General Histology Lect1+2 2Nd Grade

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

The circulatory system pumps and directs blood cells and substances carried in blood to all tissues of the body. It includes both the blood and lymphatic vascular systems, and in an adult the total length of its vessels is estimated at between 100,000 and 150,000 kilometers. The blood vascular system, or cardiovascular system, consists of the following structures: (Heart, Arteries, Capillaries, and Veins)

Two major divisions of arteries, microvasculature, and veins make up the pulmonary circulation, where blood is oxygenated in the lungs, and the systemic circulation, where blood brings nutrients and removes wastes in tissues throughout the body.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

o HEART Cardiac muscle in the four chambers of the heart wall contracts rhythmically, pumping the blood through the circulatory system. The right and left ventricles propel blood to the pulmonary and systemic circulation, respectively; right and left atria receive blood from the body and the pulmonary veins, respectively.

The walls of all four heart chambers consist of three major layers 1. The internal endocardium: Consists of a very thin inner layer of endothelium and supporting connective tissue, a middle myoelastic layer of smooth muscle fibers and connective tissue, and a deep layer of connective tissue called the subendocardial layer that merges with the myocardium. Branches of the heart’s impulse-conducting system, consisting of modified cardiac muscle fibers, are also located in the subendocardial layer 2. The middle myocardium The thickest layer, consists mainly of cardiac muscle with its fibers arranged spirally around each heart chamber. Because strong force is required to pump blood through the systemic and pulmonary circulations, the myocardium is much thicker in the walls of the ventricles, particularly the left, than in the atrial walls 3. The external epicardium Is a simple squamous mesothelium supported by a layer of loose connective tissue containing blood vessels and nerves.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

The vessels between arterioles and venules can be any of three types. (a) Continuous capillaries, the most common type, have tight, occluding junctions sealing the intercellular clefts between all the endothelial cells to produce minimal fluid leakage. All molecules exchanged across the endothelium must cross the cells by diffusion or transcytosis. (b) Fenestrated capillaries also have tight junctions, but perforations (fenestrations) through the endothelial cells allow greater exchange across the endothelium. The basement membrane is continuous in both these capillary types. Fenestrated capillaries are found in organs where molecular exchange with the blood is important, such as endocrine organs, intestinal walls, and choroid plexus. (c) Sinusoids, or discontinuous capillaries, usually have a wider diameter than the other types and have discontinuities between the endothelial cells, large fenestrations through the cells, and a partial, discontinuous basement membrane. Sinusoids are found in organs where exchange of macromolecules and cells occurs readily between tissue and blood, such as in bone marrow, liver, and spleen.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

Lymphatic System Functions: 1. Reclaim lost fluid (3L) for return to cardiovascular system 2. Fat absorption from the digestive tract by special lymphatic vessel called lacteal which located in the lining of the small intestine, lymph passing through these lymphatic vessel has milky appearance because of its fat content and is called chyle. 3. Protect against pathogens & cancer cells:- → nonspecific defenses: general protection, does not distinguish threat specifics → specific defenses = immune response, identify and defend against one particular threat. Lymphatic System Components: 1. Lymph: fluid similar to plasma but less proteins.

- lymph originates as fluid lost from blood capillaries - collected in blind end lymphatic capillaries - overlapping endothelial cells create one way mini- valves - fluid, solutes, large objects driven into lymphatic capillary by pressure in interstitial space (arteries, skeletal muscle)

2. Lymphatic vessels: carry lymph from tissues to veins.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

Lymphatic capillaries, They begin as small, dead-end tubes called, excess fluid passes through spaces and enters lymphatic capillaries to become lymph, lymphatic capillaries are in almost all tissue of the body, with the exception of the central nervous system, the bone marrow, and tissue without blood vessels, such as cartilage, epidermis, and the cornea. Lymphatic capillaries differ from blood capillaries in that the lack a basement membrane and the cells of the cells of the simple squamous epithelium slightly overlap and are attached loosely to one another, two things occur as a result of this structure:

❖ Lymphatic capillaries are far more permeable than blood capillaries and nothing in the interstitial fluid is excluded from the lymphatic capillaries ❖ Lymphatic capillaries epithelium functions as serious of one-way valves (allow fluid to enter capillary but prevent it from passing back into the interstitial spaces

- The lymphatic capillaries join to form larger lymphatic vessels which resemble small veins, consist of three tunics: o Tunica intima consist of endothelium surrounded by an elastic membrane. o Tunica media consists of smooth muscle cells and elastic fibers. o Tunica adventitia thin layer of fibrous connective tissue. - Large ones have vasa vasorum. - Many valves (beaded appearance). - Many anastomoses. - Lymph nodes present along vessels. lymphatic capillaries → lymphatic collecting vessels →lymphatic trunks→ lymphatic ducts →subclavian veins

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Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

3. Lymphocytes and Phagocytes: provide defense. Lymphoid cells: Macrophages: phagocytosis and T cell activation - Dendritic cells: antigen presentation (found in CT) - Lymphocytes: (3 classes) 1. T cells - “Thymus dependent”, 80% - cytotoxic T cells: kill “foreign” cells directly (cell mediated immunity). - helper T cells: activate T & B cells. - suppressor T cells: inhibit T & B cells. 2. B cells - “Bone marrow derived”, 10-15%, - when activated →plasma cell. → secretes antibodies, antibodies bind specific antigens (foreign molecules) (antibody mediated or humoral immunity). 3. Natural Killer Cell: 5-10%, attack abnormal cells: cancer cells, or virus- infected cells (nonspecific defense).

4. Lymphoid tissues and organs: site of development of lymphocytes and screening for pathogens. Lymphoid Tissue - reticular CT & lymphocytes & other lymphoid cells - functions: 1- Proliferation site for lymphocytes 2- Surveillance point for lymphocytes and macrophages - two types: lymphoid follicles and lymphoid organs: 1- Lymphoid Follicles / Nodules - CT packed with lymphocytes (T, B, and dendritic cells) - No capsule - Germinal centre in middle: dividing B cells - Germinal centre surrounded by dendritic cells, T cells and some macrophages - Follicles associated with respiratory, digestive, and urinary tracts - special lymphoid nodule/follicle collections:

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

A. MALT (mucosa- associated lymphoid tissue): deep to intestinal epithelium, made up of individual nodules called Peyer’s Patches

B. Appendix , beginning portion of large intestine

C. Tonsils: large nodules in pharynx, have crypts to trap bacteria→encourage development of immunity 5 Total: palatine tonsils (2) pharyngeal (adenoid) (1) lingual tonsils (2)

Lymphoid Organs - have fibrous CT capsule around outside - contain many lymphoid follicles - include: lymph nodes, thymus, and spleen A. Lymph nodes: - Each lymph node filters lymph and provides a site for B-cell activation and differentiation to antibody-secreting plasma cells. - bean shaped, 1-25mm - structure: - capsule: CT, surrounds outside - trabeculae: folds of capsule creating partitions inside - superficial cortex =lymphoid follicles: B cells & dendritic cells

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

- Underlying paracortex (deep cortex) = Most lymphocytes enter at the paracortex of the lymph node via high endothelial venules (HEVs) located there only; most lymphocytes in this region are T helper cells. - Inner medulla = centre: houses T, B & plasma cells, the medulla has medullary cords containing reticular fibers with many plasma cells, macrophages, and other leukocytes; between the cords are lymph-filled medullary sinuses that converge at the efferent lymphatic.

(A) The medulla of a lymph node consists (B) Higher magnification of a medullary cord mainly of the medullary sinuses (MS) (MC) shows plasma cells (arrows) with separated by intervening medullary cords spherical, eccentric nuclei and much more (MC). Lymphocytes and plasma are abundant cytoplasm than lymphocytes. and predominate in number over other cell types.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

High endothelial venules (HEVs) : Specialized postcapillary venules in the paracortex, represent an important entry point for most (90%) lymphocytes into lymph nodes.

Lymph flow through node: lymph enters via afferent vessels (many), flows slowly through sinuses where it is surveyed for pathogens and antigens - Macrophages engulf pathogens - Dendritic cells bind antigens and stimulate lymphocytes “clean” lymph exits via efferent vessels (few) - If pathogen detected: lymphocytes increase in number (rapid clonal division of B & T cells) - causes node to swell = buboes , (Yersinia pestis → Bubonic plague)

B. Thymus - soft, lobulated lymphoepithelial organ, located superior to heart - The thymus gland is surrounded by a connective tissue capsule, under which is a dark-staining cortex with an extensive network of interconnecting spaces. These spaces become colonized by immature lymphocytes that migrate here from hemopoietic tissues in the developing individual to undergo maturation and differentiation.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

- T cells mature in cortex and migrate to medulla to enter blood - Thymus produces hormones: - thymosin & thymopoietin - both promote development and maturation of lymphocytes (mostly the T cells in thymus) - Thymus most active in early childhood, atrophies with age - The epithelial cells of the thymus gland provide structural support for the increased lymphocyte population. In the lighter-staining medulla, the epithelial cells form a coarser framework that contains fewer lymphocytes and whorls of epithelial cells that combine to form thymic (Hassall’s) corpuscles.

o Spleen

➢ The capsule (C) of the spleen connects to trabeculae (T) extending into the pulp-like interior of the organ. The red pulp (R) occupies most of the parenchyma, with white pulp (W) restricted to smaller areas,

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

➢ White pulp , only 20% of the spleen, is secondary lymphoid tissue associated with small central arterioles that are also enclosed by periarteriolar lymphoid sheaths (PALS) of T cells ➢ Names of these splenic areas refer to their color in the fresh state: red pulp is filled with blood cells of all types, located both in cords and sinuses; white pulp is lymphoid tissue. ➢ Blood flow in red pulp is either a closed circulation , moving from capillaries into the venous sinusoids, or an open circulation , with capillaries opening directly into the splenic cords. ➢ Blood filtration in the open circulation involves interaction with splenic cord macrophages that remove old, swollen RBCs unable to slip between stave cells to reenter the venous blood flow.

Blood flow in the spleen.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect1+2 2nd grade

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect3 2nd grade

Histology of the nervous system –part1- The nervous system is an integrated communication network; is formed by a network of many billion nerve cells ( neurons ), all assisted by many more supporting cells called glial cells . Each neuron has hundreds of interconnections with other neurons, forming a very complex system for processing information and generating responses. • Anatomically, the general organization of the nervous system has two major divisions: 1. Central nervous system (CNS) : -Brain and spinal cord. - Integration and command centre. 2. Peripheral nervous system (PNS): - Paired spinal and cranial nerves + group of nerve cells called ganglia. - Carry messages to and from the spinal cord and brain.

Characteristics of the Nervous Tissues Functions 1. Respond to environmental changes 1) Reception of information from the (stimuli). external and internal environment. 2. It has a special type of C.T called 2) Integration & analysis of the incoming neuroglia. information. 3. Characterized by conductivity, 3) Generation of new signals. excitability. 4) Conduction of these neural messages to 4. The nerve cell has 2 ends: the special responding tissues (effector • Multiple short endings (dendrites) regions). • Single long ending (Axon) 5. The axons are called nerve fibers (extend across the peripheral nerves).

➢ Neurons respond to environmental changes (stimuli) by altering the ionic gradient that exists across their plasma membranes. All cells maintain such a gradient, also called an

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect3 2nd grade

electrical potential, but cells that can rapidly change this potential in response to stimuli (eg, neurons, muscle cells, some gland cells) are said to be excitable or irritable. Development of nerve tissue • Ectodermal in origin.

• The human embryo during the fourth week of development show stages in the process of neurulation, the embryonic process by which cells of the CNS and PNS are initially produced.

• Neural plate → neural groove → neural tube.

• Cells lateral to the neural groove → neural crest → migrate → peripheral nervous system + other structures (chromaffin cells of the adrenal medulla + skin melanocytes + odontoblasts +

Schwann & satellite cells).

The functional unit in both the CNS and PNS is the neuron or nerve cell. Most neurons consist of three main parts: 1. The cell body (or perikaryon): which contains the nucleus and most of the cell’s organelles and serves as the synthetic or trophic center for the entire neuron. The perikaryon also contains basophilic Nissl substance or Nissl bodies, which are large masses of free polysomes and RER and indicate the cell’s high rate of protein synthesis. 2. The dendrites: which are the numerous elongated processes extending from the perikaryon and specialized to receive stimuli from other neurons at unique sites called synapses. 3. The axon (Gr. axon, axis): usually conduct action potential away from the cell body, much longer than dendrites, with constant diameter.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect3 2nd grade

Type of neurons: • Neurons can be classified according to the number of processes extending from the cell body: 1. Multipolar neurons, which have one axon and two or more dendrites (Interneurons and motor neurons are multipolar).

2. Bipolar neurons, with one dendrite and one axon (are found as components of sensory organs).

3. Unipolar or pseudounipolar neurons, which have a single process that bifurcates close to the perikaryon, with the longer branch extending to a peripheral ending and the other toward the CNS. (Most sensory neurons are unipolar).

4. Anaxonic neurons, with many dendrites but no true axon, do not produce action potentials, but regulate electrical changes of adjacent neurons. Anaxonic neurons are found in the brain, retina, and adrenal medulla. In the retina, they help in visual processes such as the perception of contrast.

Types of neuron according to their function: 1- Motor (efferent): control effector organs such as muscle 2- Sensory (afferent) : involve in the reception of sensory stimuli 3- Interneuron: About 90% of human neurons are interneurons. The word interneuron refers to the fact that they lie between, and interconnect, the incoming sensory pathways and the outgoing motor pathways of the CNS

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect3 2nd grade

(establish relationship among other neurons, forming functional network or circuits).

Note: ✓ Bipolar neurons are found in the retina, olfactory mucosa, and the (inner ear) cochlear and vestibular ganglia, where they serve the senses of sight, smell, and balance, respectively. ✓ Pseudounipolar neurons are found in the spinal ganglia (the sensory ganglia found with the spinal nerves) and in most cranial ganglia. ✓ Axons originate from a pyramid-shaped region of the perikaryon called the axon hillock, ✓ The plasma membrane of the axon is often called the axolemma and its contents are known as axoplasm. ✓ In contrast to dendrites, the typical axon is much longer, has a constant diameter, and branches less profusely. the distal end of an axon forms a terminal arborization, ✓ axons of interneurons and some motor neurons have branches called collaterals that end at synapses influencing the activity of many other neurons. ✓ Each branch ends with a dilation called a terminal bouton (synaptic knob) that contacts another neuron or non-nerve cell at a synapse to initiate an impulse in that cell.

Synapses (Gr. synapsis, union) are sites where nerve impulses are transmitted from one neuron to another or from neurons and other effector cells. The structure of a synapse ensures that transmission is unidirectional. Synapses convert an electrical signal (nerve impulse) from the presynaptic cell into a chemical signal that affects the postsynaptic cell.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect3 2nd grade

Types of Synapses Chemical Synapses Electrical synapse

Synapses convert an electrical signal (nerve - Gap junction between two cells , impulse) from the presynaptic cell into a chemical Transmit ionic signals through gap signal that affects the postsynaptic cell. junction that cross the pre- and A synapse has the following components: postsynaptic membranes 1. Presynaptic axon terminal (terminal bouton) from which neurotransmitter is released by exocytosis - It is faster than chemical synapse. from synaptic vesicles. 2. Postsynaptic cell membrane with receptors for the transmitter and ion channels or other mechanisms to initiate a new impulse. 3. A 20- to 30-nm-wide intercellular space called the synaptic cleft separating the presynaptic and postsynaptic membranes.

Morphologically, various types of synapses are seen between neurons: • If an axon forms a synapse with a cell body, it is called an axosomatic synapse; with a dendrite, axodendritic; or with another axon, axoaxonic. • Axoaxonic synapses modulate activity of the other two types.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect3 2nd grade

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect4 2nd grade

Histology of the nervous system –part2-

Glial cells (neuroglia) support neuronal survival and activities, and are ten times more abundant in the mammalian brain than the neurons. ➢ Except around the larger blood vessels, the CNS has only a very small amount of connective tissue and collagen. Glial cells substitute for cells of connective tissue in some respects, supporting neurons and creating a microenvironment immediately around those cells that is optimal for neuronal activity. ➢ The fibrous intercellular network surrounding cells of the CNS may superficially resemble collagen with light microscopy, but it is actually the network of cellular processes emerging from neurons and glial cells. Such processes are collectively called the neuropil

CNS ; glial cells 1- Oligodendrocyte: myelinate parts of several axons 2- Astrocyte: Multiple processes and form perivascular feet that completely enclose all capillaries, two types: Fibrous astrocytes Protoplasmic astrocytes Few, long processes and found Many, short processes and in white matter found in gray matter

3- Ependymal cells: epithelial-like cells that line the ventricles and central canal 4- Microglia: have a protective, phagocytic, immunerelated function

PNS; glial cells 1- Schwann cell: forms myelin around a segment of one axon, in contrast to the ability of oligodendrocytes to branch and ensheath parts of more than one axon 2- Satellite cells : are restricted to ganglia where they cover and support the large neuronal cell bodies.

“CENTRAL NERVOUS SYSTEM” CNS is covered by three connective tissue layers, the meninges 1- Dura Mater: The thick external, consists of dense, fibroelastic connective tissue that is continuous with the periosteum of the skull, Around the spinal cord, the dura mater is separated from the periosteum of the vertebrae by the epidural space. The internal surface of all dura mater, as well as its external surface in the spinal cord, is covered by simple squamous epithelium of mesenchymal origin.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect4 2nd grade

2- Arachnoid: has two components: (1) a sheet of avascular connective tissue (lacks nutritive capillaries) in contact with the dura mater and (2) a system of loosely arranged trabeculae composed of collagen and fibroblasts, Surrounding the trabeculae is a large, sponge-like cavity, the subarachnoid space, filled with CSF (helps cushion and protect the CNS from minor trauma). 3- Pia Mater: Consists of flattened, mesenchymally derived cells closely applied to the entire surface of the CNS tissue. The pia does not directly contact nerve cells or fibers, being separated from the neural elements by the very thin superficial layer of astrocytic processes (the glia limitans), which adheres firmly to the pia mater. Together, the pia mater and the layer of astrocytic end feet form a physical barrier separating CNS tissue from CSF in the subarachnoid space

❑ The choroid plexus ; folds projecting into the four large ventricles of the brain, each villus of the choroid plexus contains a thin layer of well-vascularized pia mater covered by cuboidal ependymal cells. The function of the choroid plexus is to transport of water and ions across the capillary endothelium and ependymal layer and the elaboration of these as CSF.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect4 2nd grade

❑ In some areas, the arachnoid penetrates the dura mater and protrudes into blood- filled venous sinuses located within that layer. These CSF-filled protrusions, which are covered by vascular endothelial cells lining the sinuses, are called arachnoid villi, which function as a site for absorption of CSF into the blood of the venous sinuses (There are no lymphatic vessels in CNS tissue).

• The entire CNS displays organized areas of white matter and gray matter, differences caused by the differential distribution of myelin. White matter Gray matter 1. Bundles of axons each coated with a 1. Masses of cell bodies and dendrites , the sheath of myelin, oligodendrocytes with initial unmyelinated portions of axons, very few neuronal cell bodies but astrocytes, and microglial cells. astrocytes and microglia are present 2. 2. Myelin is responsible for the white 3. A grey color because of the grey nuclei appearance of the white matter. that comprises the cells. 4. In spinal cord, the gray matter inside and 3. In spinal cord, the white matter is at the in the brain is outside surface and in the brain is at inside.

• The cerebellar cortex, which coordinates muscular activity throughout the body, also has a layered organization 1. an outer molecular layer (ML), 2. a central layer of very large neurons called Purkinje cells (P) 3. an inner granule layer (GL). Note : • Neuroscientists recognize six layers of neurons with different sizes and shapes in the cerebral cortex. The most conspicuous of these cells are the efferent pyramidal neurons that come in many sizes ( lab 3)

cerebellar cortex

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect4 2nd grade

Blood-Brain Barrier(BBB): In most CNS regions, neurons are also protected by the blood-brain barrier, consisting of the perivascular feet of astrocytic processes and the nonfenestrated capillary endothelial cells’ tight junctions. The BBB protects neurons and glia from bacterial toxins, infectious agents, and other exogenous substances, and helps maintain the stable composition and constant balance of ions in the interstitial fluid that is required for normal neuronal function.

“PERIPHERAL NERVOUS SYSTEM” • The main components of the peripheral nervous system (PNS) are the nerves, ganglia, and nerve endings. • Nerve fibers (analogous to tracts in the CNS) are bundles of nerve fibers (axons) surrounded (sheathed) by Schwann cells . The sheath may or may not form myelin around the axons, depending on their diameter.

Nerve Organization Axons and Schwann cells are enclosed within layers of connective tissue : 1- Endoneurium is a thin layer, consisting of reticular fibers,, produced mainly by Schwann cells, that surrounds individual nerve fibers. This layer, difficult to observe without specialized stains, contains occasional mast cells and macrophages. 2- Perineurium surrounds each bundle of nerve fibers (fascicle ) . Its inner surface consists of layers of flattened cells joined by tight junctions that prohibit passage of most macromolecules, thus assisting in the formation of the blood-nerve barrier. 3- Epineurium is the layer of dense, irregular fibrous connective tissue (fascia) that forms the external coat of nerve bundles and is often embedded in adipose tissue.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect4 2nd grade

o Ganglia: Ganglia are encapsulated aggregations of neuronal cell bodies (soma) outside the CNS. Their surrounding glial satellite cells supported by delicate connective tissue and surrounded by a denser capsule. Because they serve as relay stations to transmit nerve impulses, at least one nerve enters and another exits from each ganglion. The direction of the nerve impulse determines whether the ganglion will be a sensory or an autonomic ganglion. 1. Autonomic ganglia (motor ganglia) are two-neuron systems with the first neuron named either presynaptic or preganglionic (are located within the central nervous system), and the second nerve cell called postsynaptic or postganglionic (are located in ganglia throughout the body).

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect4 2nd grade

2. Sensory (or craniospinal) ganglia: associated with both cranial nerves (cranial ganglia) and the dorsal roots of the spinal nerves (spinal ganglia). Unlike autonomic ganglia, craniospinal ganglia do not possess synapses. These ganglia contain the cell bodies of sensory neurons, which are pseudounipolar (unipolar) and transmit sensory signals from receptors to the CNS. ✓ Note: The large neuronal cell bodies of ganglia are associated with thin, sheetlike extensions of small glial satellite cells (lab 4)

Spinal ganglion Sympathetic Parasympathetic ganglion gangilon • Satellite cells surrounding • Fewer satellite cells. • Ganglion cells are located each cell body. • Multipolar neurons. within or near the effector • Flattened satellite cells • Nuclei are eccentrically organ. provide structural & located • Usually found between metabolic support. two layers of smooth • Pseudo-unipolar neurons. muscle in the walls of the • Nerve fibers pass through GIT. center of the ganglion and neurons are located peripherally.

Nuclei: Cluster of neuron cell bodies inside White matter (found only in the CNS)

Ganglia: Name for cluster of neuron cell bodies found only in the PNS.

Nerves: One or more bundles of nerve fibers (axons) in the PNS.

Tracts: Another name for a nerve, except this bundle of nerve fibers (axons) in Gray matter (is only found in the CNS).

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect5 2nd grade

Salivary glands

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect5 2nd grade

Salivary acini Serous Mucous Diameter smaller Wider Lumen smaller wider Cell shape pyramidal in shape similar Nucleus Round, basally located Flattened, basally located Myoepitheilal cells + +++ Secretion Watery serous Mucous viscid Example Parotid gland Sublingual gland (mainly mucous , few serous ) Diagram

Serous demilunes are the serous cells at the distal end of mucous tubuloalveolar secretory unit of certain salivary glands. These demilune cells secrete the proteins that contain the enzyme lysozyme, which degrades the cell walls of bacteria. In this way, lysozyme confers antimicrobial activity to mucus.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect5 2nd grade

Salivary Ducts Intercalated ducts → Simple cuboidal epithelium Striated ducts → Simple cuboidal/ low columnar epith. Excretory Intralobular ducts → Simple columnar epith.

Interlobular ducts → Simple columnar epith. Interlobar ducts → Psudostratified epith. Main ducts → Stratified columnar/ seqamous epith.

General histology Digestive system part1 , lect6

Ali Maki

1 Inner surface of the lip= Mucosa Outer surface of the lip= SKIN • thicker, stratified squamous • very thin skin covered by a stratified nonkeratinized oral epithelium. squamous keratinized epithelium. • Beneath the oral epithelium are found • contains hair follicles, sebaceous glands, mucus-secreting labial gland (mixed) and sweat glands. 2 Rudimentary!!

Foliate Papillae:

Filiform Papillae Fungiform Papillae Circumvallate Papillae • are much larger than the fungiform • The most numerous and • Less numerous but larger or filiform papillae, Eight to 12 smallest papillae broader, and taller than the circumvallate papillae • conicalshaped filiform filiform papillae • characterized by deep moats or papillae • more prevalent in the anterior furrows that completely encircle • They cover the entire dorsal region of the tongue. them. surface of the tongue. • Contain taste buds • located in the posterior region of the • No taste buds tongue 3 • taste buds literally Posterior

4 barrel-shaped structures

microvilli exhibit numerous microvilli that Neuroepithelial protrude through the taste pore, (taste) cells closely associated with small afferent nerve fibers . Sustentacular not sensory, supporting function cells

= support the structure and function of Basal cells stem cells, undifferentiated cells the gustatory cells 5 The wall of the digestive tract has four layers Epithelium

Mucosa lamina propria = Loose connective tissue Regulation of peristalsis by: Muscularis mucosae Rugae 1- Submucosal nerve plexus

2- Myenteric nerve plexus Submucosa = Dense irregular connective tissue submucosal nerve plexus

inner circular smooth muscle layers Stomach 3 muscle layers : Muscularis Externa Myenteric nerve plexus oblique, circular, and longitudinal muscle layers outer longitudinal smooth muscle layers

ADVENTITIA Serosa or adventitia SEROSA Thin layer of connective tissue, mesothelium, Thick layer of connective tissue, doesn’t that covers the visceral organs have mesothelium layer

Covers abdominal esophagus, stomach, small Covers thoracic part of esophagus and posterior intestine, and anterior wall of colon wall of ascending and descending colon

6 Structural modifications of the small intestine wall increase surface area

Fold Increase the intestinal surface area

Plicae circulares Submucosa 3-fold

10-fold Villi Lamina propria

Cytoplasm of absorptive cells Microvilli 20-fold

❑ resulting in a total absorptive area of over 200 m2 in the small intestine 7 8 10 cm

10 cm 10 cm 10 cm

9 10 Gastric pits (P)

11 Gastric Glands and Cells

1- Foveolar cell Fundic, cardiac, pyloric Surface mucous cells : Depending on their location Mucous neck cells

2- Chief Cells Fundic only • secrete the inactive enzyme called pepsinogen; pepsinogen is activated to pepsin by: 3- Parietal Cells Fundic only • secrete hydrochloric acid (HCl) which helps convert pepsinogen into pepsin and kills microbes in food • secretes intrinsic factor which helps with absorption of vitamin B12 4- G Cells (Enteroendocrine Cells) Fundic, cardiac, pyloric • secrete several hormones and substances like gastrin, histamine, somatostatin, endorphins

12 Cells of Small Intestine Simple columnar Chyme(FOOD), M.O. 1- Absorptive cells (enterocytes), with microvilli in intestinal epithelium. Secrete diaccaridase and peptidase, lipid absorption Absorption Immunity Goblet cells 2- Goblet cells, interspersed among absorptive cells. They secrete glycoprotein Absorptive cells Paneth cells Microfold cells mucins that are then hydrated to form mucus, whose main function is to protect and lubricate the lining of the intestine. 3- Enteroendocrine cells are scattered throughout the epithelium and intestinal glands 4- Paneth cells produce lysozyme, phospholipase A2, and defensins, all of which bind and break down membranes of microorganisms and bacterial cell walls.

5- Microfold cells are specialized cells that cover the lymphatic Peyer’s patches, M cells selectively endocytose antigens and transport them to the underlying lymphocytes and dendritic cells, which then migrate to lymph nodes for an appropriate immune response. Intestinal villus 13 14 Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect7+8 2nd grade

Pancreas The pancreas is a mixed exocrine-endocrine gland that produces digestive enzymes and hormones. Thin Capsule Thin Trabeculae Fine reticular C.T

It consists of Acini: Serous

Ducts Islets of Langerhans The Exocrine Pancreas • Contains pure serous acini, similar to the parotid gland, highly polarized with spherical nuclei typical protein secreting cells. • Approximately 1.5 L of alkaline pancreatic juice per day and delivers it directly into the duodenum where the HCO3 − ions neutralize the acidic chyme entering there from the stomach and establish the pH for optimal activity of the pancreatic enzymes. • They secrete trypsinogen, chymotrypsinogen, carboxypeptidase, ribo + desoxy nucleases. • Exocrine pancreas is controlled by: → Secretin : fluid and enzyme secretions. → Cholecystokinin:  fluid and  enzyme secretions. Secretin and cholecystokinin are secreted by duodenal Enteroendocrine cells.

Pancreatic ducts 1- Intercalated ducts (made by centro-acinir cells) 2- Intralobular ducts (simple cuboidal epithelium ) 3- Interlobular ducts (simple cuboidal epithelium, simple columnar epithelium) 4- Main pancreatic duct (pesudostratified epithelium) which join the common bile duct, before it open into the ampulla of Vater. ➢ The exocrine pancreas has no stratified ducts.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect7+8 2nd grade

The Endocrine Pancreas “Islets of Langerhans” In humans, the endocrine pancreas consists of about one million of small units called "islets of Langerhans". Each islet consists of small clusters of cells.

• The diameter of the islet ranges from 100 - 200 micrometer. • They are frequently observed in-between the acini of the exocrine pancreas. • Their number is higher in the pancreatic tail. • There are 4 types of cells in each islet called: A (alpha), B (beta), D (delta), and F cells recognized by immunocytochemical methods.

Percentage Position Staining Hormone Function

A 20% peripheral Acidophilic: Glucagon Acts through alpha pink with glycogenolysis and Gomori lipolysis; increases blood glucose content

B 70% Central Basophilic: Insulin cause entry of glucose beta blue with Gomori into cells thus decrease of blood glucose level

D <5% Variable Silver Somatostatin Inhibits the release of delta other hormones from islets

F Rare Variable immunocytochemistry Pancreatic Control the gastric polypeptide secretion and exocrine pancreas

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect7+8 2nd grade

The Pancreas & the Parotid Gland Pancreas Parotid Capsule & Trabcculae thin thick

Duct System few & non stratified well developed & stratified lack striated duct contain striated duct Islets of Langerhans present absent

Centro-acinose cells present absent

Myoepithelial cells absent present

Fat Cells absent present

Liver The liver is a mixed endocrine and exocrine gland, acting as an interface between the digestive system and the blood.

The liver lobule

• Pig liver : The hepatic lobules are clearly • Hepatocytes are arranged in plates or layers 1-2 visible due to the presence of thick layer of cells in thickness, branch and anastomose freely. connective tissues.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect7+8 2nd grade

• It is the basic structural component of the liver, formed by plates of liver cells (hepatocytes). • It is a polygonal mass of tissue, may be surrounded by dense C.T in pigs but not clearly limited in human. • The spaces in-between the plates contain liver sinusoids with fenestrated endothelial cells (sieve plates), to allow exchange of molecules.

• At the corner of hepatic lobule, portal triad is found (in human 3-6/ lobule). • The portal triad contains a branch of hepatic a+ portal v. (big) + bile duct + lymphatic vessel

The Hepatocyte

• Polyhedral cells 20-30 m in diameter, with 1-2 vesicular nuclei and eosinophilic cytoplasm, very rich in mitochondria (2000) and have about 50 Golgi complexes, some sER and rER. • Some nuclei are polyploid with greater size; some have more than 1 or 2 nucleoli. • It stores glycogen which serves to maintain blood sugar. • It shows some lysosomes and peroxisomes in the cytoplasm. • The regenerative capacity of hepatocytes is high. The rat’s liver can regenerate a loss of 75% of its weight in just 1 month. However, in human the process it much restricted.

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect7+8 2nd grade

• Bile canaliculus runs between two hepatocytes, where they show some microvilli. The bile canaliculi end in Hering's canals (simple cuboidal epithelium).

The space of Disse • Hepatocytes are separated from sinusoids by the space of Disse, where it shows some microvilli. • The sinusoids contain some mononuclear phagocytic cells called Kupffer cells. • The space of Disse is supported by fine reticular fibers and contains fat- containing cells called Ito cells, which stores lipid as well as vitamin

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect7+8 2nd grade

Kupffer cells • Kupffer cells, are stellate macrophages found between sinusoidal endothelial cells and on the luminal surface within the sinusoids, mainly near the portal areas. Functions: → break down aged erythrocytes and free heme for re-use → remove bacteria or debris that may enter the portal blood from the gut, → act as antigen-presenting cells in adaptive immunity.

Ito cells Ito cells are found in the space of Disse. They stellate cells with small lipid droplets containing vitamin A. They represent about 8% of the cells in a liver but are difficult to see in routine preparations. Functions: → Store vitamin A → ECM production → Have a regulatory role in local immunity

(cytokine to regulate Kupffer cells )

Functions of the liver ➢ Protein synthesis: albumin, prothrombin, fibrinogen and lipoproteins, about 5% are secreted by Kupffer cells. ➢ Bile secretion: bile acids, phospholipids, cholesterol and bilirubin (90% comes from the intestine and 10% synthesized in the liver). ➢ Metabolite storage: lipids and CHO (triglycerides + glycogen). ➢ Metabolic functions: gluconeogenesis = converting amino acids and lipids → glucose. ➢ Detoxification: oxidation, methylation or conjugation of drugs and toxins (sER). ➢ Kupffer cells metabolize the aged RBCs and hemoglobin. Hepatocytes convert the hydrophobic toxic bilirubin into soluble non-toxic form by glucoronyl- transferase. ➢ Storage of some vitamins (e.g. A & K)

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect7+8 2nd grade

The Gall Bladder

• The gall bladder is a pear shaped organ attached to the lower surface of the liver. It communicates with the hepatic duct through the cystic duct.

Layers of the gall bladder: ➢ Mucosa: is highly folded (especially if empty), lined by simple columnar epith. with microvilli → mucus. ➢ No submucosa ➢ Muscularis externa (Musculosa) is thin, surrounding the gall bladder.

➢ Serosa is typical and lined by peritoneal Section in the gall bladder, stained by H&E. Note the covering. highly folded Mucosa, which is lined with simple columnar epith + microvilli

Dijla University College Assistant lecturer: Ali Maki Hamed Faculty of Dentistry General Histology lect7+8 2nd grade o Pancreatic tissue is protected against autodigestion by the following: 1- Restricting protease activation to the duodenum. 2- Trypsin inhibitor, which is copackaged in the secretory granules with trypsinogen. 3- The low pH in the acini and duct system due to HCO3−secreted by the centroacinar and intercalated duct cells, which helps keep all the enzymes inactive.

o Three ways of considering liver lobule structure?