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MHSB EPITHELIAL TISSUES W4 T2 DRA. CHONA ARAGA Septembe...

MHSB EPITHELIAL TISSUES W4 T2 DRA. CHONA ARAGA September 5, 2017 Lecture, Audio, Book – box, Keypoints – Broken box SURFACE/ MEMBRANE EPITHELIUM I. INTRODUCTION TO EPITHELIAL TISSUE - continuous sheet of closely adherent cells covering A. Simple epithelium- a type of epithelium lined by body surface single layer of cells. Can be furthermore subdivided - Forms boundary layer that controls movement of according to the shape of the cells substances between external and internal environment or between internal compartments a.1. Simple squamous epithelium- lined with single - May be specialized for absorption, secretion or ion layer of flattened or squamous cells transport - for easier diffusion of substances that will be - Lower most cells rest on continuous, thin supporting passing the epithelium layer called basal lamina Examples: mesothelium, endothelium of small - Composed of closely aggregated polyhedral cells with strong blood vessels, parietal layer of the Bowman’s adhesion to one another and attached to thin layer of extracellular capsule, pulmonary alveoli matrix - Basal lamina - Attached to underlying connective tissue via anchoring fibrils (type VII collagen) - Acts as selective filter - Acts as scaffolding when regenerating cells - Only in EM - Composed of type IV collagen, laminin and enactin a.2. Simple cuboidal epithelium- lined by a single o Laminin- glycoproteins that self- assemble as a layer of cuboidal cells lacelike network below basal pole of cells - for secretion and absorption o Enactin/ nidogen, perlecan- holds laminin and type IV glycogen together Examples: thyroid follicles, germinal epithelium of - Reticular lamina- reticular fibers associated with ovaries, distal convoluted tubules of the kindey the basal lamina CHARACTERISTIC OF EPITHELIAL TISSUES a. cells are closely adherent with each other b. cells are arranged in layers or sheets c. avascular- no space for blood vessel, receive nourishment only via diffusion d. the cells rest on the basal lamina e. they are continuously renewed and replaced a.3. Simple columnar epithelium- lined by single f. metaplastic- when subject to prolonger irritation, it layer of columnar cells may transform to a different type that is better - functions for absorption suited to resist irritant Examples: cells lining the GIT, gall bladder Principal functions of epithelial tissues: a.4. Simple columnar ciliated epithelium- lined by  Covering, lining and protecting surface (eg. Epidermis) single layer of columnar cells provided with cilia  Absorption (eg. Intestinal lining) Examples: uterus, fallopian tube  Secretion (eg. Parenchymal cells of glands II. CLASSIFICATION OF EPITHELIAL TISSUES  Surface or Membrane epithelium- form surface coverings and lining membranes  Glandular epithelium- epithelium of glands Transcribed by: Jamie Dianne Dionio Checked by: Page 1 of 6 MHSB W4T2 EPITHELIAL TISSUES W4T2 B. Pseudostratified epithelium- a type of epithelium c.2. Stratified cuboidal epithelium- a type of lined by single layer of columnar cells, but the epithelium lined by several layers of cells, and the nucleus is located at different levels, thus giving an upper most layer is formed of cuboidal cells impression of layering or stratification - absorptive- secretory function Example: pars nervosa of male urethra, ducts of b.1. Pseudostratified ciliated epithelium- a type of sweat glands and sebaceous glands epithelial cells provided with cilia Example: cells lining upper respiratory tract, c.3. Stratified columnar epithelium- type of trachea, bronchi epithelium lined by several layers of cells and the uppermost layer of cells is formed of columnar cells b.2. Pseudostratified non- ciliated epithelium- the Example: penile urethra, ducts of salivary glands, cells do not have cilia ducts of mammary glands Example: seminal vesicles, ejaculatory ducts, epididymis D. Transitional epithelium/urothelium- type of epithelium lined by several layers of cells. The C. Stratified epithelium- a type of epithelium lined by number of cells layers may vary as well as shape of several layers of cells. Depending on the shape of cells depending on the functional state of the the upper right layers of the cell. organ, whether they are relaxed or empty, full or distended. c.1. Stratified squamous epithelium- type of Examples: ureter, urinary bladder, renal calyces epithelium lined by several layers of cells and the uppermost layer is formed of flattened or squamous cells. Depending whether the uppermost layer of flattened cells is formed of living or dead cells, this type can be subdivided into further subtypes. c.1.1 stratified squamous non keratinized epithelium- a type of epithelium lined by several layers of cells and the uppermost layer of flattened cells is formed of living cells. Examples: esophagus, vagina, oral mucosa c.1.2. stratified squamous keratinized epithelium- a type of epithelium lined by several GLANDULAR EPITHELIUM layers of cells and the uppermost layer of I. According to number of cells that make up the flattened cells is formed of dead cells gland - membrane specialization: keratin a. Unicellular-made up of a single cell Examples: epidermis of the skin, hard palate, - Common in simple cuboidal, simple columnar and gingivae pseudostratified epithelia Example: goblet cell Transcribed by: Jamie Dianne Dionio Checked by: Page 2 of 6 MHSB W4T2 EPITHELIAL TISSUES W4T2 b. Multicellular- many cells make up a gland a. Exocrine- pour their secretions through Example: salivary glands, sebaceous glands duct system - Retain their connection with surface epithelium II. According to type of secretion b. Endocrine- directly pour their secretion in a. Purely serous- thin, watery secretion the blood Example: parotid glands, von Ebner’s gland - Lose connection to original epithelium b. Purely mucous- thick viscid secretion Example: goblet cells V. According to structure of multicellular exocrine c. Muco-serous (mixed) glands Example: submandibular glands a. Tubular (predominantly serous), sublingual glands i. Simple tubular- intestinal crypts of (predominantly mucus) Lieberkhun d. Cytogenic ii. Simple coiled tubular- eccrine sweat Example: testis and ovary glands of the skin iii. Simple branched tubular- fundic glands of the stomach iv. Compound tubular- liver, testis b. Alveolar/ acinar/ saccular i. Simple alveolar- sebaceous glands ii. Simple branched alveolar- sebaceous glands iii. Compound alveolar- mammary gland Serous Mucous c. Tubulo-acinar/ mixed/ racemose i. Compound tubulo-acinar- salivary glands III. According to mode of secretion a. Merocrine- secretory products exit the glands by exocytosis without loss of cytoplasm or III. CELL COHESION membrane - Dependent on cell adhesion molecules like cadherin Example: eccrine sweat glands, pancreatic - Cells are attached by local specializations called acinus junctional complexes b. Apocrine- secretory products exit the cell with some cytoplasm and membrane, hence, with FORMS OF JUNCTIONAL COMPLEXES partial destruction of cells Example: mammary glands, apocrine sweat glands of the axillary areas and groin areas c. Holocrine- exocytosis of the secretory product is followed by lysis of the cell, hence, total destruction Example: skin’s sebaceous gland IV. According to presence or absence of ducts Transcribed by: Jamie Dianne Dionio Checked by: Page 3 of 6 MHSB W4T2 EPITHELIAL TISSUES W4T2 1. Zonula occludens stresses without becoming - Most apical part of the cell separated from the basal lamina - Tight junction, occluding junction o basal lamina- extracellular layer found - Belt- like specialization that encircles columnar cells beneath all epithelia below the free surface of the epithelium  lamina lucida- a transparent layer - Constitute selective permeable barrier between adjacent the epithelium and is apical and basolateral plasma membrane which composed of large proteogy=lycan prevent substances from crossing the epithelium and collagen type IV - Occluding- protein at sites of apparent fusion of  lamina densa- meshwork of fine opposing membranes filaments of collagen type VII - Form a seal between adjacent cells looping around collagen type I - Claudin and occluding- responsible for seal between membrane IV. SPECIALIZATIONS OF THE APICAL CELL SURFACE A. Microvilli 2. Zonula adherens - array of projections that are functions for absorption - Intermediate junction, fascia adherens - also functions to increase absorptive surface - Encircles apical portion below the occludens - brush border- kidney - Cross- links are made possible by myosin, α-actinin - striated border- GIT, small intestine and vinculin - sterocilia- epididymis - Stabilizes epithelium by connecting the terminal - glycocalyx- covers intestinal microvilli which aids for digestion webs of adjoining cells of certain molecules - Cell- to-cell adherence - Sites of string cell adhesion - Immediately below zonula occludens - Cadherin- mediates cell adhesion by interacting with Ca 2+ - Catenin- binds cadherin to actin filaments 3. Macula adherens - Desmosome - Small, round specialization on the sides of adjoining B. Cilia cells - Functions to facilitate movement of substances - Trans-membrane linkers bind membranes and - Long projecting structures containing internal array of microtubules dense plaques together - Primary cilium- non-motile but enriched with receptors and - Cell to cell attachment signal transduction complexes for light, odor, motion and flow of - Contribute to the stability of the epithelial by fluid. linking the cytoskeleton of adjoining cells - Motile cilia- abundant in apical domains of many cuboidal and - Plakoglobin and desmoplakin- anchoring proteins that columnar cells bind intermediate filaments to cytoplasmic side of cell - Axoneme- nine doublets form an array around two central membrane microtubules (9+2 assembly) - Kinesin and dynein- for transport of molecular components into and out of the organs 4. Nexus - Gap junction/ communicating junction - Cell to cell communication - Connexons- circular patch on each side of the membrane - permits passage of ions and small molecules from cell to cell - present in electrically active tissue - Found not only in epithelium but also in smooth and striated muscles REFERENCES - Channels for communication between adjacent cells Dr. Chona Araga’s lecture o Hemidesmosomes- anchor basal cells to Junquiera’s Basic Histology Text and Atlas the basal lamina Di Fiore’s Atlas of Histology with Functional Correlations  found only in stratified epithelium to withstand blows and shearing Transcribed by: Jamie Dianne Dionio Checked by: Page 4 of 6 MHSB W4T2 EPITHELIAL TISSUES W4T2 Transcribed by: Jamie Dianne Dionio Checked by: Page 5 of 6 MHSB W4T2 EPITHELIAL TISSUES W4T2 Transcribed by: Jamie Dianne Dionio Checked by: Page 6 of 6