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Epithelium and Glands

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Epithelium and Glands EPITHELIUM AND GLANDS DR. ASHA SHIRAHATTI ASSISTANT PROFESSOR DEPARTMENT OF ANATOMY USM-KLE IMP SCHEME OF PRESENTATION • Characteristic features and functions of epithelial tissues • Classification of epithelial tissues • Surface modifications of epithelial tissue • Junctional complexes of epithelial tissue • Characteristic features and functions of glandular tissue • Classification of glandular tissue • Mode of secretion of glandular tissue Tissues • groups of cells that are similar in structure and function Epithelium • Coverings • Linings of surfaces Connective • Support • Bone, ligaments, fat Muscle • Movement Nervous • Control • Brain, nerves, spinal cord CHARACTERISTICS OF EPITHELIAL TISSUE • Cells rests on basement membrane • Avascular tissue. • Supported by connective tissue • Innervated • Highly regenerative CHARACTERISTICS OF EPITHELIAL TISSUE (cont) • Epithelium form continuous cellular sheet • Cells are closely packed together by specialized contacts known as cell junctions • Cells are extremely cohesive and relatively strong force is necessary to separate them. • It invaginates into underlying connective tissue, specializing as glands FUNCTIONS • Protection - Skin protects from sunlight & bacteria & physical damage. • Absorption - Lining of small intestine, absorbing nutrients into blood • Filtration - Lining of Kidney tubules filtering wastes from blood plasma • Secretion - Different glands produce perspiration, oil, digestive enzymes and mucus • Sensation - to receive and transduce external stimuli as taste buds of tongue, olfactory epithelium of nasal mucosa and retina of eye • Transportation - transport of materials or cells along the surface of an epithelium by mobile cilia or transport of materials across epithelium to and fro from connective tissue • Lubrication - Glands secreting mucus CLASSIFICATION OF EPITHELIUM • Cell Shape 1. Squamous – flattened like fish scales 2. Cuboidal - cubes 3. Columnar – columns • Cell Layers 1. Simple (one layer) 2. Stratified (many layers) SIMPLE SQUAMOUS EPITHELIUM • Location • walls of blood vessels & • Single Layer of lymphatic ENDOTHELIUM flattened cells • Form serous membranes in body cavity e.g. pleura, • pericardium, peritoneum Function MESOTHELIUM • Absorption and filtration • • Not effective Lines inside of heart protection – single ENDOCARDIUM layer of cells. • Air sacs in lungs MESOTHELIUM SIMPLE SQUAMOUS EPITHELIUM SIMPLE CUBOIDAL EPITHELIUM • Single layer of cube shaped cells Function • Secretion and transportation in glands, absorption in kidneys Location • Thyroid follicle, kidney tubules, covers ovaries SIMPLE COLUMNAR • ElongatedEPITHELIUM layer of cells with nuclei at same level Function • Absorption & Secretion • When open to body cavities – called mucous membranes SIMPLE COLUMNAR EPITHELIUM • Special Features Microvilli Cilia Goblet cells,(single cell glands, produce protective mucus). Surface modifications of epithelial tissue • MICROVILLI • CILIA • STEREOCILIA Microvilli • (eg.) in small intestine • Finger-like extensions of the plasma membrane of apical epithelial cell • Increase surface area for absorption • Nonmotile • Temporary or permanent • 1 µm : height • 0.8 µm : width • Terminal web : supports microvilli • composed of actin filaments, fimbrin & villin Microvilli • STRIATED BORDER : microvilli arranged regularly • Long microvilli arranged parallel to each other • Ex – small intestine • BRUSH BORDER– not arranged regularly • Ex- gall bladder, PCT of kidney CILIA • Hair-like, motile extensions • Moves mucus, etc. over epithelial surface 1-way • Core contains central 2 & peripheral 9 micotubules • 5-10 µm : length • 0.2 µm : diameter • Shaft – free part • Base – attached part • FUNCTIONS OF CILIA • MOVES MUCOS, FLUID or small solid particle in a specific direction. • Helps to move ova through the uterine tube & spermatozoa through male genital tract • Olfactory cilia – nonmotile – sensory in function - smell STEREOCILIA • Very long thick microvilli • Seen on receptor cells in the internal ear ( signal generation) STEREOCILIA • Seen on the epithelium of epididymis ( absorption) PSEUDOSTRATIFIED EPITHELIUM • Cells are of different heights with nuclei at different levels – appear stratified, but aren’t. • All cells rest on basement membrane, but all cells don't reach the surface • Function PSEUDOSTRATIFIED • Movement and Secretion EPITHELIUM • Goblet cells produce mucus • Location • Cilia (larger than • Trachea & bronchial tree microvilli) sweep mucus STRATIFIED SQUAMOUS EPITHELIUM • Many layers, stronger than simple • On dry surface becomes keratinised • On wet surface becomes nonkeratinized • Function • Protection • Keratin (protein) is accumulated in older cells near the surface – waterproofs and toughens skin. • Location • Skin (keratinized), esophagus, vagina STRATIFIED CUBOIDAL EPITHELIUM • Sweat gland ducts • Large ducts of exocrine glands STRATIFIED COLUMNAR EPITHELIUM • Anorectal junction • Some part of male urethra UROTHELIUM/TRANSITIONAL • Many layers EPITHELIUM • Very specialized – cells at base are cuboidal or columnar; at surface are umbrella shaped. • cells are capable of stretching & covered by glycoprotein • Cells are firmly connected by desmosomes. Bcz of these connctions cells retained their position when epithelium is stretched or relaxed. FUNCTIONS • Effective barrier –glycoprotein - prevent absorption of toxic substance in urine • Allows stretching (change size) • Location • Urinary bladder & urethra UROTHELIUM/TRANSITIONAL EPITHELIUM UROTHELIUM/TRANSITIONAL EPITHELIUM BASEMENT MEMBRANE • Formed by = basal lamina • Resting membrane (glycoprotein)+ reticular • Provides adhesion to cells lamina • Contains type IV collagen FUNCTIONS OF BASEMENT MEMBRANE • Provide support to epithelium • Act as mechanical barrier • Provides selective filtration barrier JUNCTIONAL COMPLEXES • Plasma membranes of 2 adjacent cells are separated from each other by gap. This gap is occupied by specialized structures called junctional complexes. 1. Occluding Junctions (zona occludens): joins cell together; seals to prevent loss of material 2. Zonula adherens 3. Macula adherens Gap Junctions : for communication ZONULA OCCLUDENS • At apical part of the cell • “Tight” junctions • Belt or band-like structure that encircles the entire circumference • Sealing effect: preventing passage of materials through intercellular space from lumen • Occludin, claudins ZONULA ADHERENS • Below zonula occludens • Provides adhesion of one cell to its neighbors by a gap, 20nm • Plasma membrane of cell thicked bcz of presence of proteins on inner surface • Thicked areas are held by fibrills • Cadherins, integrins: transmembrane protein DESMOSOMES • Found along the lateral cell membrane • Plasma membrane of cell thicked bcz of presence of proteins on inner surface • Cells are separated by a gap of 30nm & bridged by transmembrane proteins • Thicked areas are held by fibrills • Helps to resist shearing forces HEMIDESMOSOMES • Resembles half- desmosomes • Bind the cell to the BL • Contains integrins GLANDS • One or more cells that make and secrete a product. • Secretion FUNCTION OF THE GLANDS • 1.Hormones Eg.Thyroxine, Insulin • 2.Enzymes Eg.trypsinogen, amylase • 3.Excretion Eg.excess of water and salt GLANDS • Exocrine glands • Contain ducts, empty onto epithelial surface • Sweat, Oil glands, Salivary glands, Mammary glands • Endocrine glands • No duct, release secretion into blood vessels • hormones • Thyroid, adrenal and pituitary glands • Endocrine glands two types • 1.Cord and clump type • 2.Follicular type 1.CORD AND CLUMP TYPE • Cells arranged in irregular cords and clumps • Secretion stored- intracellular method • Secretion- directly delivered outwards • Ex – adrenal gland FOLLICULAR TYPE • Cells arranged circular • Secretion stored extracellular • Eg. Thyroid follicle CLASSIFICATION OF EXOCRINE • Exocrine glands classifiedGLANDS on six points • 1.Number of cells • 2.Shape of secretary portion [not gland] • • 3.Duct pattern • 4.Manner of secretion • 5.Nature of secretion • 6.Development EXOCRINE GLANDS CLASSIFICATION (CONTD). • According to number of cells • 1. Unicellular eg. goblet cell • 2. Multicellular eg. parotid gland ACCORDING TO SHAPE OF SECRETORY PORTION 1. Acinar - flask like 2. Alveolar - rounded 3. Tubular - straight or coiled Eg- sweat glands ACCORDING TO BRANCHING OF DUCT • 1. Simple glands- single duct • eg. Tubular glands of stomach wall • 2. Complex glands- branched duct • eg. Parotid gland ACCORDING TO MODE OF SECRETION • 1.Holocrine-cells disintegrate and die Eg. Sebaceous glands in skin • 2.Apocrine-luminal part disintegrates leaving nuclei and basal portion. Cell regenerates Eg. Apocrine sweat glands, mammary glands • 3.Merocrine (Epicrine / Eccrine)-cell membrane intact Eg. pancreas ACCORDING TO NATURE OF SECRETION • 1.Mucus glands eg. Sublingual salivary gland ,Goblet cells • 2.Serous glands eg. parotid salivary gland, exocrine of pancreas • 3.Mixed glands - eg. Submandibular salivary gland CLASSIFICATION ACCORDING TO DEVELOPMENT • Ectodermal – glands of skin, mammary gland , lacrimal gland, salivary gland • Mesodermal – suprarenal cortex, gonads, kidney • Endodermal – thyroid, parathyroid , thymus, liver. MTF •Regarding epithelium and glands F A Stratified epithelium contains single layer of cells F B nuclei at same levels in pseudostratified epithelium T C Sebaceous glands are Holocrine glands F D Exocrine glands are ductless glands T E Goblet cell is a unicellular gland SEQ • Describe epithelium under following headings. • 1. Classify epithelium with examples • 2. Draw transitional epithelium and label it .
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