the umbilical vein. It will thus be seen that the placenta not only establishes a mechanical connection between the mother and the fetus, but subserves for the latter the purposes of nutrition, respiration, and excretion. In favor of the view that the placenta possesses certain selective powers may be mentioned the fact that glucose is more plentiful in the maternal than in the fetal blood. It is interesting to note also that the proportion of iron, and of lime and potash, in the fetus is increased during the last months of pregnancy. Further, there is evidence that the maternal leucocytes may migrate into the fetal blood, since leucocytes are much more numerous in the blood of the umbilical vein than in that of the umbilical arteries. Separation of the Placenta. After the child is born, the placenta and membranes are expelled from the uterus as the after-birth. The separation of the placenta from the uterine wall takes place through the stratum spongiosum, and necessarily causes rupture of the uterine vessels. The orifices of the torn vessels are, however, closed by the firm contraction of the uterine muscular fibers, and thus postpartum hemorrhage is controlled. The epithelial lining of the uterus is regenerated by the proliferation and extension of the epithelium which lines the persistent portions of the uterine glands in the unaltered layer of the decidua. The expelled placenta appears as a discoid mass which weighs about 450 gm. and has a diameter of from 15 to 20 cm. Its average thickness is about 3 cm., but this diminishes rapidly toward the circumference of the disk, which is continuous with the membranes. Its uterine surface is divided by a series of fissures into lobules or cotyledons, the fissures containing the remains of the septa which extended between the maternal and fetal portions. Most of these septa end in irregular or pointed processes; others, especially those near the edge of the placenta, pass through its thickness and are attached to the chorion. In the early months these septa convey branches of the uterine arteries which open into the intervillous space on the surfaces of the septa. The fetal surface of the placenta is smooth, being closely invested by the amnion. Seen through the latter, the chorion presents a mottled appearance, consisting of gray, purple, or yellowish areas. The umbilical cord is usually attached near the center of the placenta, but may be inserted anywhere between the center and the margin; in some cases it is inserted into the membranes, i. e., the velamentous insertion.

On section, the placenta presents a soft, spongy appearance, caused by the greatly branched villi; surrounding them is a varying amount of maternal blood giving the dark red color to the placenta. Many of the larger villi extend from the chorionic to the decidual surface, while others are attached to the septa which separate the cotyledons; but the great majority of the villi hang free in the intervillous space. In the human embryo described by the mesoderm outside the embryonic disk is split into two layers enclosing an extra-embryonic cœlom; there is no trace of an intra-embryonic cœlom. At a later stage four cavities are formed within the embryo, viz., one on either side within the mesoderm of the pericardial area, and one in either lateral mass of the general mesoderm. All these are at first independent of each other and of the extra-embryonic celom, but later they become continuous. The two cavities in the general mesoderm unite on the ventral aspect of the gut and form the pleuro-peritoneal cavity, which becomes continuous with the remains of the extra-embryonic celom around the umbilicus; the two cavities in the pericardial area rapidly join to form a single pericardial cavity, and this from two lateral diverticula extend caudalward to open into the pleuro-peritoneal cavity. Between the two latter diverticula is a mass of mesoderm containing the ducts of Cuvier, and this is continuous ventrally with the mesoderm in which the umbilical veins are passing to the sinus venosus. A septum of mesoderm thus extends across the body of the embryo. It is attached in front to the body-wall between the pericardium and umbilicus; behind to the body-wall at the level of the second cervical segment; laterally it is deficient where the pericardial and pleuro- peritoneal cavities communicate, while it is perforated in the middle line by the foregut. This partition is termed the septum transversum, and is at first a bulky plate of tissue. As development proceeds the dorsal end of the septum is carried gradually caudalward, and when it reaches the fifth cervical segment muscular tissue with the phrenic nerve grows into it. It continues to recede, however, until it reaches the position of the adult diaphragm on the bodies of the upper lumbar vertebræ. The liver buds grow into the septum transversum and undergo development there. The lung buds meantime have grown out from the fore-gut, and project laterally into the forepart of the pleuro-peritoneal cavity; the developing stomach and liver are imbedded in the septum transversum; caudal to this the intestines project into the back part of the pleuro-peritoneal cavity. Owing to the descent of the dorsal end of the septum transversum the lung buds come to lie above the septum and thus pleural and peritoneal portions of the pleuro-peritoneal cavity (still, however, in free communication with one another) may be recognized; the pericardial cavity opens into the pleural part.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №1 Embryology Topic 9 CONTROL TESTS Course 1

Faculty Medical The contents of the topic: A. Questions to be answered: 1. What is the subject of Histology? 2. What are the methods of histological investigations? 3. What are the steps of the preparation of the material? 4. What is the construction of light microscope and rule of use it? 5. What differences between light and electron microscopes? 6. What methods of painting are most accessible to studying a structure of biological objects? 7. What is the cell? 8. What about you know what basic functions of cells? 9. Name the basic components of a cell? 10. What are the basic functions of plasmalemma? 11. What are distinguishing specific membranes proteins? 12. How is the elementary biological membrane constructed? 13. What are the contacts between adjoining cells? 14. Describe a structure of zonula occludense? 15. Describe a structure of desmosomes (maculae adherens) and zonula adherens? 16. What is nexus?What is the junctional complex? 17. What is the cytoplasm? 18. Give the classification of the organelles? 19. Describe a structure of the mitochondria? 20. Give the characteristics of the endoplasmic reticulum? 21. What is the Golgi complex? 22. Describe the structure of lysosomes? 23. Give the characteristics of the ribosomes? 24. Describe the structure of microfilaments and microtubules? 25. Give the characteristics of centrioles? 26. Describe the structure of the cilia? 27. Give the characteristics of flagella? 28. Describe the structure of the microvilli? 29. Give the characteristics of cell inclusions? 30. What nuclear constituents do you know? 31. Give the characteristics of the chromatin? 32. Describe a structure of the nuclear membrane? 33. Describe a structure of the nuclear pores? 60

34. Nature and Significance of Chromatin? 35. Give the characteristics of the nucleoli? 36. What is the cell’s cycle? 37. Characterize the mitosis? 38. What is the meiosis? 39. Give the characteristics of the first meiotic division? 40. Give the characteristics of the second meiotic division? 41. What is the amitosis? 42. Give the characteristics of the stem cells? 43. Endomitosis. Poliploidiya.Vnutrikletochnaya regeneration. 44. Hypertrophy of cells.Atrophy of cells. 45. Adaptation of cages, its value for the maintainance of life of cells in the changed terms of existence. 46. Apoptosis and his biological and medical value. 47. Senescence and death of cell. Necrosis. 48. Ovary. A constitution, function of different parenchymatous units in genesial period. 49. Endocrine function of the ovary, its hormonal regulation. Changes of the ovaries parenchima in follicular phase of ovarian cycle. 50. Endocrine function of an ovary. Changes of structural units in lutear phase of an ovarian cycle. 51. Uterus. Constitution, function. Cyclic changes of the uterus wall and their hormonal regulation. Age changes. 52. Endocrine regulation of the female reproductive system functions. Оvarian cycle, characteristic of phases. 53. Mammary glands. Features of structure. A hormonal regulation of mammary glans. Target cells. 54. Embryogenesis. Its stages. Value for a fetus. 55. Progenesis, as the first stage of an ontogenesis. Probable deviations in a progenesis, which one conduct to a pathology of development. 56. Gametes, their difference from somatic cells. A role of a nucleus and cytoplasm in transmission and implementation of the heritable information. 57. Spermatogenesis. Its periods. Their mоrfo-functional characteristic. 58. Functional value of formation period in the spermatogenesis. The morphological characteristic of a mature spermatozoon. 59. Ovogenesis, its periods. Their моrfо-functional characteristic. 60. Comparative characteristic of spermato- and ovogenesis. 61. Fertilization. Biomedical value of a fertilization. Stages. 62. Distant stage of a fertilization. Mechanisms. 63. Contact stage of a fertilization. A synkaryon. The factors ensuring these fertilization’s stage. 64. Concept about types of ovocytes. Features of segmentation of secondary isolecytal ovocytes. 65. Segmentation. Definition. Type of segmentation of the human germ.

66. Embryo changes during segmentation. Terms in embryogenesis. A constitution of a germ at this stage. 67. Implantation. Its stages. A role of an implantation to the hegm development. 68. Implantation. A possible pathology of this period. A human germ at the stage of an implantation. Approximate terms. 69. Gastrulation. Give definitions to this process. Mechanisms of a gastrulation. 70. Derivation of two germinal leyers. Mechanisms derivative, terms. A constitution of a germ at the end of stage. 71. Derivation of three germinal leyers. Mechanisms derivative, terms. A constitution of a germ at the end of stage. 72. Neurulation. Mechanisms derivative, terms. A constitution of a germ at the end of stage. 73. Segmentation of mesoderm. Mechanisms derivative, terms. A constitution of a germ at the end of stage. 74. Derivation of a truncal tuck and isolation of the germ body from extragermal organs and shells. 75. Provisional organs of the human embryo. Classification and functional value. 76. Alantois. Its derivation and functional value for the human embryo. 77. Yolk-sac. Its derivation and functional value for the human embryo. 78. Umbilical cord. Its derivation and functional value for the person. 79. Amniotic shell. Its derivation and functional value for the person. 80. Chorial shell. Structural components. Its derivation and functional value for the person. 81. Decidua. Structural components. Its derivation and functional value for the person. 82. Constitution of a fetus egg wall. Its features in the field of a placental site. 83. Communication of a human germ with an mother’s organism. 84. Placentation as the critical period in germ’s development. Terms, possible pathology of this period. 85. Placenta: the type, моrfo-functional characteristic, development in embryogenesis. 86. Endocrine function of the placenta. Physiological value of chorionic gonadotropinum. 87. Constitution of structurally functional unit of a placenta. Concept about primary, secondary and tertiary villies. 88. Effect external- and internal factors on development of fetus. Critical periods of embryonic development of the human. 89. Polyfetal pregnancy. Reasons, possible consequences. 90. Proliferation and differentiation, their interaction during development of a germ. 91. Embryonic induction as one of regulating mechanism of embryogenesis.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 10 TISSUES EPITHELIUM Course 1

Faculty Medical The contents of the topic: Classification of epithelial tissues 1. Lining and covering epithelia Form the boundary between external environment and body tissues - Cover body surfaces (e.g., the epidermis of the skin) and lines the lumens of internal organs that open to the exterior of the body, - Line body cavities (e.g., peritoneal cavity) and covers the exterior of organs that project into these cavities, - Line blood and lymph vessels, Cell shape and number of layers correlate with the function of the epithelium. 2.Glandular (secretory) epithelia 1. Develop from a lining or covering epithelium by invagination into the underlying connective tissue 2. Form exocrine and endocrine glands. General features of all epithelial tissues  Highly cellular (sparse intercellular space)  Numerous intercellular junctions for attachment and anchorage  Avascular  High regenerative capacity, especially in epithelial membranes, to replace continual sloughing of cells from free surface  Most rest on a basement membrane.  The basement membrane is composed of a basal lamina and a reticular lamina. - The basal lamina is secreted by the epithelial cells and consists of the lamina lucida and the lamina densa. A similar structure is also present in muscle and nervous tissue, where it is referred to as an external lamina. - The reticular lamina is secreted by fibroblasts located in the underlying connective tissue.

 Functions of the basement membrane - Provides support and attachment for the epithelial cells - Selective diffusion barrier  Free and basal surfaces - Basal surface contacts the basal lamina of the basement membrane. - Free surface interfaces with the external environment or spaces within the body. - Polarity. A polarized cell is one that exhibits contrasting properties or structures on opposite sides of the cell. Because epithelial tissues face a free surface, the function of the apical surface is often very different from that at the base of the cell. This diversification is reflected by the nonhomogeneous distribution of organelles. Lining and Covering Epithelial Tissues METHOD OF CLASSIFICATION Classification by number of layers 1. Simple epithelium  One cell layer thick  All cells rest on the basement membrane (basal surface) and all cells face the free surface. 2. Stratified epithelium  More than one cell layer thick  Only the deepest layer of cells contact the basement membrane and only the superficial-most cells have a free surface.  Named according to the shape of the cells at the free surfaceomit. Classification by shape of surface cells 1. Squamous Cells are much wider than tall, resembling a “fried egg.” Nucleus is highly flattened. 2. Cuboidal  Cells are of equal height and width.

 Nucleus is spherical. 3. Columnar  Cells are much taller than they are wide.  Nucleus is oval shaped, generally located toward the base of the cell. Types of Lining and Covering Epithelium І. Simple epithelial tissues 1.Simple squamous Allows for rapid diffusion across the epithelium Forms the lining of blood vessels, alveoli of the lungs, and internal body cavities

2.Simple cuboidal  Lines and absorbs  Forms the walls of ducts and tubules 3.Simple columnar  Lines and absorbs  Forms the lining of the intestines and gall bladder 4. Pseudostratified  Cells are of various heights. All cells rest on the basement membrane, but only the tallest cells reach the free surface. Variation in height of the cells and the location of nuclei give the appearance of a stratified epithelium. Frequently ciliated.  Provides protection  Forms the lining of much of the respiratory tract and much of the male reproductive system ІІ.Stratified epithelial tissues 1.Stratified squamous  Protects from physical abrasion and prevents desiccation 65

 Types - Nonkeratinized (moist). Lining of wet cavities, including the mouth, esophagus, rectum, and anal canal; surface cells are nucleated and living. - Keratinized (dry). Epidermis of the skin; surface cells are nonliving. 2.Stratified cuboidal/columnar. Lines the larger ducts of exocrine glands. 3.Transitional  Protective function; constructed to expand with distension of the hollow organs it lines  Unique to the urinary system; lines the urinary bladder and ureter Surface Specializations 1. Microvilli  Finger-like extensions from the free surface of the cell, about 1micron in height  Are present in large numbers on each cell and, collectively, are called a brush or striated border  Contain a core of actin microfilaments  Are relatively nonmotile  Increase surface area for absorption  Prominent on cells lining the digestive tract and proximal tubules in the kidney 2. Stereocilia  Large, nonmotile microvilli; not cilia  Contain a core of actin microfilaments  Increase surface area  Present on cells lining the epididymis and ductus deferens in the male reproductive tract 3. Cilia  Multiple hair-like extensions from free surface of the cell; 7–10 microns in height  Highly motile; beat in a wave-like motion  Function to propel material along the surface of the epithelium (e.g., in the respiratory system and the oviduct of the female reproductive system)  Core of a cilium is called the axoneme, in which nine pairs of microtubules surround a central pair of microtubules (9 + 2 arrangement).  The axomene of each cilum originates from a basal body that is located at the apex of the cell and is composed of nine triplets of microtubules. CELL JUNCTIONS 1. Specialized structures of the plasma membrane that:  Attach and anchor cells  Establish apical and basolateral membrane domains by sealing adjacent plasma membranes  Provide channels for ionic and metabolic coupling

2. Not restricted to epithelial cells; cell junctions occur, however, in large number in epithelial tissues to resist the physical forces acting on the cells.

3. Types  Tight junction (zonula occludens)  Belt-like, barrier junction around apex of the cell  Provides close apposition of adjacent plasma membranes and occludes the intercellular space  Functions - Prevents diffusion of material between the intercellular space and the lumen of the organ - Establishes apical and basolateral membrane domains in the cell by preventing the lateral migration of proteins in plasma membrane  Adherent junctions - Attach cells to each other and anchor them to the basal lamina; no fusion of the plasma membrane - Types of adherent junctions  Belt desmosome (zonula adherens). Belt-like junction that encircles the apex of the cell like a barrel strap and is located immediately beneath the zonula occludens; serves to attach adjacent cells together; associated with actin filaments.

 Spot desmosome (macula adherens). Disk-like junctions scattered over the surface of the cell, which are paired with similar structures in adjacent cells; associated with intermediate filaments (e.g., keratin filaments in epithelial cells).  Hemidesmosome. Represent a “half desmosome”; these junctions anchor the basal surface of the cell to basal lamina.  Junctional complex. Consists of the zonula occludens, zonula adherens, and desmosomes; because these structures cannot be resolved as separate structures at the light microscopic level, they appear as a single, bar-shaped, dark region at the apical corners of adjacent cells. The term terminal bar was used by early microscopists to define the zonula occludens and zonula adherens at the light microscopic level.  Gap junction - Gap junctions consist of connexons, six transmembrane proteins clustered in a rosette that defines a central pore. Connexons from adjacent cells abut one another, forming a continuity between cells. - Provides metabolic and electrical continuity (coupling) via the pores between cells GENERAL CONSIDERATIONS 1. Develop from or within a lining or covering epithelium 2. Secretory cells may  Differentiate but remain in the lining epithelium  Invaginate into the underlying connective tissue and remain attached to the lining epithelium  Invaginate into the underlying connective tissue but lose their connection  to the epithelium EXOCRINE VS. ENDOCRINE GLANDS Major classification of glands, which is based on the method by which their secretory product is distributed 1.Exocrine glands  Secretory products are released onto an external or internal epithelial surface, either directly or via a duct or duct system.  Secretory cells display polarized distribution of organelles. 2. Endocrine glands  No ducts; secretory products are released directly into the extracellular fluid where they can affect adjacent cells (paracrine secretion) or enter the bloodstream to influence cells throughout the body (endocrine secretion).  No polarization of organelles, except the thyroid gland and enteroendocrine cells of the digestive tract  Secretory products are called hormones. Methods of Product Release from Glandular Cells

1. Merocrine. Secretory product is released by exocytosis of contents contained within membrane-bound vesicles. This method of release is used by both exocrine and endocrine glands. Examples are digestive enzymes from pancreatic acinar cells and insulin from pancreatic islet cells. 2. Apocrine. Secretory material is released in an intact vesicle along with some cytoplasm from the apical region of the cell. This method of release is used by exocrine glands only. An example is the lipid component of the secretory product of the mammary gland. 3. Holocrine. Entire cell is released during the secretory process. Cells that are released may be viable (oocyte or sperm) or dead (sebaceous glands). This method of release is used by exocrine glands only. 4. Diffusion. Secretory product passes through the cell membrane without the formation of secretory granules. Examples are steroid hormones. This method of release is used by endocrine glands only. TYPES OF SECRETORY PRODUCTS 1.Exocrine glands  Mucus. Thick, viscous, glycoprotein secretion  Secretory cells are usually organized into tubules with wide lumens.  Cytoplasm appears vacuolated, containing mucigen that, upon release, becomes hydrated to form mucus.  Nucleus is flattened and located in the base of the cell.  Serous. Thin, watery, protein secretion  Secretory cells are usually organized into a flask-shaped structure with a narrow lumen, called an acinus.  Cytoplasm contains secretory granules.  Nucleus is round and centrally located in the cell.  Special  Lipid. Oily secretion (sebum) from sebaceous glands and lipid portion of milk from the mammary gland.  Sweat. Hypotonic, serous secretion that is low in protein content.  Cerumen. A waxy material formed by the combination of the ecretory products of sebaceous and ceruminous glands with desquamated epidermal cells in the auditory canal 69

2.Endocrine glands  Protein (e.g., insulin) or amino acid derivatives (e.g., thyroxine)  Steroid (e.g., estrogen and testosterone) CLASSIFICATION OF EXOCRINE GLANDS Unicellular glands. Individual cells located within an epithelium, such as goblet cells that secrete mucus Multicellular glands  Sheet gland. Composed of a surface epithelium in which every cell is a mucus-secreting cell. A sheet gland is unique to the lining of the stomach.  The remaining multicellular glands are classified according to: - The shape(s) of the secretory units:  Presence of tubules only  Presence of acini (singular, acinus) or alveoli (singular, alveolus) (these two terms are synonymous), which are flask-shaped structures  Presence of both tubules and acini - The presence and configuration of the duct  Simple. No duct or a single, unbranched duct is present.  Compound. Branching duct system Classification and types of multicellular glands  Simple tubular. No duct; secretory cells are arranged like a test tube that connects directly to the surface epithelium (e.g., intestinal glands).  Simple, branched tubular. No duct; tubular glands whose secretory units branch (e.g., fundic glands of stomach)  Simple, coiled tubular. Long unbranched duct; the secretory unit is a long coiled tube (e.g., sweat glands).  Simple, branched acinar (alveolar). Secretory units are branched and open into a single duct (e.g., sebaceous glands).  Compound tubular. Branching ducts with tubular secretory units (e.g., Brunner’s gland of the duodenum)  Compound acinar (alveolar). Branching ducts with acinar secretory  units (e.g., parotid salivary gland)  Compound tubuloacinar (alveolar). Branching ducts with both tubular and acinar secretory units (e.g., submaxillary salivary gland)

SPECIAL FEATURES OF SOME EXOCRINE GLANDS 1. Serous demilunes. Consist of a “cap” of serous cells around the end of a mucous tubule; appear half-moon shaped in section 2. Myoepithelial cells. Resemble smooth muscle cells in their fine structure but are of epithelial origin; prominent in sweat and mammary glands, they surround secretory units, lying inside the basement membrane, and aid in the expulsion of secretory products from the gland.

Duct System of Compound, Exocrine Glands 1. Intralobular ducts. Contained within a lobule; simple cuboidal to columnar epithelium 2. Interlobular ducts. Receive numerous intralobular ducts; located in the connective tissue between lobules; stratified columnar epithelium 3. Excretory (main) duct. Macroscopic duct draining the entire gland Structure and site Lined by 71

Intercellular canaliculi (alveolus) Alveolar secretory cells Alveolar lumen (alveolus) Alveolar secretory cells Intercalated duct (intralobular) Squamous or cuboidal epithelium Intralobular duct (intralobular) Cuboidal epithelium Interlobular duct (interlobular septum) Columnar epithelium Lobar duct (interlobar septum) Pseudo-stratified columnar epithelium Final duct (lamina propria of tract) Stratified columnar epithelium ENDOCRINE GLANDS  No ducts; generally cells are not polarized  Occurrence  Unicellular (e.g., enteroendocrine cells of the digestive tract); these cells do show polarity because they are located within an epithelium and secrete away from the free surface of the epithelium.  Small clusters of cells (e.g., islet of Langerhans in pancreas)  Organs (e.g., thyroid gland, adrenal gland)  Secretory cells of multicellular glands are usually arranged as plates or cords. The thyroid gland, where the cells form fluid-filled spheres, is an exception to this pattern.  Highly vascular with fenestrated capillaries  Secretory products are called hormones. Hormones can be:  Derived from amino acids (e.g, thyroxine and epinephrine)  Peptides and proteins (e.g., insulin and oxytocin)  Steroids (e.g., testosterone and cortisol); steroid-secreting cells display mitochondria with tubular cristae and contain large amounts of lipid droplets and smooth endoplasmic reticulum.  Secrete by the merocrine or diffusion methods only

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 11 BLOOD AND LYMPH Course 1

Faculty Medical The contents of the topic: ➢ In humans, the average blood volume is 5 liters, constituting 7% of the body mass. ➢ Blood is a specialized connective tissue consisting of cells and cell fragments (46% of blood volume) floating in a unique liquid extracellular matrix (54% of blood volume). ➢ Components  Cells and cell fragments 1. Red blood cells (erythrocytes, RBCs), produced in the bone marrow 2. White blood cells (leukocytes, WBCs), produced in the bone marrow; some lymphocytes are also produced in lymphoid tissues and organs. 3. Platelets. Cell fragments derived from megakaryocytes in the bone marrow; contain granules and function in blood coagulation; 150,000– 450,000 per microliter blood  Plasma. Constitutes the extracellular matrix of blood 1. Composed of 90% water and 8–9% protein. Plasma proteins contains fibrinogen, a fiber precursor protein, which is converted into fibrin when blood clots. 2. Serum. Yellowish fluid remaining after blood has clotted. RED BLOOD CELLS

➢ Cells resemble bi-concave discs, 6–8 microns in diameter; 4–6 million per microliter of blood ➢ Cells are non-nucleated. Cytoplasm contains hemoglobin and cytoskeletal elements but lacks other organelles. ➢ Transport oxygen and carbon dioxide 1. Comprise a flexible membrane enclosing haemoglobin (iron-porphyrin- protein) in a closely packed state which, with membrane-spectrin-actin interactions, maintains the RBC's optimal shape for gas exchanges involving the haemoglobin. 2. Osmolarity of the plasma affects the shape of an RBC. Hypertonic solutions in vitro cause crenation and shrinkage; hypotonic, swelling and haemolysis. 3. Globin is acidophilic, and RBCs stain orange with eosin. 4. Mature RBCs have no nucleus, Golgi body, ER, ribosomes or mitochondria. 5. RBCs do have glycolytic enzymes and substrates, and methaemoglobin reductase and carbonic anhydrase for their respiratory function: 73

o (a) Oxygen binds to ferrous iron of haemoglobin (RBC) for transport: air --> lungs --> blood --> tissues o (b) Carbon dioxide leaves bicarbonate of the plasma and carbaminohaemoglobin (RBC) for transport: tissues --> blood --> lungs --> air 6. Reticulocyte/polychromatophil erythrocyte. Immature RBC, when stained supravitally with cresyl blue, has a blue condensed network of clumped, residual ribonucleoprotein not yet used for protein (globin) synthesis. 7. Life in circulation is estimated by 51Cr labelling at around 120 days, and then the RBC is sequestered in the spleen, liver or bone marrow to be phagocytosed by macrophages. The spleen is most responsible. The volume of RBCs as a percentage of centrifuged whole blood - the haematocrit - is a quick, crude measure of the O2-carrying quality WHITE BLOOD CELLS ➢White blood cells are transported in the blood and migrate through vessel walls (diapedesis) to become active in connective tissues; 5–10 thousand per microliter of blood. ➢ Granular leukocytes  Neutrophil (polymorphonuclear leukocyte, PMNs) 1. 46–81% of circulating WBCs 2. Spherical cell, 12–15 microns in diameter; pale or unstained cytoplasmic granules; heterochromatic nucleus with three to five lobes 3. Move from the blood to sites of infection 4. Phagocytose bacteria and debris  Eosinophil 1. 1–3% of circulating WBCs 2. Spherical cell, 12–15 microns in diameter; cytoplasmic granules stain with eosin; bi-lobed nucleus 3. Move from the blood to sites of infection 4. Secrete proteins cytotoxic to parasites, neutralize histamine, and internalize antigen-antibody complexes  Basophil 1. <1% of circulating WBCs 2. Spherical cell, 12–15 microns in diameter; cytoplasmic granules stain dark blue with hematoxylin; S-shaped nucleus 3. Similar to mast cells; participate in the hypersensitivity reaction by secreting histamine and heparin

➢ Agranular leukocytes  Lymphocyte 1. 24–44% of circulating WBCs 2. Spherical cell, 6–8 microns in diameter; scant cytoplasm and a round heterochromatic nucleus often with a small indentation 3. T and B lymphocytes 4. T lymphocytes. Originate in the bone marrow and mature in the thymus; provide cell-mediated immunity 5. B lymphocytes. Originate in the bone marrow and are carried in the blood to lymphoid tissues and organs, where they become activated and proliferate, transform into plasma cells in connective tissue, and provide humoral immunity by secreting antibodies  Monocyte 1. 3–7% of circulating WBCs 2. Large spherical cells, 12–18 microns in diameter; abundant cytoplasm stains gray-blue; large, U-shaped, euchromatic nucleus 3. Enter connective tissue, where they transform into macrophages; function in phagocytosis and antigen presentation

 Platelets 1. Haemocytoblast enlarges to become a megakaryoblast.

2. The nucleus experiences several rounds of DNA replication, but each time with reassembly of a single nuclear envelope and no segregation into separate nuclei. Thus the nucleus takes on a distinctive lumpy, polyploid form. (The single, large, lumpy nucleus is the criterion for distinguishing megakaryocytes from nearby osteoclasts in bone sections.) 3. Fine cytoplasmic azurophil granules accumulate as the cell becomes a very large granular megakaryocyte. 4. Many paired membranes of smooth ER (demarcation membranes) appear and contribute plasmalemma to the formation of 5. pseudodopodia, which are extended into the lumen of a sinusoid, where they cast off in the blood as platelets. 6. Megakaryocyte cytoplasm might also serve as a transcellular migration pathway for some new leucocytes passing from the marrow into the blood.

Hemogramm reflects contents of separate formed elements per 1 ml of blood. 1. Erythrocytes 3, 7 - 4, 9 million / ml in women 3,9 – 5,5 million / ml in men. 2. Leukocytes - 6000 – 9000 / ml. 3. Platelets - 200 000 – 400 000 / ml. Leukocytic formulareflects percent correlation of different types of leukocytes in the blood (total quantity of leukocytes is accepted for 100%). a. Neutrophils constitute 65 - 75 %: i. young – 0,5 % ii. band cells – 1-6 % iii. mature cells – 47-72 %, b. Eosinophils constitute 1 - 5 %, c. Basophils constitute 0 - 1 %, d. Lymphocytes constitute 19 - 37 %, e. Monocytes constitute 3 -8 %. Age changes of blood 1. Number of erythrocytes at newborn makes 6-7 million / ml. 76

2. By 14th day it is equal to the indexes of the grown man. 3. On 3-6th months there is physiological anaemia ( decrease of number of erythrocytes and hemoglobin). It is related to the transfer of the growth factor of erythrocytes (erythropoietin) synthesis from the liver to kidneys. Age changes of blood 1. The number of leukocytes at new-born makes 10000-30000 / ml. 2. In this period leukocytic formula is similar to such as at adult (neutrophils - ~ 65%, lymphocytes - ~ 25%). 3. Further the number of neutrophils begins to decrease, and lymphocytes – to increase. 4. On 4-5 day the percentage of neutrophils and lymphocytes becomes identical (~ 45%). 5. The process of decrease of number of neutrophils and growth of number of lymphocytes proceeds 1-2 years, when child’s leukocytic formula is stabilized (65% of lymphocytes and 25% of neutrophils). 6. In a subsequent period number of lymphocytes begins to decrease, and neutrophils – to increase. 7. By 4 years their percentage is again evened (~ 45%). 8. By 14-15 years leukocytic formula becomes such, as at adult. Lymph is a rather yellow liquid in lymphatic vessels. Lymph consists of: 1. plasma and 2. formed elements. Lymph contains the same proteins as in plasma of blood, but in smaller amounts. Formed elements of lymph There are 2000-20000 formed elements / mLof lymph. Cell composition of lymph: 1. Lymphocytes constitute 90%; 2. Monocytes constitute 5%; 3. Eosinophils constitute 2%; 4. Neutrophils constitute 1%; 5. Other cells constitute 2%. There are platelets and fibrinogen, therefore lymph is capable of coagulation.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 12 HAEMOCYTOPOIESIS Course 1

Faculty Medical The contents of the topic: ➢ General considerations  Hematopoiesis is the process of blood cell formation, beginning with a pleuripotential stem cell that subsequently goes through a series of cell divisions and differentiations to produce all the mature blood cells.  Postnatal hematopoiesis occurs in red bone marrow located in the spongy bone region of long bones, vertebra, ribs, sternum, and skull. Lymphocytes are also generated in lymphoid organs and tissues.  Blood cells have a relatively short life span and, therefore, new cells are formed continuously.  Precursor cell lineage 1. Stem cells. Pleuripotential cells that give rise to all the blood cells; divide both to renew their own cell population as well as to form progenitor cells, thus beginning the process of blood cell formation. 2. Progenitor cells. Less potentiality than stem cells; committed to the formation of just one or two blood cell lines; have high mitotic activity, dividing to reproduce self and to from precursor cells. 3. Precursor or blast cells. Begin morphologic differentiation; display characteristics of the mature blood cells they will form; not selfrenewing. Mature blood cells. Form after several cell divisions of the precursor or blast cells ➢ Erythropoiesis. Formation of erythrocytes  Process that results in a non-nucleated cell filled with hemoglobin and specialized for transporting respiratory gases  Stages. Cells listed in the order in which they form 1. Proerythroblast. Precursor cell 2. Basophilic erythroblast. Increased numbers of polyribosomes for hemoglobin production result in strong cytoplasmic basophilia; nucleus condenses. 3. Polychromatophilic erythroblast. Number of polyribosomes is reduced as hemoglobin accumulates in the cytoplasm. 4. Orthochromatophilic erythroblast. Continued condensation of the nucleus; increased eosinophilia of the cytoplasm due to accumulating hemoglobin 5. Reticulocyte. Extrusion of the nucleus; small number of polysomes remains.

6. Mature erythrocyte ➢ Granulopoiesis. Formation of granulocytes  Process by which cells first produce lysosomal granules and then synthesize granules containing proteins specific for each granulocytic cell type. Although the term “granule” is commonly used to describe these structures, they are bounded by a unit membrane.  Stages. Cells listed in the order in which they form 1. Myeloblast. Precursor cell 2. Promyelocyte. Production of azurophilic (blue) granules that contain lysosomal enzymes 3. Myelocyte. Nuclear condensation and the appearance of cell-specific granules containing proteins unique for each of the granular leukocytes 4. Metamyelocyte. Cell-specific granules continue to accumulate and the nucleus changes morphology to resemble that of the mature cell. Following the metamyelocyte, an additional stage, called a band cell, occurs in all granulocytes but is most prominent in the neutrophilic lineage. 5. Mature neutrophils, eosinophils, and basophils

➢ Monocytopoiesis. Formation of monocytes 1. Monoblast. Precursor cell 2. Promonocyte. Large cell, up to 18 microns in diameter; nucleus becomes indented and the cytoplasm is basophilic with numerous fine azurophilic granules (lysosomes). 3. Mature monocyte ➢ Lymphocytopoiesis. Formation of lymphocytes 1. Lymphoblast. Precursor cell 2. Pro-lymphocytes. Reduction in size from lymphoblast; some remain in the bone marrow to produce B lymphocytes, others leave the bone marrow and travel to the thymus, where they complete their differentiation into T lymphocytes. 80

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 13 CONNECTIVE TISSUES Course 1

Faculty Medical The contents of the topic: CLASSIFICATION OF CONNECTIVE TISSUE Connective Tissue Proper ➢ Loose (areolar)  Highly cellular, numerous cell types present  Fewer and smaller caliber collagen fibers compared with dense  Abundant ground substance, allows for diffusion of nutrients and wastes  Highly vascularized  Provides padding between and around organs and tissues

➢ Dense  Fewer cells, mostly fibroblasts  Highly fibrous with larger caliber collagen fibers, provides strength  Minimal ground substance  Poorly vascularized  Types - Dense, irregular connective tissue. Fiber bundles arranged in an interlacing pattern; forms the capsule of organs and the dermis of the skin - Dense regular connective tissue. Parallel arrangement of fiber bundles; restricted to tendons and ligaments

➢ Composition 1. Cells. Each type of connective tissue has it own characteristic complement of one or more of a wide variety of cells. 2. Extracellular matrix. Synthesized and secreted by resident “blast” cells specific for each connective tissue type (e.g., fibroblasts and chondroblasts); the matrix is composed of:  Fibers. Collagen, elastic and reticular  Ground substance. An amorphous substance that can exist as a liquid, gel, or flexible or rigid solid, conferring unique structural properties to each connective tissue. ➢ Functions  Provides substance and form to the body and organs  Defends against infection  Aids in injury repair  Stores lipids  Provides a medium for diffusion of nutrients and wastes  Attaches muscle to bone and bone to bone ➢ Types of connective tissue. Classified by the relative abundance, variety, and content of their components  Connective tissue proper  Cartilage  Bone  Special. Includes adipose, elastic, reticular, and mucoid connective tissues as well as blood and hematopoietic tissue THE CONNECTIVE TISSUES: CONNECTIVE TISSUE PROPER ➢ Connective tissue proper comprises a very diverse group of tissues, both functionally and structurally.  Structural functions of connective tissue proper 1. Forms a portion of the wall of hollow organs and vessels and the stroma of solid organs 2. Forms the stroma of organs and subdivides organs into functional compartments 3. Provides padding between and around organs and other tissues 82

4. Provides anchorage and attachment (e.g., muscle insertions)  Provides a medium for nutrient and waste exchange  Lipid storage in adipocytes  Defense and immune surveillance function via lymphoid and phagocytic cells ➢ All connective tissues are composed of two basic components, which vary widely among different types of connective tissue. The components of connective tissues are: 1. Cells (e.g., fibroblasts and macrophages) 2. Extracellular matrix  Fibers (e.g., collagen and elastic fibers)  Ground substance CELLS OF CONNECTIVE TISSUE ➢ Connective tissue cells can be subdivided into two major groups. Resident cells are derived from mesenchyme and are continuously present in the tissue (e.g., fibroblasts and adipocytes). Migratory cells enter and leave the blood stream to migrate through and function in connective tissues (e.g., neutrophils and macrophages [monocytes]). ➢Mesenchymal cell 1. Has a similar appearance to a small, young fibroblast, but is far more multipotential in what cell types it can turn into. 2. In adult tissues, two views are: o a few are present and can explain such findings as the formation of ectopic (out of its expected place) bone in soft CT, otherwise difficult to account for unless differentiated cells such as fibroblasts can dedifferentiate and change their role; o mesenchymal cells all differentiate early in life and thereafter are not present, and fibroblasts or other cells can de- and redifferentiate and become osteoblasts.

➢ Fibroblasts  Synthesize and maintain fibers and ground substance  Major resident cell in connective tissue proper  Active and inactive fibroblasts - Active fibroblast 1. Large, euchromatic, oval nucleus 2. Cytoplasm not usually visible but contains abundant rough endoplasmic reticulum and Golgi 3. Elongated, spindle-shaped cells 4. High synthetic activity - Inactive fibroblast 1. Small, heterochromatic, flattened nucleus 2. Reduced cytoplasm and organelles 3. Low synthetic activity ➢ Macrophages

 Derived from blood monocytes; monocytes enter connective tissue from the bloodstream and rapidly transform into macrophages that function in phagocytosis, antigen processing, and cytokine secretion.  Comprise the mononuclear phagocyte system of the body; include Kupffer cells in the liver, alveolar macrophages in the lung, microglia the central nervous system, Langerhan’s cells in the skin, and osteoclasts in bone marrow  Structure 1. Heterochromatic, oval nucleus with an indentation in the nuclear envelope and marginated chromatin 2. Cytoplasm usually not visible unless it contains phagocytosed material ➢ Mast cells  Mediate immediate hypersensitivity reaction and anaphylaxis by releasing immune modulators from cytoplasmic granules, in response to antigen binding with cell surface antibodies  Structure 1. Round to oval-shaped cells 2. Round, usually centrally located nucleus 3. Well-defined cytoplasm filled with secretory granules containing immune-modulatory compounds (e.g., histamine and heparin) ➢ Plasma cells  Secrete antibodies to provide humoral immunity  Derived from B-lymphocytes  Structure 1. Oval-shaped cells 2. Round, eccentrically located nucleus with heterochromatin clumps frequently arranged like the numerals on a clock-face 3. Basophilic cytoplasm due to large amounts of rough endoplasmic reticulum 4. Well-developed Golgi complex appears as a distinct, unstained region in the cytoplasm near the nucleus and, for that reason, is often referred to as a “negative Golgi.” ➢ Adipose cells (adipocytes, fat cells)  Store lipids  Types - Yellow fat (unilocular) 1. Each cell contains a single droplet of neutral fat (triglycerides) for energy storage and insulation. 2. Minimal cytoplasm, present as a rim around the lipid droplet 3. Flattened, heterochromatic, crescent-shaped nucleus that conforms to the contour of the lipid droplet

4. Can occur singly, in small clusters or forming a large mass, which is then referred to as adipose connective tissue - Brown fat (multilocular) 1. Cells contain numerous, small lipid droplets. 2. Large numbers of mitochondria 3. Present mostly during early postnatal life in humans, abundant in hibernating animals for heat production ➢ White blood cells (WBCs, leukocytes) These cells enter and leave the blood stream to migrate through, and function in, connective tissues. The most common WBCs encountered in connective tissue proper are lymphocytes, neutrophils, and eosinophils. For a complete discussion of blood cells 1. Lymphocytes (T and B lymphocytes)  Small spherical cells with sparse cytoplasm and a round heterochromatic nucleus, often with a small indentation  B cells enter connective tissue where they transform into plasma cells and secrete antibodies. T cells are primarily  located in lymphatic tissues and organs; however, T cells can be present in connective tissue proper under certain circumstances (e.g., organ transplantation). 2. Neutrophils (polymorphonuclear leukocytes, PMNs)  Spherical cells with a heterochromatic nucleus with three to five lobes  Pale-staining cytoplasmic granules  Highly phagocytic cells that are attracted to sites of infection 3. Eosinophils  Spherical cells with a bilobed nucleus  Cytoplasmic granules stain intensely with eosin.  Modulate the inflammatory process EXTRACELLULAR MATRIX ➢ Fibers Fiber type Composition Properties Collagen Collagen I, II Inelastic, eosinophilic Reticular Collagen III Inelastic, branched, argyrophilic Elastic Elastin Elastic, eosinophilic

1. Collagen fibers  Tropocollagen - Basic collagen molecule consisting of three alpha subunits intertwined in a triple helix; collagen types are distinguished by their subunit composition. - Produced by fibroblasts and other matrix-forming cells - Secreted into the matrix, where they spontaneously orient themselves into fibrils with a 64-nm repeating banding pattern

 Major collageen types - Type I. Fibrils aggregate into fibers and fiber bundles; most widespread distribution; “interstitial collagen.” - Type II. Fibrils do not form fibers; present in hyaline and elastic cartilages - Type III. Fibrils aggregate into fibers; present surrounding smooth muscle cells and nerve fibers; forms the stroma of lymphatic tissues and organs - Type IV. Chemically unique form of collagen that does not form fibrils; major component of the basal lamina  Elastic fibers - Composed primarily of elastin; produced by fibroblasts - Elastin forms the central amorphous core of the fiber, which is surrounded by microfibrils. - Unique chemical properties of elastin provide for elasticity. - Elastic fibers occur in nearly all connective tissues in varying amounts and are intermixed with collagen fibers. When present exclusively, they constitute elastic connective tissue. - Frequently difficult to differentiate from collagen with conventional stains  Reticular fibers - Collagen type III fibers - Highly glycosylated and stain with silver (argyrophilic) - When they are the major fiber fiber type (e.g., in the stroma of lymphoid organs), they constitute reticular connective tissue. ➢ Ground substance  Functions - Forms a gel-like matrix of variable consistency in which cells and fibers are embedded - Provides a medium for passage of molecules and cells migrating through the tissue - Contains adhesive proteins that regulate cell movements  Components 1.Tissue fluid. Contains salts, ions and soluble protein 2.Glycosaminoglycans (GAGs) - Long, unbranched polysaccharides composed of repeating disaccharide units, which are usually sulfated - Large negative charge of the sugars attracts cations, resulting in a high degree of hydration. The matrix formed ranges from a liquid passageway to a viscous shock absorber. GAGs are generally attached to proteins to form proteoglycans. 3.Proteoglycan aggregate. Many proteoglycans are attached to hyaluronic acid, which is itself a glycosaminoglycan. 4.Adhesive glycoproteins. For example, fibronectin and laminin. CONNECTIVE TISSUES WITH SPECIAL PROPERTIES

➢ Adipose connective tissue. Consists of accumulations of adipocytes that are artitioned into lobules by septa of connective tissue proper. Provides energy storage and insulation 1. White (unilocular) adipose tissue 1. Comprises primarily fat cells enclosed in basal lamina and held on a framework of reticular fibres in association with many blood capillaries. Fibrous CT encloses the tissue subdividing it with septa. 2. Found subcutaneously in the hypodermis (in the child, a panniculosus adiposus), and in the mesentery, omentum, and retroperitoneal area. Padding fat in palmar, plantar and intraobital sites is not so freely available as an energy store and can survive starvation. Functions - energy store; insulation; padding; steroid conversions. 2. Brown (multilocular) adipose tissue 1. Cells have many separate (multilocular) fat droplets, relatively more cytoplasm, and are smaller than white fat cells. 2. Found around the thorax and kidneys of animals naturally exposed to severe cold, particularly hibernators. 3. Brown fat is a thermogenic organ providing a prompt and direct source of heat to maintain the temperature of vital organs. Uncoupling protein 1 lets mitochondria divert energy in this otherwise unwanted thermal way by uncoupling respiration from ATP formation. 4. Seen in the human newborn; in adults BAT is detectable after adrenergic stimulation. Brown fat might dissipate surplus energy from overeating. ➢ Elastic connective tissue. Regularly arranged elastic fibers or sheets (e.g., the vocal ligament) 1. Elastic fibres or membranes are the predominant element. 2. The fibres may be: o (a) thick or very thick (10-15 µm) and orderly as in the elastic ligaments, e.g., ligamentum nuchae (in the neck of heavy-headed grazing animals), vertebral ligamentum flavum, penile suspensory ligament, and in the vocal chords; or o (b) finer and mixed with membranes in elastic arteries. The lung and airway also have many elastic fibres. o In the ligaments, elastic fibres are formed by fibroblasts and held together by reticular fibres, proteoglycan, and glycoproteins. ➢ Reticular connective tissue. Aloosely arranged connective tissue whose fibers are reticular fibers. Forms the stroma of hematopoietic tissue (e.g., bone marrow) and lymphoid organs (e.g., lymph node and spleen). 1. Has the reticular fibre as the supporting fibre, and phagocytic fixed macrophages. 2. The fibres are made by some of the stellate reticular cells acting as fibroblasts. 3. Reticular tissue also contains parenchymal cells (the main working cells) held by the fibres, e.g., hepatocytes or lymphocytes. 88

➢ Mucoid connective tissue. Embryonic connective tissue with abundant ground substance and delicate collagen fibers; present in the umbilical cord 1. Very rich in proteoglycans and water, has some fine collagen fibres and widely separated young fibroblasts. 2. As Wharton's jelly of the umbilical cord it encloses and cushions the vessels; the ocular vitreous and young dental pulp also fit tolerably well in this class. ➢ Pigment tissue  The pigment connective tissue reminds loose connective tissue, however contains a lot of pigment cells.  Chief distribution: iris, a choroid of an eye.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 14 CARTILAGE TISSUES Course 1

Faculty Medical The contents of the topic: Composition is similar to that of all connective tissues  Cells (chondroblast and chondrocyt)  Extracellular matrix consisting of fibers, ground substance, and tissue fluid ➢ Cartilage is avascular and possesses no lymph vessels or nerves. ➢ Types of cartilage 1. Hyaline. Provides nonrigid support 2. Elastic. Provides support with large amount of flexibility 3. Fibrocartilage. Provides strength under stress COMPONENTS OF CARTILAGE ➢ Perichondrium. Connective tissue surrounding cartilage tissue. Layers include:  Fibrous layer. Outer portion, composed of dense connective tissue, serves as a source of reserve cells for the chondrogenic layer  Chondrogenic layer. Inner, more cellular portion contains chondroblasts and blends imperceptibly into cartilage tissue proper.

➢ Cells  Chondroblasts 1. Lie on the surface of cartilage in the chondrogenic layer of perichondrium 2. Secrete extracellular matrix around themselves, thus becoming chondrocytes  Chondrocytes 90

1. Are chondroblasts that have surrounded themselves with matrix 2. Lie within cartilage in potential spaces called lacunae Secrete and maintain extracellular matrix 3. Are frequently located in isogenous groups, a cluster of chondrocytes, resulting from the proliferation of a single chondrocyte ➢ Extracellular matrix. Both flexible and noncompressible  Composition - Fibers. Collagen fibrils and fibers predominate in hyaline cartilage and fibrocartilage, respectively; elastic fibers predominate in elastic cartilage. - Ground substance. Tissue fluid surrounds proteoglycan aggregates bound to collagen fibers. Collectively, these form a firm gel, which resists compressive forces.  Subdivisions - Territorial matrix immediately surrounds chondrocytes. This matrix stains more intensely with hematoxylin due to the high concentration of proteoglycans. - Interterritorial matrix is the lighter-staining matrix outside the territorial matrix and between isogenous groups. GROWTH OF CARTILAGE ➢ Appositional growth occurs at the surface of cartilage. New cartilage is added (apposed) to the surface of preexisting cartilage by the activity of chondroblasts lying in the chondrogenic layer of the perichondrium. ➢ Interstitial growth occurs from within cartilage tissue. Chondrocytes produce additional matrix and divide, forming isogenous groups. ➢ Hyaline cartilage  Is the most common cartilage type and is hyaline (glassy) in appearance  Contains collagen type II fibers that have the same refractive index as ground substance and, therefore, are not visible with the light microscope by conventional staining methods  Stains blue with conventional dyes, due to the relative abundanceof its ground substance matrix  Possesses numerous isogenous groups  Function and distribution. Forms most of the cartilages of the body, comprises the fetal skeleton, attaches ribs to the sternum, forms epiphyseal plates, and lines articular surfaces. (The lack of a perichondrium on the articular cartilages provides a smooth, glassy articular surface.)

➢ Elastic cartilage  Has a visible network of interlacing elastic fibers in addition to collagen type II fibers  Possesses fewer isogenous groups than does hyaline cartilage  Function and distribution. Pinna of ear, epiglottis, smaller laryngeal cartilages (i.e., present where flexibility and support are necessary)

➢ Fibrocartilage  Is a functional and structural intermediate between hyaline cartilage and the dense connective tissues  Possesses abundant collagen type I fibers, arranged in either a regular or irregular configuration. These collagen fibers cause this cartilage to stain pink with eosin.

 Has minimal ground substance. The ground substance that is present is usually located immediately around the chondrocytes.  Possesses few isogenous groups  Combines great tensile strength with flexibility  Frequently found where a tendon or a ligament attaches to a bone (regular arrangement of fibers)  Located in the pubic symphysis and knee cartilages (irregular fiber arrangement) REGRESSIVE CHANGES IN CARTILAGE ➢ Occur in cartilage more frequently than in many other tissues ➢ Regressive changes also occur in the hyaline cartilage of the epiphyseal plate and represent critical steps in endochondral bone formation. ➢ Stages of regression 1. Chondrocytes hypertrophy and secrete alkaline phosphatase that provides a calcifiable matrix. 2. Calcium phosphate is deposited in the matrix, prohibiting diffusion of nutrients to the chondrocytes. 3. Chondrocytes die, leaving behind empty lacunae and the calcified matrix.

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 15 BONE TISSUE. STRUCTURE Course 1

Faculty Medical The contents of the topic: Bone  Provides structural support, giving shape and form to the body  Provides movement through the insertion of muscles  Serves as a stored source for calcium and phosphate  Contains bone marrow (myeloid tissue) ➢ Histological preparation of bone  Ground bone preparation. Unpreserved bone is ground to a thinness where light can be transmitted through it. Because no preservation has occurred, neither cells nor organic matrix survive.  Decalcified bone. Cells are fixed (preserved) and inorganic matrix removed by decalcification. Good detail of organic matrix (cells, periosteum, etc.) is maintained, but lamellae and inorganic matrix are difficult to distinguish. ➢ Compact bone. Appears as a solid mass to the naked eye, covering the exterior of bones and forming the shaft of long bones. ➢ Spongy or cancellous bone. Gross appearance is like a sponge, with a labyrinth of bony spicules and intervening spaces that are filled with loose connective tissue or red marrow and at least one blood vessel. Spongy bone is located in the interior of bones. ARCHITECTURE OF A LONG BONE ➢ The diaphysis (shaft), composed of compact bone, is hollow and is usually lined by a thin band of spongy bone. ➢ An epiphysis, the knob at either end of the diaphysis, is composed of a thin rim of compact bone. The spongy bone in its interior houses red marrow. ➢ Metaphysis. Flared region between diaphysis and epiphysis. ➢ Epiphyseal plate. Hyaline cartilage separating epiphysis and metaphysis in growing bones. Growth in bone length occurs as hyaline cartilage in the epiphyseal plate goes through various stages of regression, providing a framework on which bone is deposited. When the hyaline cartilage in the epiphyseal plate is exhausted, growth stops. The epiphysis and metaphysis fuse in the adult, leaving an epiphyseal line as a remnant of the epiphyseal plate. ➢ Marrow

 Red marrow, found in all bones of the fetus, is restricted to spongy bone areas of selected bones in the adult and contains hematopoietic tissue that forms blood cells.  Yellow marrow, found in the shafts of long bones in the adult, consists mainly of adipose connective tissue that retains the potential to become red marrow under hemorrhagic stress. ➢ Articular cartilage is composed of hyaline cartilage and covers articular surfaces of bone. This cartilage does not possess a perichondrium; the glassy, smooth cartilage provides a good articulating surface. COMPONENTS OF BONE ➢ Extracellular matrix  Organic portion, osteoid. Secreted by osteoblasts - Collagen type I fibers comprise the majority of the organic matrix. Their predominance causes bone to stain pink with eosin. - Ground substance is minimal, composed of glycosaminoglycans such as chondroitin sulfate, keratan sulfate, and some glycoproteins that avidly bind calcium.  Inorganic portion. Calcium and phosphate, in the form of hydroxyapatite crystals, are deposited along the collagen fibrils and form 50% of the dry weight of bone. This ossified matrix renders bone impermeable to diffusion of nutrients and requires that bone be well vascularized. ➢ Cells  Osteoblasts 1. Located on all exterior surfaces of bone as the innermost portion of the periosteum or in the endosteum lining all interior bony surfaces 2. Inactive osteoblasts are flattened cells with heterochromatic nuclei. 3. Active osteoblasts are stellate and contain organelles necessary for protein, primarily collagen, production. These cells synthesize high levels of alkaline phosphatase. 4. Function to synthesize bone 5. Secrete osteoid first. In the presence of alkaline phosphatase, osteoblasts facilitate the deposition of calcium phosphate, thus mineralizing the osteoid.  Osteocytes 1. Are osteoblasts that have completely surrounded themselves by bony matrix and, therefore, must lie within, rather than on, bone tissue. These flattened, inactive cells lie in lacunae (spaces) in the bone and extend long processes from the cell body. These processes lie in narrow tunnels called canaliculi and connect, via gap junctions, with adjacent osteocytes and/or osteoblasts at the bone surface. 2. Function to transport materials between blood and bone and to maintain surrounding matrix; they do not divide or secrete matrix.

 Osteoclasts 1. Are large cells with 15–20 or more nuclei and vacuolated, frothy cytoplasm. A ruffled border, the highly enfolded cell membrane facing the bone, is the site of bone resorption. 2. Are located on internal surfaces as part of the endosteum or on external surfaces as part of the osteogenic layer of the periosteum. 3. Osteoclasts lie in depressions in the bone, Howship’s lacunae, which form as osteoclasts resorb bone. 4. Resorb bone via the acid phosphatase and proteolytic enzymes they secrete ➢ Surface coverings  Periosteum. Double layer of connective tissue surrounding the outer surface of bones, except for articular surfaces Layers 1. Fibrous layer. Outer layer of dense connective tissue that serves as a reserve-cell source for the osteogenic layer 2. Osteogenic layer. Inner, more cellular layer, contains osteoblasts and osteoclasts. Site of bone deposition and resorption, respectively. 3. Well vascularized and richly innervated  Endosteum 1. Is composed of a single row of osteoblasts, osteoclasts, and/or osteo- progenitor cells that lines all interior surfaces of bone except for lacunae and canaliculi 2. Serves as a means of bone growth and/or resorption Microscopic Appearance of Bone (Related to the Age of a Bone)

➢ Woven or immature bone is the first bone deposited.  May be either spongy or compact  Referred to as woven bone because fibers are deposited in a random array  Contains osteocytes that are more numerous and spherical than those of lamellar bone. These osteocytes are not in any orderly arrangement.  Is less well mineralized than lamellar bone and, therefore, appears bluer than lamellar bone with hematoxylin and eosin stains  Is usually resorbed and replaced by lamellar bone ➢ Lamellar or mature bone  Replaces most woven bone or may be deposited de novo  May be either spongy or compact  Is referred to as lamellar bone because the matrix is deposited in layers or lamellae  Fibers are deposited in parallel array within a lamella.  Osteocytes are fewer and flatter than those in woven bone and are organized in rows between the lamellae.  Better mineralized than woven bone  Bone is not a static structure and is constantly being resorbed and reconstructed. Therefore, lamellar bone is also resorbed and reconstructed throughout life.

ARCHITECTURE OF ADULT, COMPACT LAMELLAR BONE ➢ Outer circumferential lamellae. Stacks of lamellae extend at least partially around the outer circumference of a long bone. Deposition of these lamellae by the periosteum results in increased thickness in the wall of the diaphysis. ➢ Inner circumferential lamellae. Stacks of lamellae extend at least partially around the inner circumference of a long bone facing the marrow cavity. Deposition of these lamellae by the endosteum results in increased thickness of the wall of the diaphysis. ➢ Haversian systems, osteons  Primary structures of compact lamellar bone  Cylinders of concentric lamellae, deposited by endosteum, that run parallel to the long axis of a bone  Composition - Central Haversian canal 1. Appears round in cross-section with a smooth periphery 2. Contains a blood vessel(s) and loose connective tissue 3. Is lined with an endosteum - Concentric lamellae (4–20) surround the Haversian canal.

1. Collagen fibers are in parallel alignment within a single lamella, wrapping helically around the Haversian canal. 2. Pitch of the helix varies with each lamella in the osteon.  Provides great strength to a long bone  An osteon is formed by the centripetal deposition of the concentric lamella (i.e., outer lamella is the oldest).

➢ Additional lamellae/structures associated with adult, compact lamellar bone  Interstitial lamellae. Portions of Haversian systems that remain after resorption of the rest of the osteon. These lamellae are interposed between other, complete Haversian systems.  Volkmann’s canals. Channels oriented perpendicularly between adjacent Haversian canals, interconnecting these canals with each other and with the surfaces of bone. Volkmann’s canals contain blood vessels that transport blood from the surface of bone to blood vessels within Haversian canals.  Cement lines. Thin, refractive lines that are collagen poor and stain, therefore, with hematoxylin. Cement lines are located: 1. Around Haversian systems, demarcating where resorption stopped and the formation of a new osteon began 2. Beneath and between circumferential lamellae, denoting where deposition of lamellae halted for a period of time and then began again

Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 16 BONE TISSUE.DEVELOPMENT Course 1

Faculty Medical The contents of the topic: BONE GROWTH ➢ New, adult bone is always laid down on preexisting bone or cartilage. ➢ Bone growth is always appositional, with either endosteum or periosteum laying down lamellae of bone. Interstitial growth is impossible in bone because its rigid, ossified matrix does not allow osteocytes to secrete additional matrix or to divide. BONE DEPOSITION ➢ Newly deposited bone assumes the shape of the bone or cartilage on which it is deposited ➢ In spongy, lamellar bone, new lamellae are laid down by osteoblasts in the endosteum located at the periphery of each trabecula, thus increasing its thickness. ➢ In compact lamellar bone, new lamellae are laid down either as outer circumferential lamellae by osteoblasts in the periosteum or as inner circumferential lamellae and Haversian systems (osteons) by the endosteum. BONE RESORPTION ➢ Removal of bone by osteoclasts for remodeling during growth and/or to mobilize calcium throughout life ➢ Resorption process  Osteoclasts on the periosteal and endosteal surfaces resorb bone from bone surfaces.  Resorption canal 1. Is a cylindrical, longitudinal tunnel formed as compact bone on the interior of bone is resorbed 2. Appears in cross-section as an irregularly shaped, bony surface lined with an endosteum containing osteoclasts 3. Usually extends past cement lines, eroding through portions of several osteons. Therefore, remnants of resorbed osteons may surround the resorption canal. 4. Is not lined by concentric lamellae as are osteons 5. When resorption stops, osteoblasts begin filling in a resorption canal by centripetal (from outside to inside) deposition of new lamellae, forming a new osteon. The newest lamella of this secondary osteon is the one adjacent to the Haversian canal.

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6. Remains of partially resorbed Haversian systems around this secondary osteon are called interstitial lamellae.

BONE FORMATION (OSSIFICATION) Intramembranous Bone Formation ➢ Definition. Bone formation by a connective tissue membrane. No cartilage precedes this bone formation. Bone formed may be woven or lamellar, spongy or compact. ➢ Connective tissue membranes involved in intramembranous ossification include mesenchyme in the fetus and periosteum or endosteum in both the fetus and the adult. ➢ Occurrence of intramembranous bone  Bone laid down by mesenchyme forming the flat bones of the skull and part of the mandible  Bone laid down by the periosteum or endosteum ➢ Types of intramembranous ossification 1. Ossification from mesenchyme in the fetus - Mechanism of ossification 1. Mesenchymal cells cluster and differentiate into osteoblasts that secrete organic matrix (osteoid) around themselves. This matrix becomes mineralized, thereby forming bone. 2. Bone formed is woven, spongy bone. - Many areas of this spongy, woven bone are converted to compact, lamellar bone by the filling in of the spaces between trabeculae with osteons. - Other areas of this spongy bone are not converted to compact, however, such as the spongy bone forming the diploe of flat bones of the skull.

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2. Ossification from a connective tissue membrane, such as periosteum or endosteum - Mechanism of ossification. Osteoblasts in the endosteum or in the osteogenic layer of the periosteum secrete and lay down lamellae of bone. - Lamellae conform to the shape of the bone or cartilage on which they are deposited: 1. Lamellae deposited around a cylindrical cavity form an osteon. 2. Circumferential lamellae form on the inner and outer surfaces of bone from the endosteum or periosteum, respectively. 3. Endosteum adds lamellae to trabeculae of spongy bone. Endochondral Bone Formation ➢ Formation of bone by replacement of a preexisting hyaline cartilage template. The cartilage must first undergo regressive changes that produce a framework upon which bone is deposited (ossification). ➢ Bones formed endochondrally include bones at the base of the skull, long bones, vertebrae, pelvis, ribs. ➢ Events occurring before ossification begins Hyaline cartilage template of the future bone is formed in the fetus. This cartilage is surrounded by a perichondrium and enlarges by appositional and interstitial growth as the fetus grows.  Regressive changes begin in cartilage cells in the central, diaphyseal region of the template at what will become the primary center of ossification.

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 Chondrocytes mature, greatly hypertrophy at the expense of surrounding matrix, and begin to secrete alkaline phosphatase.  The presence of alkaline phosphatase leads to the calcification of the cartilage matrix, making it impermeable to metabolites.  Chondrocytes die, leaving behind their lacunae separated by spicules of calcified cartilage matrix. The oxygen supply to the fetus is increasing as the fetal circulatory system becomes functional, supplying blood to the hyaline cartilage template of the future bone. ➢ Stages of ossification  Formation of a periosteal band or collar 1. Around the middle of the shaft of the cartilage template, the chondroblasts differentiate into osteoblasts and begin secreting a bony, rather than a cartilaginous, band called the periosteal band or collar. This cylinder of bone is formed by intramembranous ossification because it does not replace cartilage that has gone through regressive changes. The perichondrium surrounding the periosteal collar is now called a periosteum.

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2. The remainder of the cartilage template is surrounded by a perichondrium.  Primary center of ossification  One of the fetal arteries, called the periosteal bud, and its surrounding mesenchymal cells, penetrate the diaphyseal region of the cartilage template into the area of the degenerating calcified cartilage.  Mesenchymal cells accompanying the artery differentiate into osteoblasts that deposit bone on the spicules of the calcified cartilage framework. Resulting spicules consist of: 1. A core of calcified cartilage that stains blue with hematoxylin 2. An outer perimeter of woven bone that stains pink with eosin  Some of the spicules of cartilage and bone are resorbed to form the future marrow cavity.  This cartilage degeneration–bone deposition process continues toward either epiphysis, becoming more organized into discrete zones, and forming the epiphyseal plate. 1. Resting zone of “normal” hyaline cartilage 2. Zone of proliferation where isogenous groups of chondrocytes actively divide, forming linear isogenous groups. This zone maintains cartilage thickness. 3. Zone of maturation and hypertrophy of chondrocytes, with the production of alkaline phosphatase, and the subsequent calcification of the cartilage matrix 104

4. Zone of degeneration where chondrocytes die, leaving empty lacunae surrounded by vertically oriented spicules of calcified cartilage 5. Zone of ossification where bone is deposited on calcified cartilage spicules 6. Zone of resorption where calcified cartilage–bone spicules are resorbed to form the marrow space  Secondary center of ossification occurs in each epiphysis; ossification follows a similar pattern as that at the primary center except: 1. No periosteal band is formed. 2. Ossification occurs in a radial manner from the original center of the secondary center of ossification. 3. Bone resorption does not occur; thus, spongy bone permanently fills the epiphyses. 4. Ossification does not replace articular cartilage. ➢ Growth in length continues from epiphyseal plates, which:  Are established by formation of the primary and secondary centers of ossification  Are composed of hyaline cartilage showing the zonations described above  Are located between each epiphysis and metaphysis  Maintain a constant thickness throughout growth due to equivalent activity in the zones of proliferation and resorption  Are depleted at appropriate developmental stages as cartilage proliferation stops and the epiphyseal plate can no longer perpetuate itself. Spongy bone replaces the epiphyseal plate, leaving an epiphyseal line as its remnant. This process is referred to as closure of the epiphyseal plate.

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Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 17 MUSCLE TISSUES Course 1

Faculty Medical The contents of the topic: Muscle tissue is specialized for the ability to shorten or contract. While all cells possess the cellular machinery necessary for shape change and contraction, these structures are significantly more prominent in muscle cells. For some muscle types, the cells are nonproliferative due to this high degree of specialization and differentiation. ➢ Muscle contraction is accomplished by the reciprocating sliding of intracellular filaments composed of actin and myosin. ➢ Muscle tissue comprises the “flesh” of the body and much of the walls of hollow organs. Due to its high degree of specialization, unique terms are used for certain structures in muscle cells.  Individual muscle cells are called muscle fibers.  The cytoplasm of muscle fibers is called sarcoplasm.  The muscle fiber plasma membrane is called the sarcolemma.  The smooth endoplasmic reticulum is called the sarcoplasmic reticulum. CLASSIFICATION OF MUSCLE ➢ Functional classification is based on the type of neural control.  Voluntary  Involuntary ➢ Structural classification is based on the presence or absence of crossstriations.  Striated  Nonstriated (smooth) ➢ Combined functional and structural classification  Skeletal muscle - Striated and voluntary - Found mostly attached to the skeleton Cardiac muscle - Striated and involuntary - Composes the majority of the heart wall (myocardium) Smooth (visceral) muscle - Nonstriated and involuntary - Found mostly in the walls of hollow organs and vessels Skeletal Muscle ➢ Connective tissue investments of a skeletal muscle Function

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- Separate muscle into compartments - Transmit the force of contraction to insertion points Components - Endomysium. Reticular fibers surrounding each muscle fiber plus the external (basal) lamina produced by the muscle fiber - Perimysium. Dense connective tissue surrounding groups of fibers and dividing the muscle into fascicles - Epimysium. Dense connective tissue surrounding the entire muscle, blends with the deep fascia and tendons ➢ Hierarchy of skeletal muscle organization Myofilaments. Visible only with the electron microscope; composed primarily of actin, which forms 5-nm wide thin filaments, and myosin, which forms 15-nm wide thick filaments Myofibrils. Visible with the light microscope, 1–2 microns wide, oriented parallel to the long axis of the cell; composed of bundles of overlapping myofilaments that are arranged in register, producing an alternating light- dark, striated banding pattern

Muscle fiber. Specialized term for a muscle cell, 10–100 microns wide; sarcoplasm is filled with hundreds of myofibrils, which are oriented parallel to each other and to the long axis of the muscle fiber. Muscle fascicle. Collection of muscle fibers surrounded by perimysium; collections of muscle fascicles are surrounded by the epimysium and form a muscle.

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➢ Structure of skeletal muscle fibers  Largest fiber type, fibers can be 1–30mm in length and 10–100 microns in diameter.  Each muscle fiber is cylindrical, unbranched, and multinucleated.  The multiple nuclei are located at the periphery of the muscle fiber immediately beneath the sarcolemma.  Extensive smooth endoplasmic reticulum is called the sarcoplasmic reticulum.  Each fiber is surrounded by an external lamina (basal lamina), which contributes to the endomysium of the muscle fiber.  Fibers can increase in size (hypertrophy) but not in number (hyperplasia).  Fibers show prominent, alternating light and dark bands (crossstriations) due to the alignment and overlap of the myofilaments within myofibrils. Myofilaments within a myofibril are arranged in register and adjacent myofibrils are similarly aligned, causing the banding pattern seen at both the light and electron microscopic levels.

- A band appears dark and contains actin and myosin. - I band appears light and contains actin only. - Z-line, composed of alpha-actinin, is located in the center of the I band. - H band is located in the center of the A band and represents the area where actin is not present. - M band is located in the center of the H band and represents areas of cross- connections between myosin filaments. - Sarcomere 108

 Contractile unit of striated muscle fibers, seen in both skeletal and cardiac muscle fibers  Extends from Z-line to Z-line  Sarcomeres are repeated in series along the length of each myofibril. Adjacent myofibrils maintain the alignment of sarcomeres. - Alterations in sarcomeres during contraction  Sarcomeres shorten.  Z-line interval narrows.  Width of H and I bands decrease as actin is pulled past the myosin.  A band width remains unchanged. ➢ Coordination of skeletal muscle fiber contraction 1. A complex system of intracellular, membranous structures called the triad insures coordinated contraction throughout the muscle fiber by (1) allowing the nervous impulse to penetrate and simultaneously reach all parts of the muscle fiber; and (2) releasing calcium in response to the nervous impulse. These functions are accomplished by the “triad.” 2. Triads. Composed of one T-tubule plus two adjacent terminal cisterns of the sarcoplasmic reticulum  T-tubules are invaginations of the sarcolemma that occur at the junction between A and I bands of the myofibrils.  Terminal cisterns are expanded portions of the sarcoplasmic reticulum that lie adjacent to the T tubule and release calcium to initiate contraction.  Role of triad in muscle contraction Anerve impulse arriving at the muscle fiber depolarizes the sarcolemma at the neuromuscular junction. The membrane depolarization propagates along the sarcolemma and extends down the T-tubules. T-tubule depolarization is transmitted to the terminal cisterns and the remainder of the sarcoplasmic reticulum, causing release of stored calcium. Calcium initiates the interaction between actin and myosin myofilaments, leading to muscle contraction. Calcium is recaptured by sarcoplasmic reticulum during relaxation. ➢ Mechanism of contraction, sliding filament model At regions where actin and myosin myofilaments overlap, release of calcium causes the head groups of myosin to contact the actin filament. Hydrolysis of ATP causes a change in the configuration of the myosin head group, resulting in a sliding of the actin myofilament past the myosin by the ratcheting action of the myosin head groups. Since the actin filaments are anchored at the Z-line, the result of the sliding is shortening of the sarcomere. ➢ Associated structures

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 Neuromuscular junction (motor end plate)  Specialized “synapse” between the terminals of a motor axon and the sarcolemma of a muscle fiber  Motor unit. Consists of the motor neuron, its axon, and all the  muscle fibers it innervates  Proprioceptors  Sensory receptors, encapsulated by connective tissue, serve to regulate muscle tension and tone.  Types - Muscle spindle. Highly modified skeletal muscle fibers, intrafusal fibers, are aligned with and surrounded by normal skeletal muscle fibers. - Golgi tendon organs. Located within tendons CARDIAC MUSCLE ➢ Cardiac muscle occurs only in the myocardium of the heart and, to a variable extent, in the roots of large vessels where they join the heart.

➢ Structure of cardiac muscle fibers  Intermediate in size between skeletal and smooth muscle  Fibers are cylindrical, branch, and form interwoven bundles.  Usually one nucleus per fiber located in the center  Organelles are clustered at the poles of the nucleus.  Myofilament organization into myofibrils is identical to skeletal muscle. Cross-striations and bands identical to skeletal muscle are present, but not as prominent.  Intercalated discs - Junctional complexes that are unique to cardiac muscle fibers - Consist of specialized cell junctions and interdigitations of the sarcolemma at the ends of the fibers - Contain three types of junctions  Fascia adherens. Similar to zonula adherens of epithelia; serve to attach cardiac muscle fibers and anchor actin filaments of the terminal sarcomeres at the ends of the cell. Acts as a hemi-Z-line.

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 Desmosomes. Bind ends of fibers together  Gap junctions. Provide ionic coupling between fibers  High vascularity and with large numbers of mitochondria reflect the high metabolic requirements of cardiac muscle fibers.  Fibers are capable of hypertrophy but not hyperplasia.

➢ Coordination of cardiac muscle contraction  Sarcomeres, myofibrils, and myofilaments are the same as skeletal muscle fibers.  T-tubules are located at the level of the Z-lines, rather than at junction of A and I bands as in skeletal muscle.  No triads. Sarcoplasmic reticulum is not as well developed as in skeletal muscle fibers and does not form terminal cisterns. Contraction is initiated by intracellular calcium release.  Contraction can spread through the myocardium due to the presence of gap junctions that allow calcium to flow from one fiber into another. SMOOTH MUSCLE ➢ Smooth muscle occurs mostly as sheets, which form the walls of most hollow organs with the exception of the heart. Smooth muscle is also prominent in the walls of blood vessels, many respiratory passageways, and some genital ducts.

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➢ Structure of smooth muscle fibers  Smallest fiber type, length varies from 20 microns in blood vessels to 500 microns in the uterus  Unbranched spindle-shaped fibers are elongated with tapering ends and unbranched.  Possess a single, centrally placed, oval nucleus, which can appear spiraled or “inch-worm”–shaped when the fiber is contracted.  Organelles are clustered at the poles of the nucleus.  Nonstriated; no myofibrils are present.  External (basal) lamina is present along with reticular fibers.  Abundant gap junctions  Capable of both hypertrophy and hyperplasia

➢Organization of the contractile proteins  Actin and myosin myofilaments are present, but they are not organized into myofibrils.  Myofilaments overlap as in striated muscle and crisscross throughout the sarcoplasm, forming a reticulum.  Dense bodies - Serve as insertion points for myofilaments to transmit the force of filament sliding - Contain alpha-actinin and, thus, resemble Z-lines of striated muscle - Present in the cytoplasm and associated with the sarcolemma ➢ Coordination of smooth muscle contraction 112

 No T-tubules are present; however, fibers do have a rudimentary sarcoplasmic reticulum.  Sliding filament mechanism. Regulated by intracellular release of calcium but with some differences from striated muscle fibers ➢ Types of smooth muscle  Visceral smooth muscle  Occurs in sheets in the wall of hollow organs (e.g., digestive tract)  Minimally innervated; contraction spreads in peristaltic waves facilitated by large numbers of gap junctions.  Specialized for slow, prolonged contraction

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Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 18 NERVOUS TISSUE. NEUROCYTES AND NEUROGLIA Course 1

Faculty Medical The contents of the topic: Cell Lineages of the Nervous System For the PNS, the problems are: the large number of neural crest-derived cell types, including many non-neural ones (mostly because the crest is the major constructor of the head); that additions are still being made to the list; the evidence is chiefly from birds; and some head structures, e.g., receptors and ganglion neurons for hearing and balance come from ectodermal placodes. In the CNS, the story is coming to resemble that for haematopoiesis, with a multipotent neural stem cell giving rise to a self-propagating progenitor pool. From this pool, self-sustaining populations of neuroblasts and glioblasts derive. Further specifications, under the control of neural 'growth factors', are for transmitter type, shape, and axon length, and for glioblast derivatives, whether to be type 1 or 2 astrocytes, or oligodendrocytes. Microglia are regarded as invaders of haematopoietic origin, but is this true for all of them, always? Other questions are: do neural progenitors live on in the adult CNS? (They are present in olfactory mucosa.). ➢ Nervous tissue is highly specialized to employ modifications in membrane electrical potentials to relay signals throughout the body. Neurons form intricate circuits that (1) relay sensory information from the internal and external environments; (2) integrate information among millions of neurons; and (3) transmit effector signals to muscles and glands. ➢ Anatomical subdivisions of nervous tissue  Central nervous system (CNS)  Brain  Spinal cord  Peripheral nervous system (PNS)  Nerves  Ganglia (singular, ganglion) CELLS OF NERVOUS TISSUE ➢ Neurons.Functional units of the nervous system; receive, process, store, and transmit information to and from other neurons, muscle cells, or glands Composed of a cell body, dendrites, axon and its terminal arborization, and synapses Form complex and highly integrated circuits ➢ Supportive cells  Outnumber neurons 10 : 1 114

 Provide metabolic and structural support for neurons, insulation (myelin sheath), homeostasis, and phagocytic functions  Comprised of astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS; comprised of Schwann cells in the PNS STRUCTURE OF A “TYPICAL” NEURON ➢ Cell body (soma, perikaryon)  Nucleus - Large, spherical, usually centrally located in the soma - Highly euchromatic with a large, prominent nucleolus  Cytoplasm - Well-developed cytoskeleton - Intermediate filaments (neurofilaments) - 8–10 nm in diameter - Microtubules - 18–20 nm in diameter - Abundant rough endoplasmic reticulum and polysomes (Nissl substance) - Well-developed Golgi apparatus - Numerous mitochondria

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➢ Dendrite(s)  Usually multiple and highly branched at acute angles  May possess spines to increase surface area for synaptic contact  Collectively, form the majority of the receptive field of a neuron; conduct impulses toward the cell body

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➢ Organelles  Microtubules and neurofilaments  Rough endoplasmic reticulum and polysomes  Smooth endoplasmic reticulum  Mitochondria ➢ Axon Usually only one per neuron Generally of smaller caliber and longer than dendrites Branches at right angles, fewer branches than dendrites Organelles - Microtubules and neurofilaments - Lacks rough endoplasmic reticulum and polysomes - Smooth endoplasmic reticulum - Mitochondria

 Axon hillock. Region of the cell body where axon originates - Devoid of rough endoplasmic reticulum - Continuous with initial segment of the axon that is a highly electrically excitable zone for initiation of nervous impulse  Usually ensheathed by supporting cells  Transmits impulses away from the cell body to - Neurons - Effector structures. Muscle and glands  Terminates in a swelling, the terminal bouton, which is the presynaptic element of a synapse TYPE OF NEURONS BY SHAPE AND FUNCTION ➢ Multipolar neuron. Most numerous and structurally diverse type 117

 Efferent. Motor or integrative function  Found throughout the CNS and in autonomic ganglia in the PNS ➢ Pseudounipolar neuron  Afferent. Sensory function  Found in selected areas of the CNS and in sensory ganglia of cranial nerves and spinal nerves (dorsal root ganglia) ➢ Bipolar neuron Afferent. Sensory function Found associated with organs of special sense (retina of the eye, olfactory epithelium, vestibular and cochlear ganglia of the inner ear) Developmental stage for all neurons

Group of cell bodies Bundle of processes

Central nervous system Nucleus or cortex (gray Tract (white matter) matter)

Peripheral nervous Ganglion Nerve system ARRANGEMENT OF NEURONAL CELL BODIES AND THEIR PROCESSES ➢ In both CNS and PNS, cell bodies are found in clusters or layers and axons travel in bundles. These groupings are based on common functions and/or common connections. SUPPORTIVE CELLS ➢ Supporting cells of the CNS (neuroglial cells); outnumber neurons 10:1  Astrocytes Stellate morphology - Types  Fibrous astrocytes in white matter  Protoplasmic astrocytes in gray matter - Functions 1. Physical support 2. Transport nutrients 3. Maintain ionic homeostasis 4. Take up neurotransmitters 5. Form glial scars (gliosis)  Oligodendrocytes - Present in white and gray matter - Interfascicular oligodendrocytes are located in the white matter of the CNS, where they produce the myelin sheath.  Ependymal cells. Line ventricles Microglia

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 Not a true neuroglial cell; derived from mesoderm whereas neuroglial cells, as well as neurons, are derived from ectoderm  Highly phagocytic cells ➢ Supporting cells of the PNS. Schwann cells  Satellite Schwann cells surround cell bodies in ganglia  Ensheathing Schwann cells - Surround unmyelinated axons. Numerous axons indent the Schwann cell cytoplasm and are ensheathed only by a single wrapping of plasma membrane. - Produce the myelin sheath around axons

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Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 19 NERVOUS TISSUE. NERVOUS FIBRES. NERVOUS ENDINGS Course 1

Faculty Medical The contents of the topic: MYELIN SHEATH ➢ The myelin sheath is formed by the plasma membrane of supporting cells wrapping around the axon. The sheath consists of multilamellar, lipid-rich segments produced by Schwann cells in the PNS and oligodendrocytes in the CNS.

➢ Functions  Increases speed of conduction (saltatory conduction)  Insulates the axon ➢Similar structure in CNS and PNS with some differences in protein composition

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➢Organization  Internode. Single myelin segment  Paranode. Ends of each internode where they attach to the axon  Node of Ranvier. Specialized region of the axon between myelin internodes where depolarization occurs ➢In the PNS, each Schwann cell associates with only one axon and forms a single internode of myelin. ➢In the CNS, each oligodendrocyte associates with many (40–50) axons (i.e. each oligodendrocyte forms multiple internodes on different axons). CONNECTIVE TISSUE INVESTMENTS OF NERVOUS TISSUE ➢Peripheral nervous system  Endoneurium. Delicate connective tissue surrounding Schwann cells; includes the basal lamina secreted by Schwann cells as well as reticular fibers  Perineurium. Dense tissue surrounding groups of axons and their surrounding Schwann cells, forming fascicles; forms the bloodnerve barrier  Epineurium. Dense connective tissue surrounding fascicles and the entire nerve ➢Central nervous system

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Meninges 1.1.Pia mater  Thin membrane lying directly on the surface of the brain and spinal cord  Accompanies larger blood vessels into the brain and spinal  cord 1.2.Arachnoid membrane  Separated from pia mater by connective tissue trabeculae Encloses the subarachnoid space, which contains blood vessels and the cerebrospinal fluid (CSF) produced by the cells of the choroid plexus  Together with pia mater, constitute the leptomeninges; inflammation of these membranes produces meningitis 1.3.Dura mater  Outermost of the meninges  Dense connective tissue that includes the periosteum of the skull THE REFLEX ARC ➢ The reflex arc is the simplest neuronal circuit and includes each of the elements discussed above. These circuits provide rapid, stereotyped reactions to help maintain homeostasis. To begin the reflex, a pseudounipolar, sensory neuron is activated by a receptor. The axon carries an afferent signal from the skin into the spinal cord where it synapses on a multipolar association neuron or interneuron. The interneuron signals a multipolar, motor neuron whose axon then carries an efferent signal to skeletal muscle to initiate contraction.

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SYNAPSE ➢ The function of the synapse is to alter the membrane potential of the postsynaptic target cell to either facilitate or inhibit the likelihood of the stimulus to be propagated by the postsynaptic cell. Most neurons receive thousands of synaptic contacts, both stimulatory and inhibitory, and the algebraic sum of these inputs determines whether the postsynaptic cell will depolarize. ➢ Classified according to postsynaptic target  Axodendritic. Most common  Axosomatic  Axoaxonic. Mostly occur at presynaptic terminals  Neuromuscular junction ➢ Structure of the synapse  Presynaptic component  Distal end of the axon branches, each branch terminating in a swelling or button called the terminal bouton.  Bouton contains synaptic vesicles/granules, which contain neurotransmitters and numerous mitochondria.  Synaptic gap/cleft. Separation (20–30nm) between pre- and postsynaptic cells.  Postsynaptic component - Formed by the membrane of the postsynaptic neuron or muscle cell and contains receptors for neurotransmitters - Membrane shows a postsynaptic density or thickening on its cytoplasmic side.

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 Bouton en passant. “Bouton-like” swellings along the length of an axon, allows a single axon to contact many distant cells. Common in smooth muscle innervation. AFFERENT TERMINATIONS OR SENSORY RECEPTORS Exteroceptive Receptors Free Nerve Ending  When the terminals of sensory nerves do not show any particular specialization of structure they are called free nerve endings. Such endings are widely distributed in the body. Free nerve endings are particularly numerous in relation to hair follicles. They respond mainly to deformation of hair i.e., they are mechanoreceptors. The abundance of free nerve endings in relation to hair follicles is to be correlated with the fact that hair increases the sensitivity of skin to touch. Free nerve endffigs may also be thermoreceplors and nociceptors. Tactile Corpuscles (of Meissner)  These are small oval or cylindrical structures seen in relation to dermal papillae in the hand and foot, and in some other situations. These corpuscles are believed to be responsible for touch. They are slow adapting mechanoreceptors.  It consists of an outer capsule and a central core. The capsule is made up of several layers of greatly folded cells and is continuous with the perineurium of nerves supplying the corpuscle. The core contains cells and nerve fibres. Each corpuscle is supplied by several myelinated nerve fibres. Some unmyelinated fibres may also be present. Lamellated Corpuscles (of Pacini)  These are much larger than tactile corpuscles. They may be up to 2mm in

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length. They are found in the subcutaneous tissue of the palm and sole, in the digits, and in various other situations. Lamellated corpuscles are believed to be fast adapting mechanoreceptors especially sensitive to vibration. They also respond to pressure.  Each corpuscle has a capsule, an intermediate zone, and a central core. The capsule is arranged in about thirty concentric layers (like the layers of an onion). The intermediate zone is cellular. The core consists of an outer layer of cells from which cytoplasmic lamellae project inwards and interdigitate with each other. In the centre of the core there is generally a single nerve fibre. The terminal part of the fibre is expanded into a bulb.

Bulbous Corpuscles (of Krause)  These are spherical structures about 50μm in diameter. They consist of a capsule within which a nerve fibre terminates in a club-shaped manner. Their significance is controversial. Some authorities regard them to be degenerating or regenerating terminals of nerve fibres rather than as specialized endings. Tactile Menisci (Merkel cell endings)  These are small disc-like structures seen in relation to specialized epithelial cells (Merkel cells) present in the stratum spinosum of the epidermis. The discs are expanded ends of nerve fibres. Merkel cells bear spine-like protrusions that interdigitate with surrounding epidermal cells. Tactile menisci are slow adapting mechanoreceptors sensitive to pressure. Ruffini endings  These are spindle-shaped structures present in the der-mis of hairy skin. Within a fibrocellular sheath there are collagen fibres amongst which there are numerous unmyelinated endings of myelinated nerve fibres. Ruffini endings are slow adapting cutaneous mechanoreceptoft responsive to stresses in dermal collagen. They resemble the Goigi tendon organs

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described below. DEGENERATION AND REGENERATION OF NEURONS When the axon of a neuron is cut across a series of degenerative changes are seen in the axon distal to the injury, in the axon proximal to the injury, and in the cell body. The changes in the part of the axon distal to the injury are referred to as unterograde degeneration or Wallerian degeneration. They take place in the entire length of this part of the axon. The neurofibrils within it break down into granules. The myelin sheath breaks up into small segments. It also undergoes chemical changes that enable degenerating myelin to be stained selectively. The Schwann cells increase in size and multiply in number. They act as macrophages and remove remnants of the axon and of myelin. At the same time the Schwann cells produce a large series of membranes that help to form numerous tubes. We shall see later that these tubes play a vital role in regeneration of nerve fibres. Degenerative changes in the neuron proximal to the injury are referred to as retrograde degeneration. These changes take place in the cell body and in the axon proximal to injury. The cell body of the injured neuron undergoes a series of changes that constitute the phenomenon of chromatolysis. The cell body enlarges tending to become spherical. The nucleus moves from the centre to the periphery. The Nissl substance becomes much less prominent and appears to dissolve away — hence the term chromatolysis. Ullrastructural and histochemical alterations occur in the cell body. The severity of the reaction shown by the cell body is variable. In some cases chromatolysis ends in cell death, followed by degeneration of all its processes. The reaction is more severe when the injury to the axon is near the cell body. If the cell survives, the changes described above are reversed after a period of time. It is sometimes observed that changes resulting from axonal injury are not confined to the injured neuron, bat extend to other neurons with which the injured neuron synapses. This phenomenon is referred to as transneuronal degeneration. Changes in the proximal part of the axon are confined to a short segment near the site of injury. If the injury is sharp and clean the effects extend only up to one or two nodes of Ranvier proximal to the injury. If the injury is severe a longer segment of the axon may be affected. The changes in the affected part are exactly the same as described for the distal part of the axon. They are soon followed by active growth at the tip of the surviving part of the axon. This causes the terminal part of the axon to swell up. It then gives off a number of fine branches. These branches grow into the connective tissue at the site of injury in an effort to reach the distal cut end of the nerve. We have seen that the Schwann cells of the distal part of the nerve proliferate to form a series of tubes. When one of the regenerating axonal branches succeeds in reaching such tube, it enters it and then grows rapidly within it. The tube serves as a guide to the growing fibre. Axonal branches that fail to reach one of the tubes degenerate. It often happens that more than one axonal branch enters the same tube. In that case the largest branch survives and the others

126 degenerate. The axon terminal growing through the Schwann cell tube ultimately reaches, and establishes contact with, an appropriate periphery end organ. Failure to do so results in degeneration of the newly formed axon. The new axon formed in this way is at first very thin and devoid of a myelin sheath. However, there is progressivij increase in its thickness and a myelin sheath formed around it. From the above account it will be clear that chanj ces of regeneration of a cut nerve are considerably increased if the two cut ends are near each other and if scar tissue does not intervene between them.

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Subject Histology, cytology and embryology Modul №1 Cytology, embryology and basic histology Submodul №2 Basic histology Topic 20 CONTROL TEST#2 Course 1

Faculty Dental

Self-control material: A. Questions to be answered: 1. Give the characteristic of the epithelium tissues? 2. What are the morphological varieties of epithelia? 3. Describe the structure of the simple epithelia? 4. Describe the structure of the stratified epithelia? 5. What cell’s attachments are there in the epithelia? 6. What are the functions of epithelial tissue? 7. What are the special elements in epithelia? 8. What are the glands? 9. What varieties of glands do you know? 10. Characterize structure of the exocrine gland? 11. Characterize varieties of the secretion? 12. What are the functions of the myoepithelial cells? 13. What is the connective tissue? 14. What cells of connective tissues do you know? 15. What are the main cells of connective tissue? 16. What are special cells in connective tissues? 17. What blood cells are there in connective tissues? 18. Characterize fibres of connective tissues? 19. Describe ground substance of connective tissues. 20. What are the functions of connective tissues? 21. What types of connective tissues do you know? 22. Characterize the areolar tissue? 23. Characterize the adipose tissue? 24. Characterize the reticular tissue? 25. Characterize the fibrous (collagenous) tissue? 26. Characterized mucous (primitive) connective tissue? 27. What is the cartilage? 28. What cells of cartilage do you know? 29. Characterize ground substance of cartilage? 30. What do you know about hyaline cartilage? 31. What do you know about elastic cartilage? 32. What do you know about fibrocartilage? 33. Where are the three cartilage tissues situated? 34. From what embryonic tissue derived cartilage? 128

35. Give the characteristics of growth and regeneration of cartilage? 36. Describe of structure of the bone tissue? 37. Give the classifications of bone? 38. What is the Haversian bone? 39. What is the mature human bone? 40. What bone cells do you know? 41. Describe the structure of the osteon? 42. Characterize the trabecular bone? 43. Characterize the bone formation? 44. What is the intramembranous ossification? 45. What is the endochondral ossification? 46. What are the stages of bone reparation? 47. Give characteristics of the blood? 48. What microscopic techniques use for investigate to blood? 49. Describe a structure of erythrocytes? 50. Give classification of leucocytes? 51. Describe the structure of neutrophil? 52. Describe the structure of eosinophil? 53. Describe the structure of basophil? 54. Describe the structure of lymphocyte? 55. Describe the structure of monocyte? 56. Describe the structure of platelets? 57. What are the muscle tissues? 58. Give the characteristics of skeletal muscle? 59. Describe the electron microscopy of sarcomer? 60. What are the red and white muscles? 61. Characterize the innervation of skeletal muscle? 62. Give the characteristic of cardiac muscle? 63. What are the similarities between cardiac and skeletal muscle? 64. Give the characteristic of smooth muscle? 65. Characterize the innervation of smooth muscle? 66. Characterize of ultrastructure of smooth myocyte? 67. What are the other contractile cells? 68. What is the nervous tissue? 69. What elements of nervous tissue do you know? 70. What are the neurons? 71. Describe the nerve cell structure? 72. What neuron staining use in histology? 73. What lineages of the nervous system do you know? 74. Is there variability in neuron structure? 75. What are the glial cells? 76. Describe the glial cell types? 77. What are the glial cells functions? 78. What are nervous fibres?

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79. Describe a myelination process? 80. Give the characteristics of synapses? 81. What are the degeneration and regeneration of neurons? 82. Give the characteristics of peripheral nerve endings? 83. Describe a structure of afferent termination? 84. Describe a structure of exteroceptive receptors? 85. Describe a structure of free nerve ending? 86. Describe a structure of proprioceptive receptors?

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“Cytology, Embriology and Basic histology” 1. Which of the following statements concerning the plasmalemma is CORRECT? A. Integral proteins are located only on the cytosolic side of the lipid bilayer B. Phospholipids are identical in composition in both the outer and inner regions of the lipid bilayer C. Sphingomyelin and ethanolamine are evenly distributed throughout the lipid bilayer D. Phospholipids having saturated and unsaturated fatty acids contribute to lipid asymmetry E. Pheripheral proteins are only found on the cytosolic side of the lipid bilayer 2.Which of the following statements relating to receptor sites of the plasmalemma is CORRECT? A. ACTH (adrenocorticotropic hormone) binds to receptor sites on the thyroid gland B. TSH binds to the phospholipids of the lipid bilayer C. The carbohydrate portion of membrane proteins act as receptor sites for ligands or hormones D. TSH (thyroid stimulating hormone) binds to receptor sites on the adrenal gland E. The receptor sites for ligands are located on the cytosolic side of the plasmalemа 3. Which of the following statements concerning phospholipids of the plasma membrane is CORRECT? A. The hydrophilic ends of phospholipids are permeable to ions such as Na+ B. The greater the number of double bonds on the fatty acid molecule of a phospholipid the more fluid is the membrane C. The hydrophilic ends of phospholipids are located in the central region of the lipid bilayer D. Saturated fatty acids of phospholipids contribute to membrane fluidity E. The hydrophilic ends of phospholipids interact with hydrophobic amino acids of integral proteins 4. Which of the following statements regarding the synthesis of protein on the RER (rough endoplasmic reticulum) is NOT CORRECT? A. A signal recognition particle binds to the signal peptide and stops further polypeptide elongation B. Proteins that are segregated in the RER contain an additional sequence of bases at the 5’ end C. First, a signal sequence of proteins is produce from translation of the mRNA D. The ribosome that translates the m RNA to produce the signal sequence is already attached to the endoplasmic reticulum E. The signal recognition particle-ribosomal complex then migrates and binds to a docking protein on the endoplasmic reticulum 5. Which of the following statements concerning the smooth endoplasmic reticulum is CORRECT? A. Stains with basic dyes B. Is involved in the synthesis of phospholipids for membrane formation C. Is not involved in glycogen metabolism D. It is abundant in cells that are producing proteins for export E. Initial glycosylation of proteins occurs here 6. Which of the following statements concerning the Golgi Complex is CORRECT? A. The phosphotransferase enzymes that produce the mannose 6phosphate residues are located in the trans Golgi network B. Receptor molecules for mannose-6-phosphate are present in the RER C. Synthesis of phospholipids occur in the cis Golgi network D. Phosphorylation of oligosaccharides that are attached to proteins to produce enzymatic proteins such as mannose-6phosphate residues occurs in the cis Golgi network E. Enzymes phosphorytated at the mannose 6-position all migrate to the zymogen granules 131

7. Which of the following components of the cell enhances acidophilia? A. Smooth endoplasmic reticulum B. Plasma membrane C. Rough endoplasmic reticulum D. Golgi complex E. Ribosomes 8. The primary function of intermediate filaments is to A. generate movement B. produce the structural core of microvilli C. provide mechanical stability D. produce the axoneme of flagella E. be involved in the movement of chromosomes 9. Which of the following processes concerning receptor mediated endocytosis is NOT CORRECT? A. Clathrin molecules separate from the coated vesicles and migrate back to the plasma membrane B. H+(ions) pumps neutralize the interior of the fuse endosome and coated vesicle C. A ligand binds to receptors on the outside of the plasma membrane D. Clathrin polypeptides are located on the cytosolic side of the invaginating coated pit E. The released receptors may return to the cell membrane to be reused 10. Which of the following structures are involved in the catabolism of hydrogen peroxide (H202) A. Smooth endoplasmic reticulum B. Lysosomes C. Peroxisomes D. Golgi complex E. Mitochondria 11. Which of the following is found primarily in the lamina densa of the basement membrane? A. Type III collagen and proteoglycans B. Type IV collagen and proteoglycans C. Microfibrils and proteoglycans D. Laminin and Fibronectin E. Reticular fibers and type VII collagen 12. Which of the following statements BEST describes immotile cilia (Kartagener's) syndrome? A. Degeneration of actin microfilaments B. Lack of dynein arms C. Lack of centrioles D. Absence of microtubules E. Lack of nexin proteins 13. Which of the following statements BEST describes pseudostratified columnar epithelium?All cells make contact with the basal lamina Nuclei are all located at the basal end of each cell Cells are all the same size and columnar in shape Columnar cells form the basal layer of cells and the intermediate layers above are composed of polyhedral cells Basal infoldings are a prominent feature of this epithelium 14. Which of the following surface specializations is unique to the cells lining the epididymis? A. Flagella 132

B. Cilia C. Stereocilia D. Microvilli and basal infoldings E. Cilia and microvilli 15. On the basal side of the cell, the cystoskeleton of the cell attaches the plasma membrane to the basal lamina via? A. Cytokeratin filaments B. Integrins C. Actin microfilaments D. Cadherins - Ca++ dependent proteins E. Proteoglycans 16. Which of the following statements concerning zonula adherens is CORRECT? A. Cadherins - Ca++ dependent proteins on the plasma membrane bind to actin microfilaments via vinculin and alpha-actinin B. Tonofilaments insert on cytosolic side of the plasma membrane of each cell C. An intermediate dense line of desmoglein is present in the intercellular space D. The intercellular space is 30 nm or greater E. The terminal web is composed only of actin microfilaments 17. Which of the following statements concerning meiosis is CORRECT? A. Separation of chromatids occurs during anaphase I of meiosis I B. Pairing of homologous chromosomes occurs in prophase I of meiosis I C. Non disjunction can only occur in meiosis II D. Crossing over of genetic material occurs in metaphase I of meiosis I E. Pairing of homologous chromosomes occurs in metaphase I of meiosis I 18. Which of the following statements concerning gametogenesis is CORRECT? A. Primary oocytes are arrested in the diplotene stage of prophase II before birth B. Primary follicles are all formed at the time of birth C. Primary spermatocytes are formed before birth D. Follicular cells of the primordial follicles secrete oocyte maturation inhibitor E. Ova are produced at the time of birth 19. During the process of fertilization: A. Acrosin and neuraminidase are released from the cortical granules. These enzymes digest the zona pellucida B. The sperm's plasma membrane fuses with the cells of the corona radiata C. The tail of the sperm drops off as the sperm touches the zona pellucida D. Acrosin and neuraminidase are released from the acrosome. These enzymes digest the zona pellucida E. The cortical granules release enzymes that digest the corona radiata cells 20. Which of the following statements concerning the fertilization process is CORRECT? A. Uncapacitated sperms can penetrate the secondary oocyte B. Enzymes released from the cortical granules cause the oocyte plasma membrane and the zona pellucida to undergo a conformational change C. The zygote that is produced has 1n chromosome number D. Several sperms normally penetrate the secondary oocyte E. Sperms become capacitated in the epididymis 21.Which of the following cell types are MOST COMMON in sensory ganglia? A. Pseudounipolar B. Golgi type I C. Multipolar D. Bipolar E. Golgi type H 22.Which of the following can NEVER be found in the initial segment? 133

A. Smooth endoplasmic reticulum B. Ribosomes C. Neurofilaments D. Neurotubules E. Axolemma 23. Which of the following statements concerning development of the zygote is CORRECT? A. The inner cell mass attaches to the endometrial layer B. The zygote undergoes several meiotic divisions to form the morula C. The blastocyst is composed of a compacted mass of cells D. The morula implants into the endometrial layer of the uterus E. At around 5-6 days, the blastocyst loses its zona pellucida and implants on the endometrium as a result of the trophoblast layer 24. During the 2nd week of development A. the uteroplacental circulation develops within the secondary yolk sac B. the primitive uteroplacental circulation is established as a result of the activity of syncytiotrophoblast cells on maternal sinusoids C. the inner cell mass is composed of trophoblast and hypoblast D. the bilaminar germ disc is composed of epiblast and trophoblast E. the amniotic cavity lies below the hypoblast layer of cells 25. Which of the following statements concerning embryonic development is CORRECT? A. Placenta praevia refers to implantation of the fertilized egg in the fallopian tube B. The trophoblast cells differentiates into syncytiotrophoblast and cytotrophoblast C. The germ disc during the second week of development is composed of epiblast, trophoblast and mesoderm D. The amnion develops around the 13th day of development and is called the secondary yolk sac E. The prochordal plate develops from the epiblast layer which is columnar in shape 27.Which of the following is NOT present in smooth muscle? A. Dense bodies B. Troponin C. Tropomyosin D. Calmodulin E. Myosin light chain Kinase 28. The MOST recognizable cell in the myeloid series is A neutrophil metamyelocyte B promyelocyte C. myeloblast D polymorphonuclear neutrophil E. neutrophil band 29. The transverse T-tubule of muscle cells A. depolarizes during muscle relaxation B. transmits an electrical signal from the sarcolemma to the sarcoplasmic reticulum C. is present in smooth muscle tissue D. is part of the smooth endoplasmic reticulum E. encircles the H-band 30.What are Nissl bodies? A. Rough endoplasmic reticulum B. Bundles of neurotubules C. Golgi apparati D. Arrays of mitochondria E. Synaptic vesicles 134

31. Which of the following statements concerning red blood cell is CORRECT? A. Cells possess lots of mitochondria and rough endoplasmic reticulum B. They possess a round nuclei with two or more nucleoli C. A drumstick is attached to the nucleus D. Cells are biconcave and lack nuclei E. They are derived solely from the spleen 32.The sarcoplasmic reticulum of a skeletal muscle is A. a type of rough endoplasmic reticulum B. a site of glycogen storage C. a site into which calcium is released during muscle relaxation D. a site of calcium - binding protein (calsequestrian) and a Ca++ - activated ATP pump E. not found surrounding myofibrils 33.Which of the following statements is CORRECT regarding cardiac muscle? A Gap junctions are absent B Triads are present at the A-I junction C Intercalated discs contain zonulae occludentes D Is capable of extensive regeneration E. Cells are long and possess many nuclei located under the sarcolemma 34. Which of the following cell types differentiates into macrophages? A. Neutrophil B. Fibroblast C. Chondroblast cell D. Plasma cell E. Monocyte 35. Which of the following statements concerning loose areolar connective tissue is NOT CORRECT? A. It is composed of a dense arrangement of collagen fibers B. It has lots of ground substance C. It is composed of a great abundance of different cell types D. It is found around glandular units E. It is found surrounding small blood vessels 36. In the biosynthesis of collagen A. the signal peptides of the procollagen molecule is removed in the Golgi complex specific proteases (procollagen peptidase) remove the registration peptides within the cytosol

C. procollagen molecules are soluble due to the registration peptides D. glycosylation of specific proline occurs before hydroxylation E. polypeptide alpha chains are formed on SER 37. In certain pathological conditions, the amount of tissue fluid may increase thus causing edema. This condition may be BEST characterized by A. lack of plasma proteins due to protein deficiency B. lack of proteoglycans C. deficiency of glycosaminoglycans D. over production of collagen fibers E. constriction of the arterioles 38. Which of the following statements regarding proteoglycans in ground substance is CORRECT? The glycosaminoglycans of proteoglycans have a high negative charge that attracts cations (such as Na+) and binds to water molecules B. The glycosaminoglycans make up about 20% of the proteoglycan molecule 135

C. The glycosaminoglycans are called perlacans D. Proteoglycans contain branched chain polysaccharides E. Hyaluronic acid is a typical proteoglycan molecule that binds to heparan sulfate and chondroitin sulfate 39. Which of the following statements regarding an allergic reaction to bee venom is CORRECT? A. A second exposure to the same venom causes the antigen to first bind to macrophage B. Macrophages release histamine, heparin and leukotrienes C. The antigen (bee venom) first binds to the IgM of mast cells D. IgE production from plasma cells binds to the plasma membrane of mast cells E. During the 2nd exposure to the antigen, mast cells are converted to macrophages 40. In which part of collagen biosynthesis does vitamin C influence? A. Packaging of procollagen in the Golgi complex B. Formation of polypeptides in the RER C. Glycosylation of specific hydroxylysine residues in the RER D. Removal of registration peptides E.Hydroxylation of specific proline and lysine residues in the RER 41. Which of the following statements concerning the plasma membrane is INCORRECT? A. The phospholipids are amphipathic molecules B. The proteins can only be associated with the membrane as peripheral proteins C. The membrane exists as a bilayer structure, with phospholipids on both the interior and exterior surfaces D. It is composed of phospholipids and proteins E. Fluidity of the membrane is controlled by the combination of unsaturated fatty acids in the phospholipids and cholesterol molecules in the membrane 42. Which one of the following statements concerning the eukaryotic cell is INCORRECT? A. While certain types of cells possess their own unique forms of intermediate filament proteins, they all possess lamins A, B, and C “Dynamic instability” is a property of microtubules Lacking a nucleus, eukaryotic cells have their DNA scattered throughout the cell D. Thin filaments are used by the cell for locomotion E. Electron microscopists distinguish smooth endoplasmic reticulum from rough endoplasmic reticulum by the presence of ribosomes 43. Which of the following statements concerning the nuclear structure is INCORRECT? The nucleolus is composed of three parts: a granular component, a fibrous component, and a limiting membrane Lying adjacent to transcriptionally inactive heterochromatin, perichromatin granules may be the sites of gene transcription The fibrous lamina is composed of intermediate filament proteins The double membranes of the nuclear envelope are continuous with the rough endoplasmic reticulum E. Each nucleus of every human cell contains the same DNA 44. Which of the following statements is INCORRECT? Two copies of histones Hl, H2A, H2B, and H3 make up the core of the histone complex, while histone H4 lies in the linker region The nucleosome coils themselves are then coiled into a structure called the solenoid All of this coiling of the DNA serves three functions: to reduce the overall length of the DNA to a size that will fit the nucleus, to protect the DNA from shearing, and to store unused DNA Nucleosomes are composed of proteins, around which are wound the cellular DNA The nucleosomal structure can be made even more compact by phosphorylation of 136

the histones 45. Which of these distinguishing features of the stages of mitosis is INCORRECT? A. Anaphase - separation of the chromatids from chromosomes B. Prophase - duplication of the centrioles C. Prometaphase - breakdown of the nuclear envelope D. Telophase - reformation of the nuclear envelope E. Metaphase - alignment of the chromosomes 46. Which of the following statements is INCORRECT? A. Taxol inhibits the removal of tubulin dimers from microtubules B. Dynein motors move toward the minus end of microtubules C. Spindle fibers run between the centrioles of a mitotic cell D. Kinesin-like motors act to push adjacent spindle fibers apart E. The kinetochore is involved in the addition of tubulin dimers during anaphase 47. One of the following functions DOES NOT involve proteins of the hsp70 family: A. Degradation of misfolded proteins B. Import of mitochondrial proteins C. Folding of cytosolic proteins D. Import of endoplasmic reticulum proteins E. Folding of mitochondrial proteins 48. Which one of the following events during the synthesis and export of proteins DOES NOT take place before a protein leaves the rough endoplasmic reticulum? A. Addition of mannose-6-phosphate to proteins destined for the lysosome takes place B. Protein folding by calnexin and BiP takes place C. A signal recognition particle (SRP) binds to the signal peptide and the ribosomes D. The ribosome receptor and the SRP receptor bind the ribosomes to the endoplasmic reticulum E. SRP leaves the ribosome and the signal peptide, allowing translation to continue 49.Where in the neuron is the action potential generated? A. Postsynaptic membrane B. Axon Hillock C. Initial segment of the axon D. First internodal segment of axon E. Dendritic membrane 50. In long bone development, the ossification zone has A. woven (immature) bone deposited on the hypertrophied chondrocytes B. woven bone deposited on the calcified cartilage C. lamella bone deposited on the calcified cartilage D. lamella (mature) bone deposited on the hypertrophied chondrocytes E. the presence of chondroblast cells 51.Cells having basal infoldings are characteristic of A. ion transport B. mucus secretion at the apical end of the cell C. cells having lots of desmosomes D. cells lacking mitochondria on the basal side E. cells lacking endoplasmic reticulum on the basal side 52. Microvilli are structures that A. have a core of actin microfilaments B. are involved in the movement of materials over the cell surface C. have a core of microtubules D. are involved in cellular movement E. utilize the sliding filament mechanism for movement 137

53.Which of the following features is NOT a characteristic of epithelia? A.Epithelia display lateral communications B.Epithelia display avascularity C.Epithelia display polarity D. Epithelia are normally separated by large (2 microns) intercellular spaces E.A basal lamina is produced by the basal cells of epithelia 54. Which of the following statements regarding loose areolar connective tissue is CORRECT? A. Avascularity is a typical feature of the tissue B. Has lots of ground substance C. Has few cells within the tissue D. Ground substance is scant E. Is found in areas that can withstand considerable stress 55. Which of the following statements regarding proteoglycans in connective tissue is CORRECT? A. Contain glycosaminoglycans that possess a high negative charge due to the sulfate and carboxyl groups B. Are not capable of attracting large amounts of water molecules C. The proteins of proteoglycans are the predominant fraction of the proteoglycan molecules D. Are composed of a core protein and a branched carbohydrate residue E. Lack binding sites for collagen type II 56. Which of the following cell types is generally regarded as the principal cell type of connective tissue? A. Plasma cell B. Mast cell C. Adipocytes D. Fibroblast E. Osteoclast cell 57. Which of the following statements regarding collagen biosynthesis is CORRECT? A. Hydroxylation of proline residues occurs in the Golgi Apparatus B. The procollagen molecule becomes insoluble within the cytoplasm C. Glycosylation of specific hydroxy lysines occur in the clathrin vesicles that are migrating to the plasma membrane D. Specific (procollagen) proteases remove registration peptides outside the cell membrane E. Only actin microfilaments are involved in the movement of secretory vesicles 58. Which of the following statements regarding hyaline cartilage is CORRECT? A. Nerves penetrate the cartilage matrix B. Chondrocytes are mature cells that are unable to undergo mitosis C. Articular cartilage is covered by a perichondrium D. Collagen type II is the predominant fiber of perichondrium E. The chondrocyte is surrounded by a territorial matrix that is rich in glycosaminogycans 59. Which of the following cell types is involved primarily in the synthesis of collagen type 1? A. Chondrocytes B. Osteoclast cells C. Macrophages D. Osteoblasts E. Chondroblasts 60. Which of the following statements regarding bone is NOT CORRECT? A. The mineral component of bone is composed primarily of calcium phosphate B. Growth in length of long bone is an example of endochondral ossification C. Osteoblast cells produce the osteoid matrix vesicles of bone D. The eosinophilia of bone matrix is caused by the high concentration of 138

collagen type 1 E. Osteocytes are located on the surface of the bone 61. Which of the following statements regarding endochondral ossification is NOT CORRECT? A. The calcification zone of cartilage is composed of dead chondrocytes surrounded by cartilage matrix B. The calcified cartilage within the ossification zone is covered with new bone produced by osteoblast cells C. The epiphyseal plate towards the diaphysis is replaced by new bone formation D. Osteoclast cells destroy bone material intracellularly E. Increase in the length of bone is due to the presence of the epiphyseal plate 62. The thin myofilament of skeletal muscle fibers are anchored to the Z-line by: A. Desmoglein B. C-protein C. Myomesin D. Titin E. Alpha actinin 63. Which of the following statements regarding skeletal muscle is CORRECT? A. The T-tubules and terminal cisternae of SER are located at the Z-line B. The RER and T-tubules are located at A-I junction C. All mitochondria are located just beneath the sarcolemma D. Diads are located at the A-I junction of sarcomeres E. The T-tubule and terminal cisternae of SER and are located at the A-I junction 64. Cardiac muscle cells have A. SER which have dilated cisternae that are better developed than SER of skeletal muscles B. intercalated disc that bind cells together C. triads that are located at the A-I junction D. intermediate filaments that act as Z-line E. SER which sequester Ca++ from the sarcoplasm 65. The mast cell possesses receptor molecules on the surface of the cell for: A. IgE B. IgA molecules C. Lactoferrin D. IgM E. IgD 66. Which of the following statements concerning meiosis is CORRECT? A. Duplication of DNA occurs in prophase 1 of meiosis 1 B. The genetic material produced in each of the cells during meiosis are identical C. Pairing of homologous chromosomes occurs in prophase 1 of meiosis 1 D. Non disjunction does not occur in meiosis II E. Separation of chromatids occurs during anaphase 1 of meiosis 1 67. Which of the following statements concerning gametogenesis is CORRECT? A. Primary oocytes are all arrested in the diplotene stage of prophase 1 before birth B. All primary oocytes are formed after puberty C. All primary spermatocytes are formed at the time of puberty D. All primary spermatocytes are formed before birth E. The transformation from spermatogonia to spermatozoa takes about 16 days 68.Considering the normal course of events in epidermal cell formation, the last keratinocytes to have all functional organelles are the: A. Horny cells B. Basal cells C. Granulosum cells 139

D. Lucidum cells E. Spinosum cells 69.Which the following glial cells contribute to the formation of Cerebro-Spinal fluid (CSF)? A. Microglial cells B. Ependymal cells C. Astrocytes D. Oligodendrocytes E. Macroglial cells 70. During the process of fertilization A. the theca interna cells release estrogen as a result of contact with the sperm B. enzymes released from cortical granules cause a conformational change of the zona pellucida and oocyte plasma membrane C. the sperm's plasma membrane fuses with the cells of the corona radiata D. the sperm first penetrates the basal lamina E. after the sperm makes contact with the zona pellucida, more sperms are allowed to penetrate the developing oocyte 71. During the second week of development A. the inner cell mass is composed of three germ layers B. blood vessels develop in the allantoic sac the uteroplacental circulation developes within the yolk sac syncytiotrophoblast erodes the lining of the maternal blood vessels to establish the primitive uteroplacental circulation E. the cytotrophoblast erodes the maternal blood vessels of the endometrium 72. Which of the following statements is CORRECT during the first two weeks of development? A. The zygote undergoes several meiotic divisions B. The morula with its corona radiata implants into the endometrium C. The inner cell mass gives rise to the syncytiotrophoblast and cytotrophoblast D. The trophoblast gives rise to the epiblast and hypoblast layer E. The prochordal plate develops from the hypoblast layer 73.The blood vessels of the umbilical cord are derived from: A. Yolk sac B. Developing heart C. Chorion D. Allantois E. Amnion 74. A one-week-old baby presents with secretions draining from the umbilicus. The MOST LIKELY diagnosis is: A. Meckel's diverticulum B. Omphalocele C. Intestinal stenosis D. Anular pancreas E. Gastroschisis 75. By the end of the third week, mesoderm formed from the epiblast by invagination at the primitive streak has been organized into three general regions, one of which will give rise to somites, and is called the: A. Intermediate mesoderm B. Extraembryonic somatic mesoderm C. Extraembryonic splanchnic mesoderm D. Lateral plate mesoderm E. Paraxial mesoderm 76. Which of the following structures is derived from ectoderm? 140

A. Liver B. Anterior pituitary gland C. Digestive tract D. Respiratory tract E. Allantois 77. The azurophilic granules found in neutrophils are: A. Histamine B. Pigment granules C. Lysosomes D. Mitochondria E. Rough endoplasmic reticulum 78. Which of the following is characteristic of red blood cells? A. They produce hemoglobin B. They stain basophilic because of large amounts of ribosomes C. They are produced in the adrenal D. They have bi-lobed nucleus E. They are produced in the bone marrow 79. Which of the following is INCORRECT regarding sickle cell disease? A. It results in the formation of abnormal reticulocytes B. The abnormal hemoglobin found is Hb C C. It has autosomal dominant inheritance D. It is an abnormality of eosinophils E. The defect is in the B chain of hemoglobin 80.Which of the following statements concerning the structure of the plasma membrane is CORRECT? A. The glycocalyx is present on the cytosolic side of the plasma membrane Carbohydrates are located within the lipid bilayer All integral proteins lack carbohydrate moieties on the external side of the plasma membrane Carbohydrates attached to some proteins and lipids form the glycocalyx on the external side of the plasmalemma Intermediate filaments attach to the carbohydrate portions of the glycoproteins 81. Which of the following statements concerning the plasmalemma is CORRECT? A. Phospholipids such as sphingomyelin and phosphatidy-choline are evenly distributed in the outer and inner half of the plasma membrane B. Phospholipids with unsaturated fatty acid tend to enhance fluidity of the membrane C. Phospholipids are only composed of saturated fatty acids D. Phospholipids are identical in composition in both the outer and inner regions of the lipid bilayer E. Pheripheral proteins are only found on the external side of the lipid bilayer 82.Which of the following statements relating to receptor sites of the plasmalemma is CORRECT? A. FSH (follicle stimulating hormone) binds to receptor sites on the thyroid gland B. The receptor sites for ligands or hormones are located on the cystosolic side of the plasmalemma C. ACTH (adrenocorticotropic hormone) binds to receptor sites on the thyroid gland D. The lipid bilayer of the phospholipids act as receptor molecules for ligands E. The receptor sites for ligands or hormones are due to the carbohydrate portions of membrane proteins on the external side of the plasmalemma 83. Which of the following structures is responsible for the lack of movement of cilia? A. Nexin proteins lacking the enzyme ATPase B. The microtubule of cilia lack the triplet formation C. Dynein arms lacking the enzyme ATPase 141

D. The axoneme of cilia lack the subfiber C E. The actin microfilaments of cilia lack the enzyme ATPase 84. Which of the following statements regarding the synthesis of proteins on the RER (rough endoplasmic reticulum) is CORRECT? A. Proteins destined for export on the plasma membrane are produced on cytosolic polyribosomes B. Proteins to be segregated in the lumen of RER lack a signal sequence of the protein molecule C. Before translating mRNA, all ribosomes are already attached to the endoplasmic reticulum D. The signal recognition particle (SRP) - ribosomal complex migrates and binds to a docking protein on the endoplasmic reticulum E. The signal recognition particle stays attached to the ribosomal complex in order to translate the complete mRNA. 85.Following injury to the central nervous system, the cells MOST responsible for "cleaning up debris " are: A. Microglia B. Neurons C. Astrocytes D. Ependymal Cells E. Oligodendroctyes 86. Which of the following statements concerning the smooth endoplasmic reticulum is CORRECT? A. It stains with basic dyes B. It is present in large quantities in cells that produces lots of proteinaceous materials C. Phenobarbital (a barbiturate) increases the amount of SER and enzymes in liver cells so that the drug can be detoxified D. Steroidal cells possess lots of RER and few SER E. Membrane formation does not take place on the SER 87. Which of the following statements regarding the organelles of a cell is CORRECT? A. Proteins for export are manufactured on the cytosolic ribosomes B. Lysosomal enzymes are derived from cytosolic ribosomes C. Glycolytic enzymes are made in the RER D. Peroxisomal enzymes are derived from cytosolic ribosomes E. Initial glycosylation of proteins for export occurs in the cis Golgi network 88. Microvilli are structures that A. are composed of intermediate filaments B. allow flagella of spermatozoa to move C. are made of microtubules that bind to the terminal web D. are made of actin microfilaments E. have basal bodies at their bases 89. Which of the following structures binds integral proteins to collagen type IV? A. Integrins B. Reticular fibrils (collagen type III) C. Anchoring fibrils (collagen type VII) D. Laminin E. Proteoglycans 90. Which of the following statements is CORRECT for epithelia? A. They are surrounded by lots of ground substance B. They are vascularized C. They demonstrate strong lateral adhesions such as macula adherens D. They lack the presence of basal lamina 142

E. Pseudostratified columnar epithelium of the trachea lack surface specialization 91. Which of the following statements concerning surface (covering) epithelia is CORRECT? A. Classification is based upon the nature of the duct system B. Classification can be based only on the number of cell layers C. Ciliated simple columnar epithelium can be classified base on number of cell layers, shape of the cells, and surface characteristics D. Pseudostratified columnar epithelium is composed of several layer of cells E. Classification can be determined on the mode of secretion 92.Where in the ventral horn cell (lower-motor neuron) is the action potential generated? Axon hillock Initial segment of the axon First internodal segment of the axon Postsynaptic membrane Dendritic membrane 93. Which of the following statements regarding collagen biosynthesis is CORRECT? A. Glycosylation of lysine occurs before the hydroxylation step B. The registration peptides are removed in the RER C. Procollagen peptidase acts on the tropocollagen molecule within the Golgi complex D. Hydroxylation of proline occurs in the RER E. The tropocollagen molecule is secreted as an insoluble molecule from the secretory vesicle 94. Which of the following statements regarding cells involved in an allergic reaction is CORRECT? A. Fibroblast cells secrete IgM antibodies Receptor molecules on the surface of mast cells first bind to the antigen (pollen or toxin material) Receptor molecules on the surface of mast cells first binds to IgE D. Mast cells secrete IgE antibodies E. Mast cells secrete IgA antibodies after being stimulated by an antigen 95.Which of the following cell types is involved in the production of the periodontal ligament? A. Cementoblasts B. Ameloblasts C. Fibroblasts D. Odontoblasts E. Osteoblasts 96.In contrast to the soma, axons DO NOT contain: A. Smooth endoplasmic reticulum B. Microtubules C. Mitochondria D. Neurofilaments E. Nissl bodies 97. Which of the following statements concerning gametogenesis is CORRECT? A. Primary spermatocytes are formed before birth B. The follicular cells of primordial follicles secrete oocyte maturation inhibitor (OMI) that stops the development of the primary oocyte C. Primary oocytes secrete the oocyte maturation inhibitor D. Before birth, the primary oocytes are all arrested in metaphase II E. Primary oocytes are all formed only at the time of puberty 98. Which of the following statements regarding the DNA content of cells is CORRECT? A. Spermatids have 2n DNA B. Secondary spermatocytes have 2n DNA C. Primary spermatocytes have 2n DNA and 46 pairs of chromosomes 143

D. Spermatozoa have 23 pairs of chromosomes E. Spermatogonia have 2n DNA and 46 pairs of chromosomes 99. Which of the following statements concerning sickle cell disease is CORRECT? A. The hemoglobin is exactly the same as in normal red blood cells B. The sickled erythrocyte is flexible and hence have a long life span C. Valine in the normal red blood cell is replaced by glutamic acid D. Erythrocytes from Hbs patients are inflexible, rigid and fragile E. Erythrocytes from Hbs patients are biconcave in shape 100. Which of the following statements concerning the fertilization process is CORRECT? A. The cortical granules release enzymes that alter the oocyte plasma membrane and the zone pellucida thus preventing polyspermy B. Acrosin and neuramiaidase are enzymes released by the cortical granules to alter the oocyte plasma membrane C. The sperm's plasma membrane fuses with the plasma membrane of the corona radiata cells D. A zonal reaction occurs after fusion of the male pronucleus to the female pronucleus E. The uncapacitated sperm are able to fertilize the egg 101. Cells are constantly bathed in tissue fluid which has passed through the capillary wall via hydrostatic pressure. The force associated with most of this fluid being drawn back into the venule is A. hydrostatic pressure B. venous pressure C. colloid osmotic pressure D. arterial pressure E. lymphatic pressur 102. Lysosomal activity is a common feature of long-lived cells such as neurons and cardiac muscle cells. The residual bodies frequently observable with the microscope in these cells are known as A. lipofuscin granules B. zymogen granules C. lipid droplets glycogen crystals 103.Which of the following cell types is primarily involved in the presentation of epitopes by means of class II major histocompatibility complexes? A. CD 4 T-lymphocytes B. CD 8 T-lymphocytes C. Macrophages D. Plasma cells E. Eosinophils 104.Which of the following cell types is primarily involved in the humoral immune response? A.Eosinophils B.Macrophages C. Plasma cells D. Neutrophils E. Killer T-cells 105.The MOST immature recognizable cell in the myeloid series is: A. Myelocyte B. Metamyelocyte C. Myeloblast D. Promyelocyte E. Band cell 144

106. During early embryonic development A. the zygote produces blastomeres as a result of meiotic division B. the inner cell mass develops into the cytotrophoblast layer C. the morula has a definitive blastocoel cavity D. the blastocyst has develop an inner cell mass and a trophoblast layer by day 5-6 E. the corona radiata cells are still present at the time of implantation 107. During the 2nd week of development A. the inner cell mass has differentiated into syncytiotrophoblast and cytotrophoblast B. the amniotic cavity is formed by day 14 C. cytotrophoblast cells erode the maternal sinusoids to establish the primitive uteroplacental circulation. D. the prochordal plate forms from the epiblast E. the germ disc is made up of an epiblast and hypoblast layer of cells 108. Which of the following statements is CORRECT during the 2nd week of development? A. Ectopic pregnancy refers to development of the embryo in the uterus during the 2nd week of development B. Placenta previa refers to development in the 2nd week within the oviduct C. The amnioblast cells of the amniotic sac is derived from the hypoblast layer D. The prochordal plate which forms at around day 14 of development is derived from the hypoblast layer E. The prochordal plate is tall columnar in shape and is derived from the epiblast layer 109.The stratum granulosum: A. Contains melanocytes B. Is seen only in thick skin C. Normally shows mitotic activity D. Is the last epidermal layer to have nuclei E. Is also known as the stratum corneum 110.An orthochromatic erythroblast: A. Displays both basophilic and eosinophilic cytoplasm B. Is intensely basophilic,, C. Has a nuclei which displays loose lacy chromatin D. Shows multiple nucleoli E. Extrudes its nucleus 111.The term "a shift to the left" refers to A. an increase in the population of band neutrophils in circulating blood B. a decrease in the population of red blood cells C. an increase in the population of reticulocytes D. an increase in the population of mature eosinophils in circulating blood E. a decrease in the population of polymorphonucleocytes. 112. Which of the following statements concerning cartilage is CORRECT? A. Hyaline cartilage is composed of proteoglycans, glycosaminoglycans and collagen type I B. Elastic cartilage has collagen type I and elastic fibers C. Chondrocytes produce and release collagen type I in the interterritorial matrix D. A perichondrium covers hyaline cartilage on the sides and on the articulating surfaces E. Hyaline cartilage is composed of collagen type II, chondronectin, proteoglycans and glycosaminoglycans 113. Which of the following statements concerning hyaline cartilage is CORRECT? A. The matrix is composed of hydroxy apatite crystals B. The articulating surface increases by means of interstitial growth C. Chondrocytes within the cartilage model divide and grow by appositional means D. The perichondrium is composed of loose connective tissue, primarily collagen type II

145

E. Isogenous groups are formed within the inner region of the perichondrium adjacent to cartilage 114. Osteoblast cells…. A. are derived from bone marrow cells B. are involved in the production of collagen type II and chondronectin C. secrete large amounts of acid phosphatase for bone degredation D. have a basophilic cytoplasm since they produce lots of protein aceous material E.form Howship's lacunae 115. Osteoclast cells……. A. are involved in the synthesis of collagen type I of bone B. are derived from osteoblast cells C. are influenced by calcitonin cells to increase resorption of bone , D. release their lysosomal enzymes outside the cell so that destruction of the bone can occur E. can be converted to osteocytes 116. Which of the following statements regarding compact bone is CORRECT? A. Collagen fibers are arranged randomly B. Osteons are composed of osteoclast cells C. Osteons are found in the outer circumferential lamellae D. Canaliculi enclose cytoplasmic extensions of osteocytes in osteons E. The ground substance is made up of chondronectin and proteoglycans 117. During the process of endochondral ossification A. the bone collar that forms early in development is derived from the epiphyseal plate B. the primary ossification center lies between the articulating cartilage and the epiphyseal plate C. the bone collar is produced by chondroblast cells D. the epiphyseal plate is responsible for increase in length of long bones E. the calcified cartilage of the epiphyseal plate has viable chondrocytes 118. Which of the following cell types is involved in the release of histamine? A. Plasma cell B. Macrophage C. Mast cells D. Fibroblast E. Mesenchymal cell 119. DNA is duplicated in the cell cycle during the: A. G2 phase. B. S phase. C. M phase. D. G1 phase. E. G0 phase. 120. Which one of the following statements concerning the plasma membrane is INCORRECT? A. The membrane is a bilayer structure, with phospholipids on both the interior and exterior surfaces B. Phospholipids are amphipathic molecules C. Biological membranes are composed of phospholipids and proteins D. Fluidity of the membrane is controlled by the combination of fatty acids in the phospholipids and cholesterol molecules in the membrane E. Proteins can only be associated with the membrane as peripheral proteins 121. Which one of the following statements concerning the eukaryotic cell is INCORRECT? A. Electron microscopists distinguish smooth endoplasmic reticulum from rough endoplasmic reticulum by the presence of ribosomes B. Eukaryotic cells have their heterochromatin scattered throughout the cell 146

C. While certain types of cells possess their own unique forms of intermediate filament proteins, they all possess lamins A, B, and C Thin filaments are composed of actin Microtubules possess functionally different ends, called positive and negative 123. Which one of the following statements concerning the nuclear structure is INCORRECT? A. The nucleolus is composed of three parts: a granular component, a fiberous component, and the nuclear envelope. B. The fiberous lamina is composed of intermediate filament proteins. C. Lying adjacent to transcriptionally inactive heterochromatin, perichromatin granules may be the sites of gene transcription. D. Each nucleus of every human somatic cell contains the same DNA. E. The double membranes of the nuclear envelope are continuous with the rough endoplasmic reticulum. 124. Which one of the following statements concerning the nuclear envelope is INCORRECT? A. It is continuous with the membranes of the rough endoplasmic reticulum. B. It serves as the boundary between the cytoplasmic and nuclear compartments. C. It contains pores that regulate passage of materials in both directions between nucleus and cytoplasm. D. It is the site of synthesis of proteins that form elements of the nuclear matrix. E. It is stabilized on its inner aspect by filaments of the nuclear lamina. 125. Which one of the following statements is INCORRECT? A. Nucleosomes are composed of proteins, around which are wound the cellular DNA. B. Two copies each of histones H2A, H2B, H3, and H4 make up the core of the histone complex, while histone Hl lies in the linker region. C. The nucleosomal structure can be made even more compact by phosphorylation of the nuclear lamins. D. All of the coiling of the DNA serves three functions: to reduce the overall length of the DNA to a size that will fit in the nucleus, to protect the DNA from shearing, and to store unused DNA. E. The nucleosome coils themselves are coiled into a structure called the solenoid.

126. A 35-year-old woman has had progressive pain and loss of vision in her right eye over the past 24 hours. Visual acuity is 20/100 in the right eye. Funduscopic examination of the right eye demonstrates a swollen optic disc. Visual evoked response testing demonstrates a markedly slowed nerve conduction velocity in the right optic nerve due to demyelination. Her condition is MOST LIKELY due to an immune attack on which of the following cells? A. Oligodendrocytes B. Astrocytes C. Microglia D. Neurons E. Schwann cells 127.Which of the following correlations is INCORRECT? A. Pre-otic somites to extraocular muscles B. Epimere to erector spinae muscles C. Cervical somites to abdominal muscles D. Occipital somites to tongue muscles E. Cervical somites to diaphragm 128.Which statement is CORRECT regarding melanocytes? A. They are also called melanophores B. They require the enzyme tyrosine to change DOPA to melanin C. They are found in the stratum granulosum D. They are derived from neural crest cells 147

E. Caucasians have a reduced number of melanocytes 129.Which of the following is a receptor for vibratory pressure? A. Merkel's Corpuscle B. Meissner's Corpuscle Ruffini Corpuscle Pacinian Corpuscle Free Nerve Endings 130.Which one of the following events during the synthesis and export of proteins DOES NOT take place before a protein leaves the rough endoplasmic reticulum? A. Protein folding assisted by calnexin and BiP takes place B. Sorting of secretory proteins C. The first sugars are added to form glycoproteins D. A signal recognition particle (SRP) binds to the signal peptide and the ribosome E. SRP leaves the ribosome and the signal peptide, allowing translation to continue 131.Which of the following is NOT surrounded by a sheath from a supporting cell? A. Peripheral myelinated axons B. Peripheral unmyelinated axons C. Central myelinated axons D. Central non myelinated axons E. Axons from motor neurons 132.A 25-year-old female is diagnosed with severe iron deficiency anemia. She has been started on appropriate therapy. A good indicator that she is responding well to treatment is the presence in the peripheral blood of: A. Abundant myeloblasts B. Neutrophils C. Reticulocytosis D. Abundant proerythroblasts E. Abundant promyelocytes 133.A 65-year-old woman with atrial fibrillation has a stroke of the left cerebral hemisphere due to occlusions of the left middle cerebral artery by an embolus. Over the next several months, scar tissues forms in the brain at the site of infarction. Which of the following cells is MOST LIKELY to have participated in forming this scar? A. Microglia B. Oligodendroglia C. Astrocytes D. Ependymal cells E. Satellite cells 134.Which of the following statements about epithelia is NOT TRUE? A. They are vascular. B. They are polarized. C. They are separated from the underlying connective tissue by a basal lamina. D. They contain only a small amount of intercellular substance. E. They line the lumen of blood vessels. 135.Which one of the following statements DOES NOT apply to the basal lamina? A. It contains Type IV collagen. B. It contains laminin and perlacan C. It consists of a lamina densa and a lamina lucida. D. It contains heparin sulfate. E. It contains the lamina reticularis, secreted by fibroblasts. 148

136.Which one of the following cellular junctions prevents the free diffusion of materials across the epithelial cell layer? A. Gap junction. B. Hemidesmosome. C. Adherence junction. D. Tight junction. E. Desmosome. 137.Which of the following statements about microvilli is NOT TRUE? A. They include stereocilia. B. They contain a core of keratin filaments. C. They facilitate absorption. D. They are approximately 1 micrometer in length, 1000/cell, and increase the surface of the apical membrane by 10-fold. E. They form the brush border in the proximal tubule of the kidney. 138.The beating of cilia and flagella is dependent upon which of the following processes? A. Polymerization and depolymerization of microtubules. B. Attachment of actin thin filaments to the membrane. C. Attachment and release of dynein side arms between adjacent microtubules of each doublet. D. Attachment and release of doublet microtubules from the central pair of singlet microtubules. E. Attachment and release of fimbrin and vilin. 139.Which one of the following statements about glands is TRUE? A. Exocrine glands lack ducts. B. Simple glands have ducts that branch. C. Endocrine glands secrete into ducts. D. Serous secretions are watery. E. Holocrine glands release their contents by exocytosis. 140.A patient visiting your fertility clinic is found to have immotile sperm cells. During the follow-up consultation you discover that he is subject to chronic respiratory tract infections. This patient is LIKELY to have abnormal: A. Gap junctions. B. Cilia. C. Microvilli. D. Desmosomes. E. Peroxisomes. 141.Which one of the following cell types produces collagen, proteoglycans and glycosaminoglycans? A. Plasma cells B. Mesenchymal cells C. Mast cells D. Fibroblasts E. Macrophages 142.Which of the following statements concerning immediate hypersensitivity reaction is CORRECT? A. The fibroblast cell secretes IgE, which binds to the mast cell B. The mast cell secretes IgE C. IgE secreted from plasma cell binds to the IgE receptor of mast cells D. Macrophages secretes leukotrienes E. Leukotrienes attract eosinophils to the site of inflammation 143.Which of the following statements regarding loose areolar connective tissue is CORRECT? A. There is an abundance of fibers and cells 149

B. The ground substance is calcified C. There is hardly any ground substance between the fibers and cells D. Reticular fibers and mast cells are the predominant components of loose areolar connective tissue E. It has lots of ground substance, abundance of cell types and scattered fibers 144.Which of the following statements regarding collagen biosynthesis is CORRECT? A. Initial glycosylation of specific hydroxylysyl residues occurs in the Golgi complex B. Removal of the signal peptide occurs after hydroxylation of specific proline and lysine residues in the rough endoplasmic reticulum C. Procollagen peptidase removes the registration peptides inside the cell D. Vitamin C is essential for the hydroxylation of proline residues in the rough endoplasmic reticulum E. The assembly of procollagen molecules i.e. the triple helix arrangement occurs in the secretory vesicles 145.Which of the following features regarding cartilage is CORRECT? A. Lymphatic vessels penetrate the cartilage matrix B. Nutrients for chondrocytes of cartilage are derived from blood capillaries found in the perichondrium C. The perichondrium that surrounds the cartilage is composed of collagen type II D. Nerve endings are found adjacent to chondrocytes E. Articular cartilage is covered by perichondrium 146.Which of the following statements regarding hyaline cartilage is CORRECT? A. Hyaluronic acid is a sulfated glycosaminoglycan and it binds to chondrocytes B. It is composed of collagen type I and elastic fibers C. The ground substance stains eosinophilic D. Chondronectin binds the cells to the collagen fibrils and glycosaminoglycans of proteoglycans E. Estradiol stimulates glycosaminoglycan synthesis 147.Which of the following components is NOT found in smooth muscle? A. Desmin B. Calmodulin binding protein C. Myosin D. Tropomysin E. Troponin 148.Which of the following statements is NOT CORRECT for cardiac muscle? A. T-tubules enter at the A-I junction of a sarcomere B. Mature cardiac muscle cells do not divide C. T-tubules and the sarcoplasmic reticulum form diads D. Ca++ are actively transported into the cell from the extracellular fluid E. The nucleus of cardiac muscle cell is centrally located 149. Which of the following statements regarding the hormonal control of osteoclast activity is CORRECT? A. Progesterone increases the activity of osteoclast cells to form new bone B. Calcitonin increases the activity of osteoclast cells to destroy bone C. Parathyroid hormone decreases the activity of osteoclast cells D. Parathyroid hormone increases the activity of osteoclast cells causing increase resorption of bone E. Parathyroid hormone influence osteoclast cells to make new bone 150.Which of the following statements regarding bone is CORRECT? A. The main organic component of bone is proteoglycans B. Most proteoglycans have glycosaminoglycans with acidic sulfated groups C. Bone stains basophilic due to the ground substance 150

D. Collagen type II is the main organic component E. Hydroxyapatite crystals are the main inorganic material of bone that bind to collagen type I 151.Which of the following processes is NOT part of the sequence of events that causes contraction of a skeletal muscle fiber? A. Depolarization of skeletal plasma membrane results in Na+ rushing into the cell B. Conduction of depolarization to the sarcoplasmic reticulum is via T-tubules C. The action potential triggers release of Ca++ from the sarcoplasmic reticulum D. The action potential triggers the intake of Ca++ from the extracellular matrix E. Ca++ binds to troponin allowing binding sites on actin to become available for the myosin heads 152.Which of the following statements concerning osteoblasts cells is CORRECT? A. They produce osteoid B. They secrete high quantities of acid phosphatase for mineralization of bone C. They sit within a lacuna D. They are involved in the destruction of bone E. They differentiate into chondrocytes 153.Which of the following statements concerning osteoclast cells is CORRECT? A. PTH stimulates osteoblasts to carry out osteogenesis B. Osteoclast stimulating factor stimulates calcitonin production C. Osteoclast stimulating factor is secreted by osteocytes D. Calcitonin inhibits the activity of osteoclast cells E. Calcitonin binds to the osteoblast cells which then secretes osteoclast stimulating factor 154.In long bone development: A. Osteoblast cells lay down new bone on the hypertrophic cartilage B. The bone collar forms by intramembraneous ossification C. The epiphyseal plate grows by appositional growth D. The calcified cartilage possesses chondrocyte cells E. The bone collar is produced by chondroblast cells 155.In the maturation of the polymorphonuclear leukocyte (PMN), the earliest recognizable cell to acquire granules is: A. Band cell B. Myeloblast C. Promyelocyte D. Metamyelocyte E. Segmented neutrophil 156.The inner mass of cells from the blastocyst stage of development eventually gives rise to: A. Morula B. Trophoblast C. Syncytiotrophoblast and cytotrophoblast D. Epiblast and hypoblast E. Zona pellucida 157.Which of the following statements regarding fertilization is CORRECT? A. Sperms that are incapacitated can penetrate the zona pellucida B. The zona pellucida normally blocks all sperms except one C. As soon as the sperm touches the oocyte plasma membrane, a zonal reaction takes place whereby the oocyte membrane and zona pellucida undergo a conformational change D. The cortical granules release enzymes that destroys a pathway in the zona pellucida for sperm entrance E. The sperm plasma membrane does not fuse with the oocyte plasma membrane 158. Intraembryonic mesoderm is derived from the A. amnioblast layer 151

B. hypoblast layer C. definitive yolk sac D. epiblast E. chorion 159.Epiblast cells that enter the primitive node gives rise to: A. Intraembryonic mesoderm that migrates around and in front of the prochordal membrane B. Notochordal rod that extends to the prochordal plate C. Endoderm that lines the digestive tube D. Prochordal plate E. Lateral plate mesoderm 160.Osteons…. A. have collagen fibers organized in regular parallel arrangement in each lamella B. are composed of osteoblast and osteogenic cells C. form the inner circumferential lamellae of compact bone D. are derived from osteoclast cells E. are Sharpey's fiber that leave the periosteum 161.During meiosis, the secondary spermatocytes have A. 4 N DNA B. 23 chromosomes C. 46 chromosomes D. 1 N DNA E. 46 chromosomes (2N DNA) 162.The posterior fontanelle is usually closed by A. birth B. age 6 months C. age 18 months D. age 2 years E. age 5 years 163.Which of the following statements is CORRECT concerning the third week of development? A. The notochord induces the overlying ectoderm to form the neural plate B. Paraxial mesoderm induces the overlying ectoderm to form the neural plate C. Sclerotomes form the muscles of the skeleton D. The primitive streak is a thickening of the hypoblast E. Myotomes form the bones of the ribs 164.The intraembryonic coelomic cavity located cranial to the oropharyngeal (buccopharyngeal) membrane becomes what structure? A. Pleural cavity B. Peritoneal cavity C. Mouth cavity D. Yolk sac E. Pericardial cavity 165.Calcitonin producing cells are derived from: A. Mesodermal cells B. Neural crest cells C. Ectodermal and mesodermal cells D. Neural tube cells E. Endodermal cells 166.Which of the following statements concerning cartilage is CORRECT? A. Isogenous groups are formed within the perichondrium B. Chondrocytes within the cartilage model divide and grow by appositional means C. Chondrogenic cells from the inner layer of the perichondrium differentiate into chondroblasts 152

D. Chondrocytes synthesize collagen type I E. The perichondrium is composed of collagen type II and elastic fibers 167.Which of the following properties is unique to cartilage? A. Hyaluronic acid form proteoglycan aggregates within the extracellular matrix B. Collagen type II fibrils are visible at the light microscopic level C. Osteonectin binds the cells of the cartilage matrix D. It has a preponderance of hydroxyapatite crystals E. A periosteum covers cartilage 168. Which of the following statements concerning the plasma membrane is CORRECT? A. Integrins are considered integral proteins B. Transmembrane proteins are peripheral proteins C. Integral membrane proteins are only found on the inner side of the lipid bilayer D. Peripheral proteins are embedded within the lipid bilayer E. Peripheral proteins are only found on the outer side of the plasma membrane 169. In coupled transport, symport refers to the process of transporting A. two different molecules in the same direction B. a molecule out of the cell via exocytosis C. a molecule into the cell via receptor mediated endocytosis D. two different molecules in the opposite direction E. Na+ into the cell 170. Which of the following statements concerning the glycocalyx is NOT CORRECT? A. Oligosaccharides project from the glycoproteins into the external aqueous environment (outside the cell) B. It is involved in cell to cell recognition C. It is found on the nuclear envelope D. It contains glycoprotein constituents E. It is involved in cell adhesion 171.Which of the following structures form the wall of the gut? A. Endoderm and somatic mesoderm B. Ectoderm and extraembryonic splanchnic mesoderm C. Endoderm and splanchnic mesoderm D. Ectoderm and somatic mesoderm E. Endoderm and neural crest cells 172.The lining of the intervillous spaces are A. composed of syncytiotrophoblast cells B. composed of syncytiotrophoblast, cytotrophoblast, mesenchyme and endothelial layer of blood capillaries C. composed of cytotrophpoblast cells D. filled with secondary chorionic villi E. composed of syncytiotrophoblast and endothelial layer of blood capillaries 173. Which organelle in the liver is involved in the detoxification of drugs? A. Rough endoplasmic reticulum B. Golgi complex C. Smooth endoplasmic reticulum D. Ribosomes E. Mitochondria 174. Which of the following statements concerning receptor mediated endocytosis is NOT CORRECT? A. Pinocytotic vesicles lose their clathrin coat and then fuse with early endosomal vesicles B. Clathrin molecules are digested by enzymes before uncoupling of ligand and receptor C. A ligand attaches to receptors on the outside of the plasma membrane

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D. Clathrin-coated endocytotic vesicles are formed. The clathrins face the cytosolic environment E. Acidification of the pinocytotic vesicle occurs by actively pumping H+. This causes uncoupling of the ligand and receptor 175. Which of the following cell types would contain many mitochondria in the apical portion of the cell? A. Ciliated pseudostratified epithelial cell B. Steriod secreting cell C. Pancreatic acinar cell D. Simple squamous epithelial cell E. Ion transporting cell that shows basal infolding 176.Which of the following statements regarding the nuclear envelope is NOT CORRECT? A. The inner membrane adjacent to chromatin is studded with ribosomes B. Macromolecules can pass from the nuclear matrix into the cytoplasm via nuclear pores C. Where nuclear pores are found, the inner and outer membranes of the nuclear envelope fuse D. Consist of two asymmetrical unit membranes E. Each nuclear pore complex is composed of a scoffold, transporter subunit, thick filaments and a basket 177.Which of the following statements is NOT considered to be significant to meiosis? A. Crossing over of genetic information during prophase I of meiosis I B. Pairing of homologous chromosomes during prophase I of meiosis I C. Independent assortment of maternal and paternal chromosomes D. Unequal cell size E. Non disjunction 178.Which of the following structures is involved in the formation of primordial germ cells? A. Septum transversum B. Somites C. Amnion D. Gonads E. Yolk sac 179.The notochordal rod (process) increases in length as a result of migration of cells from the A. primitive node B. endoderm C. primitive streak D. neural plate E. prochordal plate 180.In the third week of embryonic development primitive blood cells begin to form first in the A. liver B. yolk sac C. chorion D. amnion E. bone marrow 181.Which of the following statements concerning fertilization is NOT CORRECT? A. Sperms have to be capacitated in order to fertilize the secondary oocyte B. The sperm penetrates the corona radiata and then the zona pellucida C. Cortical granules are released as soon as the sperm touches the oocyte plasma membrane D. The zonal reaction allows other sperms to penetrate the oocyte E. The zonal reaction causes the zona pellucida to undergo a morphological change 182.Which of the following features regarding the second week of development is CORRECT? A. The lacunae spaces are formed in the primitive yolk sac

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B. Syncytiotrophoblast cells are involved in eroding maternal sinusoids to establish the primitive uteroplacental circulation C. Epiblast cells are involved in establishing the primitive uteroplacental circulation D. The cytotrophoblast layer erodes the maternal endometrium E. The hypoblast layer gives rise to the amnion 183.During the second week of development, the embryo proper is composed of A. amnion, yolk-sac, epiblast and hypoblast B. epiblast and hypoblast C. trophoblast cells D. syncytiotrophoblast and cytotrophoblast E. trophoblast, epiblast and hypoblast 184.The prochordal plate is a group of tall columnar cells that A. develop during the 8th day after fertilization B. are located within the amniotic sac C. determine the future site of the mouth cavity D. form the connecting stalk E. form the extraembryonic mesoderm 185.Which of the following cell types is involved in the production of placental estrogen? A. Decidua basalis B. Cytotrophoblast cells C. Yolk sac cells D. Extraembryonic somatic mesoderm E. Syncytiotrophoblast 186.At the time of ovulation the released egg is a secondary oocyte arrested at metaphase II of meiosis II the released egg is a primary oocyte arrested at prophase I of meiosis I the oocyte released is a primary oocyte FSH is responsible for stimulating ovulation corpus luteal cells are derived from the primary oocyte 187.Which of the following, statements concerning simple columnar epithelium is NOT CORRECT? A. It contains well developed junctional complexes or terminal bars B. It is found lining the small intestines C. It is found lining the epididymis D. All of its cells rest on a basal lamina E. All of its cells reach the apical level 188.Hemidesmosomes are located on the lateral surface of cells zonula adherens found on the basal surfaces that are involved in attaching integral proteins to the basal lamina found on the apical surface of cells composed in part of actin microfilaments 189.Which of the following statements regarding stratified squamous keratinized epithelium is NOT CORRECT? A. It is found covering the surface of the skin B. The basal layer of cells may be cuboidal or columnar and these cells rest on the basal lamina C. Some of its cells rest on the basal lamina D. Apical cells are squamous and dead E. Blood vessels penetrate this epithelium

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190.Which of the following statements concerning classification of exocrine glands is NOT CORRECT? A. The mode of secretion may be merocrine B. The method of secretion may be into the tissue spaces surrounding the secretory cells C. The nature of the duct system may be compound D. The shape of the secretory unit may be mucous E. The nature of the secretory product may be mucus 191. Which of the following statements concerning growing primary follicle is CORRECT? A. The granulosa layer of cells secrete androgens B. Fluid filled spaces appear between the granulosa layer of cells C. The zona pellucida is absent D. The theca externa layer of the cells rest on a basal lamina E. The granulosa layer of cells rest on a basal lamina 192. Eating poorly cooked pork may lead to infection with the roundworm Trichinella spiralis. This may cause mild gastrointestinal symptoms followed by periorbital edema, muscle pains, fever, and A. thrombocytosis B. basophilia C. eosinophilia D. neutrophilia E. erythrocytosis 193. Which of the following statements regarding loose connective tissue is NOT CORRECT? A. Tendon is an excellent example of loose connective tissue B. Is found beneath epithelia as in the lamina propria C. Has an abundance of cell types D. Is found around blood vessels and glandular units E. Has an abundance of ground substance within the tissue spaces 194. Which of the following statements concerning collagen biosynthesis is CORRECT? A. Specific proteases remove the registration peptide outside the cytoplasm of the fibroblast cell B. Hydroxylation of specific glycine residues takes place in the Golgi apparatus C. Glycosylation of hydroxyglycine molecules occurs in the RER D. Procollagen molecules are insoluble due to the registration peptide E. The tropocollagen molecule is composed of only 2 polypeptide chains 195. Your patient is anemic; on examination of the smear, you see anucleate erythrocytes averaging 5 microns in diameter, are very light in color, and many have basophilic portions of the cytoplasm. You describe this to your colleagues as: A. Macrocytic, hypochromic, basophilia, and a shift to the right B. Microcytic, hypochromic, reticulocytosis, and a shift to the left C. Normocytic, hyperchromic, leukocytosis, and a shift to the right D. Microcytic, hypochromic, eosinophilia, and a shift to the left E. Macrocytic, hypochromic, poikilocytosis, and a shift to the left 196. Which of the following statements concerning an allergic reaction is CORRECT? A. Antigens from pollen bind directly to mast cells causing them to secrete IgE antibodies B. Antibody IgE binds to fibroblast cells C. Adipose cells secrete IgG D. IgE antibodies secreted by plasma cells binds to the surface of mast cells E. Fibroblast cells secrete heparin and histamine 197. During the first six days of embryonic development: A. The zona pellucida disappears around the 5-6 day stage of development B. Blastomeres divide primarily by meiosis C. The morula has acquired a cavity that is filled with fluid 156

D. Blastomeres at the 8-cell stage not only divide by mitosis but increase in size E. The inner cell mass secretes human chorionic gonadotropin 198. During the second week of embryonic development: A. The embryo proper is referred to as a bilaminar germ disc B. The trophoblast layer forms the inner cell mass C. The cytotrophoblast layer secretes luteinizing hormone D. The amnion is connected to the hypoblast layer E. Syncytiotrophoblast gives rise to the secondary yolk sac 199. The primitive uteroplacental circulation occurs as a result of A. syncytiotrophoblast cells eroding the lining of maternal blood vessels and allowing the blood to enter the lacunae (spaces) B. blood vessels developing in the wall of the yolk sac C. cytotrophoblast cells forming lacunae (spaces) D. the inner cell mass developing blood vessels E. blood vessels forming in the extraembryonic mesoderm 200. At the time of ovulation, the developing egg is arrested at which stage of development? A. Leptotene stage of meiosis I B. Prophase 1 of meiosis 1 C. Zygotene stage of meiosis II D. Diplotene stage of meiosis I E. Metaphase stage of meiosis II 201. Which of the following cell types is present two years after birth? A. Primary spermatocytes B. Spermatids C. Spermatogonia D. Oogonia E. Secondary oocytes 202.The sarcoplasmic reticulum of a skeletal muscle is A. a type of rough endoplasmic reticulum B. a site of glycogen storage C. a site into which calcium is released during muscle relaxation D. a site of calcium - binding protein (calsequestrian) and a Ca++ - activated ATP pump E. not found surrounding myofibrils 203.Which of the following statements is CORRECT regarding cardiac muscle? A Gap junctions are absent B Triads are present at the A-I junction C Intercalated discs contain zonulae occludentes D Is capable of extensive regeneration E. Cells are long and possess many nuclei located under the sarcolemma 204. Which of the following cell types differentiates into macrophages? A. Neutrophil B. Fibroblast C. Chondroblast cell D. Plasma cell E. Monocyte 205. Which of the following processes is involved in the formation of the three germ layers? A. Angiogenesis B. Neural crest migration C. Neurulation D. Gastrulation E. Invagination of endodermal cells 157

206. During the formation of the trilaminar embryo, ectoderm and mesoderm are derived from: A. Chorion B. Hypoblast C. Amnioblasts D. Epiblast E. Exocoelomic (Heuser's) membrane 207. Which of the following statements regarding mesodermal cell migration is NOT CORRECT? A. The intraembryonic mesoderm becomes continuous with the extraembryonic mesoderm B. In front of the prochordal plate, the mesoderm forms the cardiogenic area C. The mesodermal cells between the prochordal plate and primitive knot form the notochordal rod (tube) D. Cells migrate in all regions between the epiblast and hypoblast E. Mesodermal cells on either side of the notochord form the paraxial mesoderm 208. Which of the following structures is derived from the ectodermal germ layer? A. The central nervous system B. The lining of the respiratory tract C. Muscle cells D. Lining of the digestive tube E. The kidney 209. Upon full contraction of the sarcomere, one of the characteristic bands will disappear, then reappear in the relaxed state, This is the A. M band B. Intercalated disc C. A band D. I band E. Z band 210.Myoblasts from the occipital myotomes are believed to give rise to the muscles of the: A. Ear B. Neck C. Tongue D. Eye E. Pharynx 211.Which of the following correlations is/are INCORRECT? A. Membranous neurocranium ---bones of face B. Clavicle ---1st bone to ossify C. Sutures ----fontanelles D. Anterior fontanelle ---close at 3 months post birth E. Head mesenchyme ---neural crest cells 212.In a histologic section of the spinal cord, rows of nuclei are seen between myelinated axons in the white matter. These nuclei are evidence of which cell type A. Microglia B. Astrocytes C. Ependymal cells D. Oligodendrocytes E. Schwann cells 213.Saltatory Conduction of nerve impulses is MOST LIKELY related to A. anterograde axonal transport B. nodes of Ranvier C. distribution of Nissl substance D. podocytic astrocytic processes 158 synaptic neurotransmissio 214. A 65-year-old woman with atrial fibrillation has a stroke of the left cerebral hemisphere due to occlusion of the left middle cerebral artery by an embolus. Over the next several months, scar tissue forms in the brain at the site of infarction. Which of the following cells is MOST LIKELY to have participated in forming this scar? A. Astrocytes B. Ependymal cells C. Microglia D. Oligodendroglia E. Schwann cells 215.A 37-year-old woman develops rapid progressive weakness and numbness involving her limbs over five days. on examination, she is diffusely weak and hyporeflexic. She has slowed conduction velocities and demyelination in her peripheral nerves. An immune attack on which of the following cells is the MOST LIKELY cause of her condition? A. Astrocytes B. Ependymal cells C. Microglia D. Oligodendroglia E. Schwann cells 216.Which of the following is derived from neural crest? A. Astrocytes B. Ependymal cells C. Microglia D. Oligodendroglia E. Schwann cells 217.Which of the following is derived neither from neural crest nor neural tube? A. Astrocytes B. Ependymal cells C. Microglia D. Oligodendroglia E. Schwann cells 218.The presence of desmin (intermediate filament) in an analysis of a tumor would suggest that it is present in A. mesenchymal cells B. muscle cells C. epithelium D. neuron E. glial (neuroglial) cells 219.Which of the following is found primarily in the lamina lucida of the basement membrane? A. Collagen type IV B. Laminin C. Microfibrils D. Collagen type VII E. Reticular fibers 220.Which of the following statements regarding hyaline cartilage is CORRECT? A. It has osteocalcin that binds the cells to the ground substance B. It contains osteocytes in lacunae C. It contains collagen type 1 fibrils D. It has lower levels of chondroitin-4-sulfate and chondroitin-6-sulfate E. Chondronectin binds the cells to the extracellular matrix 221.Which process is normally restricted to cartilage? 159

A. Formation of osteoblasts from the inner layer of periosteum B. Interstitial growth C. Formation of chondroblasts from the periosteum D. Intramembranous ossification E. Appositional growth 222.Which of the following statements regarding osteoclast cells isNOT CORRECT? A. Are derived from hemopoietic stem cells (monocytes) B. Are found in depressions of the bone matrix called Howship's lacunae C. Calcitonin hormone influences osteoclastic activity resulting in increased bone resorption D. They secrete proteolytic enzymes extracellularly for collagen degradation E. Are multinucleated cells with acidophilic cytoplasm 223.Which of the following statements regarding intramembranous bone formation is CORRECT? A. Cartilage cells becomes hypertrophic and then die as a result of calcification B. Flat bones of the skull first undergo first intramembranous ossification and this is followed by endochondral ossification C. Osteoblast cells arising from mesenchyme lay down bone intramembranously D. Bone grows interstitially E. Osteoblast cells deposit bone on calcified cartilage 224.The primitive streak that forms during the 3rd week of development: A. Has a primitive knot (node) that allows cells to migrate from the epiblast layer and form the notochord B. Does not allow any cells to migrate through the primitive streak C. Allows cells from the hypoblast layer to migrate and form the mesoderm D. Is derived from the hypoblast layer E. Allows mesodermal cells to migrate and become endodermal 225.Which organelle is primarily involved in drug detoxification such as phenobarbital? A. Smooth endoplasmic reticulum B. Mitochondria C. Rough endoplasmic reticulum D. Peroxisome E. Lysosome 226.The umbilical vein and arteries are derived from which of the following structures? A. Yolk sac B. Amnion C. Embryo proper D. Allantois E. Chorion 227.The bones of the vertebral column are derived from which of the following structures? A. Dermatomes B. Sclerotomes C. Myotomes D. Somatic mesodermal layer E. Neural crest cell 228.The decidual (placental) septa divides the fetal part of the placenta into several compartments. These septae are separated from the maternal blood and are covered by A. only cytotrophoblast cells B. only connective tissue mesenchyme C. chorion frondosum D. cytotrophoblast and syncytiotrophoblast E. simple columnar epithelial cells 229.In of the replacement of hyaline cartilage by bone, the bone collar the cartilage model is 160

A. derived from the transformation of the cartilage cells B. derived from calcified cartilage C. formed by intramembranous ossification D. formed by endochondral ossification E. formed by osteoblast cells laying down bone on calcified cartilage 230.Which of the following types of glycosaminoglycan is involved in forming proteoglycan aggregates? A. Perlacan B. Hyaluronic acid C. Chondroitin-4-sulfate D. Dermatan sulfate E. Keratan sulfate 231.The effect of norepinephrine on cardiac muscle is: A. A decrease in the velocity of conduction B. A decrease in the rate of contraction C. No effect; cardiac muscle is myogenic D. An increase in the rate of contraction E. To block troponin/tropomyosin sites 232.Cardiac muscle contraction differs from skeletal muscle mainly because of A. the difference in regulatory proteins B. the presence of myosin light chain kinase C. the differences in motor end plates D. intercellular contacts and calcium sources for contraction E. the lack of cardiac muscle troponin 233.Most blood transfusion reactions are due to clerical error. You order a packed cell transfusion for your patient who is Type A; the donor cell container is labeled Type 0. Your next action would be to: A. Stop; the patient can only receive Type B blood cells B. Stop; the patient can only receive Type AB blood cells C. Proceed, as no agglutination is likely to occur D. Stop; the patient can only receive Type A blood cells E. Proceed; the patient can receive all types of blood cells 234.Tapping the quadriceps tendon of the knee joint with a reflex hammer is a routine part of the physical examination. This patellar reflex A. involves the muscle spindle; stretching it results in inhibition B. involves the muscle spindle; stretching it results in contraction C. involves the Golgi tendon organ; stretching it results in contraction D. involves the Golgi tendon organ; tension results in contraction E. involves the contraction of the Golgi tendon organ 235.Your patient is a 30 year-old woman who complains of dysphagia (difficult swallowing), diplopia (double vision), and weakness in her arms. You notice ptosis (droopy eyelids). On administration of intravenous edrophonium, an anticholinesterase drug of short action, instant improvement is noted. This effectively locates the problem: A. On the cell membrane of smooth muscle cells B. At the myoneural junction of skeletal muscle cells C. At the myoneural junction of smooth muscle cells D. In the intracellular compartment of skeletal muscle cells E. Within the axon of the motor end plate 236.In sickle cell crisis, one would expect to see peripheral blood smears that exhibit: A. Reticulocytopenia B. Proerythroblasts C. Polycythemia 161

D. Hyperchromic cells E. Poikilocytosis 237.Which of the following statements concerning transverse tubules is CORRECT? A. They form part of the skeletal muscle diad B. They are present in smooth muscle cells C. They are extensions of the sarcolemma D. They are extensions of the sarcoplasmic reticulum E. They serve to sequester calcium ions 238. Which of the following statements concerning the basic structure of biological membranes is CORRECT? A. It is visualized as a trilaminar structure with the (transmission) election microscope B. It possesses a membrane of 0.5 to 1 um in thickness C. At the E.M. level, the internal membranes differ from the external membranes of the cell D. It is best described as lipids dispersed within a protein bilayer E. The plasma membrane can be visualized at the light microscopic level 239.Which of the following statements regarding skeletal muscle is CORRECT? A. Thick filaments are composed of actin, troponin and tropomyosin B. Thick filaments are composed of actin and tropomyosin only C. Thin filaments are composed of myosin protein D. Elastic filaments, made of the protein titin, anchors the thick filaments E. Elastic filaments, made of protein titin, anchors the thin filaments 240.Which of the following statements regarding skeletal muscle is CORRECT? A. An action potential flows down the T-tubule and releases Ca++ from the swollen ends of diads B. Terminal cisternae of SR form triads with T-tubules C. Ca++ are obtained for each contraction from the extracellular space D. Sarcoplasmic reticulum surrounds individual myofilaments E. Mitochondria are only located beneath the plasma membrane 241.Which of the following structures regarding cardiac muscle is NOT CORRECT? A. Cardiac muscle cells branch and possess centrally located nuclei B. The cells display cross striations C. Triads are a common feature of this tissue D. Intercalated discs are present in this tissue type E. Ca++ are actively transported from the extracellular fluid 242.Which of the statements regarding smooth muscle is NOT CORRECT? A. Dense bodies are connected to plasma membrane B. Dense bodies are associated with intermediate filaments C. Sarcolemmal vesicles function in sequestering Ca++ D. T-tubules invaginate from the plasma membrane to the sarcoplasmic reticulum E. Thin filaments lack troponin 243. Which of the following statements describes the functional characteristics of lysosomes? A. The enzymes within the lysosomes lack specificity B. Primary lysosomes upon fusing with a phagosome produces a digestive vacuole or secondary lysosome C. They only function with the phagocytic pathway of the cell D. They function at alkaline pH E. Catalases are present in large quantities 244. The presence of cytokeratin in an analysis of a tumor would suggest that it is present in A. mesenchyme B. neurons C. epithelium D. connective tissue 162

E. endoderm 245. Which of the following events occurs in rough endoplasmic reticulum during synthesis of protein for export? A. The ribosome translates information from tRNA B. A signal recognition particle binds to the signal peptide as it emerges from the ribosome C. A signal recognition particle is sequestered in the ER membrane D. A docking protein binds to the signal peptide (sequence) as it emerges from the ribosome E. The signal peptide is not cleaved in the production of the protein molecule 246. During receptor mediated endocytosis, low density lipoprotein (a ligand) is dissociated from its receptor in the: A. Transport vesicle B. Endosome C. Non-clathrin coated vesicle D. Lysosome E. Clathrin-coated vesicle 247.Inclusion cell disease (I-cell disease) is characterized by the absence of hydrolytic enzymes from lysosomes. The MOST LIKELY cause for this defect is A. absence of an enzyme which adds mannose - 6 - phosphate to the lysosomal enzymes B. genetic mutations in the genes enclosing the hydrolases C. faulty ribosome D. missorting of lysosomal enzymes E. excessive production of acid phosphatases 248.Which of the following proteins binds to membrane proteins and serves as a scaffold to support the nuclear envelope? A. Actin B. Integrins C. Microtubules D. Lamins E. Spectrin 249.The function of microvilli is A. uptake of macromolecules B. increase in surface area for absorption C. cellular movement D. transport of intracellular organelles E. movement of substances over the cell surface 250.Which of the following contributes to epithelial polarity? A. Presence of an intact basal lamina B. Gap junctions C. Membrane fluidity D. Presence of desmosomes E. Location of golgi apparatus near the nucleus 251.Which of the following is found primarily in the lamina densa of the basement membrane? A. Entactin B. Type IV collagen C. Microfibrils D. Laminin E. Reticular fibers 252.Which of the following statements is CORRECT for epithelia? A. They are incapable of performing absorptive functions B. Certain types may contain apical specializations 163

C. They are surrounded by an abundance of extracellular matrix D. They demonstrate weak adhesion between cells E. They are highly vacularized 253. Which structure is involved in initiating the formation of hydroxyapathic crystals? A. Matrix vessicles of osteoblast cells B. Osteoid of osteocytes C. Elastic fiber D. Matrix vesicles of osteoclast E. Osteoid of osteoblast 254.Plasma cells are derived from which of the following? A. Macrophages B. Fibroblast C. T-lymphocytes D. Monocytes E. B-lymphocytes 255.On the basal side of the cell, the cytoskeleton of the cell communicates with the extracellular matrix across the plasma membrane by means of A. cadherins B. integrins C. proteoglycans D. microtubules E. tonofilaments 256.Hydroxylation of proline and lysine residues in collagen biosynthesis occurs A. outside the cell B. primarily in the golgi apparatus C. in the RER D. in coated vesicles that are transported from the Golgi to the plasma membrane E. in the formation of the tropocollagen molecule 257.Which of the following binds to the surface of the mast cells? A. Heparin B. Major basic protein C. Ig B D. Ig A E. Lactoferrin 258.Desmosine and isodesmosine are amino acids unique to certain fibers. They confer their property through the cross-linking of A. elastin B. type IV collagen C. microfibrils D. microtubules E. type I collagen 259.Which of the following statements concerning meiosis is CORRECT? A. Separation of chromatids occurs during anaphase I of melosis I B. Pairing of homologous chromosomes occurs in prophase II of meiosis II C. The genetic material in each of the four cells produced are identical D. Crossing over of genetic material occurs in prophase I of melosis I E. Non-disjunction cannot occur in meiosis I 260.Osteoblast cells are involved in A. production of collagen type II B. destruction of collagen type II C. formation of type 1 collagen, proteoglycan and glycoproteins D. formation of calcified cartilage 164

E. formation of the territorial matrix 261.Which of the following statements regarding bone is CORRECT? A. Parathyroid hormone inhibits osteoclast activity causing reduced bone resorption B. Parathyroid hormone stimulates osteoclastic activity causing increased bone resorption C. Calcitonin hormone stimulates osteocytes to become osteoblasts D. Parathyroid hormone influences osteocytes cells to form bone E. Calcitonin hormone stimulates osteoclastic activity causing increased bone resorption 262.Which of the following statements regarding mature bone is CORRECT? A. It has more cells than primary bone B. Collagen fibers are randomly arranged in lamellar bone C. It lacks osteons D. There is a parallel arrangement of collagen fibers in each concentric lamella E. Osteoclast sends out cytoplasmic processes that are housed in canalicul 263.Which of the following statements concerning development of the zygote is CORRECT? A. The morula loses its corona radiata and implants unto the endometrium B. The outermost layer of the blastocyst develops into a cytotrophoblast layer C. At around 5-6 days, the blastocyst loses its zona pellucida and implants onto the endometrium D. The zygote undergoes several meiotic divisions E. The inner cell mass of the morula gives rise to syncytiotrophoblast and cytotrophoblast 264.Which of the following statements is CORRECT during the 2nd week of embryonic development? A. The amnion forms from the hypoblast B. The inner cell mass differentiates into ectoderm, mesoderm and endoderm C. The prochordal plate develops from the hypoblast D.The trophoblast gives rise to the epiblast and hypoblast E. Placenta praevia refers to the development of the bilaminar germ disc 265.A 26-year-old woman with a history of visual loss recently developed left arm numbness and was brough to the emergency department. On examination, she had bilateral optic disc pallor, an internuclear ophthalmoplegia, hyperreflexia and left arm sensory loss. T1-weighted MR scan of the brain was obtained. An immune attack on which of the following cells is the MOST LIKELY cause of her condition? A. Microglia B. Oligodendroglia C. Astrocytes D. Ependymal cells E. Schwann cells 266. Which of the processes establishes the three definitive germ layers? A. Angiogenesis B. Cranio-caudal folding C. Gastrulation D. Neurulation E. Notochordal formation 267. Red blood cells (RBC) circulating in the blood are removed by macrophages as a result of A. lack of mitochondria in RBC B. defective oligosaccharides on the plasma membrane C. lysosomal enzyme activity in RBC D. inability of RBC to produce normal hemoglobin E. lack of cytoplasmic enzymes in RBC 268. Which of the following cell types is involved in the phagocytosis of antigen-antibody complexes? 165

A. Neutrophils B. Eosinophils C. Basophils D. Fibroblasts E. Lymphocytes 269. Which of the following statements regarding cartilage is CORRECT? A. Proteoglycans lack acidic S04 groups B. Proteoglycan aggregates link to hyaluronic acid interact with collagen type II C. A perichondrium encloses fibrocartilage D. Appositional growth occurs within the central part of the cartilage model E. A perichondrium covers articulating cartilage 270.Which of the following cell types is involved in producing testosterone during fetal development? A. Spermatogonia B. Leydig cells C. Stromal (C.T.) Cells of the ovary D. Primordial follicles E. Sertoli cells 271. The intraembryonic mesoderm divides the lateral plate mesoderm into A. paraxial and intermediate mesoderm B. somatic and splanchnic mesoderm C. gonads and kidneys D. somatic mesoderm and extraembryonic mesoderm E. somites and dermatomes 272. As a result of the cranio-caudal and lateral foldings of the embryo, the hindgut that is formed is lined by A. amnion B. endoderm C. extraembryonic mesoderm D. allantois E. mesoderm 273.In the development of the female gonads, the primordial germ cells that migrate from the yolk sac gives rise to A. oogonia B. spermatogonia C. sertoli cells D. leydig cells E. primary spermatocytes 274.The anterior two thirds of the tongue is derived from pharyngeal arch A. four B. one C. two D. three E. five 275.In sickle cell disease, the abnormal red blood cells A. are primarily reticulocytes B. do not complete differentiation from the bone marrow C. are inflexible, rigid and fragile D. lack hemoglobin E. have a biconcave shape

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276.Recent studies of stroke and other brain injuries have implicated glutamate as a major contributor to injury, a process termed "excitotoxicity". Which of the following cells play a major role in clearing glutamate from the brain under normal circumstances? A. Epithelial cells B. Microglia C. Ependymal cells D. Astrocytes E. Oligodendrocytes 277. During the 3rd week of development, the notochordal cells are derived from: A. Epiblast cells that migrate into the primitive streak B. Epiblast cells that migrate to the primitive node (knot) C. Prochordal plate D. Hypoblast cells E. Hypoblast cells migrating into the mesoderm 278.During neurulation, the neuroectodermal cells that delaminate to form neural crest cells give rise to A. the intraembryonic mesoderm B. autonomic ganglia C. the notochord rod D. the ectodermal layer E. somites 279.Barrett's esophagus is an esophageal epithelium, which is in nature: A. Stratified squamous non-keratinized B. Stratified columnar C. Stratified squamous keratinized D. Simple columnar E. Simple squamous 280.The organic matrix of dentin is secreted by A. odontoblasts B. megakaryoblasts C. ameloblasts D. osteoblasts E. enamalins 281. During the final stages of fetal development (5 months to term) the placental barrier is composed of A. syncytiotrophoblast and endothelial of fetal capillaries B. cytotrophoblast and endothelial of fetal capillaries C. syncytiotrbphoblast, cytotrophoblast, mesenchyme and endothelial of fetal capillaries D. decidua basalis, syncytiotrophchlast and cytotrophoblast E. decidua parietalis and chorionic frondosum 282. Which one of the following substances crosses the placental barrier? A. IgA B. Hormones from the pituitary gland C. Maternal cholesterol D. IgG E. Maternal phospholipids 283. Which of the following structures gives rise to the umbilical arteries and vein? A. The allantois B. The yolk sac C. Chorion D. The chorion frondosum E. Amnion

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LITERATURE

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