Epithelial Tissues (002) PDF

(002) EPITHELIAL TISSUES DR. LACUESTA | 10/01/2020 3. Filtration: Lining of Kidney tubules filtering...

(002) EPITHELIAL TISSUES DR. LACUESTA | 10/01/2020 3. Filtration: Lining of Kidney tubules filtering wastes from blood plasma OUTLINE I. EPITHELIAL TISSUE 4. Secretion: Different glands produce A. Origin perspiration, oil, digestive enzymes and B. Functions mucus C. Characteristics D. Classifications C. CHARACTERISTICS II. GLANDS Form continuous sheets (fit like tiles) A. Types of Glands 1. Apical Surface B. Modes of Secretion a. Topmost surface of epithelial tissue III. BASAL LAMINA IV. INTERCELLULAR COHESION b. All epithelial cells have a top surface A. Tight junctions (Zonnulae Occludentes) that borders an open space – known B. Zonula Adherens as a lumen (e.g. lumen of blood C. Gap junction vessels) D. Desmosome (Macula Adherens) 2. Basement Membrane E. Hemidesmosomes a. Basal surface of epithelial tissue V. SPECIALIZATION OF APICAL SURFACES OF b. Underside of all epithelial cells EPITHELIA which anchors them to connective A. Microvilli tissue B. Stereocillia 3. Avascularity (a = without) C. Cillia a. Lacks blood vessels D. Flagella b. Nourished by connective tissue 4. Regenerate & repair quickly I. EPITHELIAL TISSUES D. CLASSIFICATIONS Named for the type of cell at the apical surface. Continuous cells in apposition over a large portion of their 1. Cell Shape surface a. Squamous –flattened like fish scales; Rest on a continuous extracellular matrix – basal lamina – flattened nucleus; little to no surrounding meshwork of fine filaments cytoplasm; their heights being very little -Forms a boundary layer – control movement of as compared to their width. substances from the external environment and internal milieu, or b. Cuboidal – cubes; round nucleus at the between compartments of the body center of cell with a lot of surrounding -Lateral surfaces are highly specialized cytoplasm; the height and width of the cells of the epithelium are more or less A. ORIGIN: PRIMARY GERM CELLS equal in size. 1. Ectoderm - gives rise to the corneal epithelium, c. Columnar – columns; elongated nucleus epidermis of the skin. found near the basal surface of the cell Invagination – glandular appendages of leaving a lot of space for cytoplasm at the the skin, sudiparous, sebaceous, and apical surface of the cell; the height of the mammary glands cells of the epithelium is distinctly greater 2. Endoderm – intestinal glands liver and pancreas than their width a. Exocrine glands 2. Cell Layers b. Endocrine glands a. Simple (one layer) 3. Mesoderm – kidneys and reproductive organs, b. Stratified (many layers) lining of your blood and lymph vessels, peritoneal cavity and other serous cavities SIMPLE SQUAMOUS EPITHELIUM B. FUNCTIONS 1. Protection: Skin protects from sunlight & Structure bacteria & physical damage. - Single Layer of flattened cells Function 2. Absorption: Lining of small intestine, - Absorption, and filtration absorbing nutrients into blood PREPARED AND EDITED BY: Lacasandile, D., Lajara, P., Lamsis, V., Laniog, T., Natividad, J., Navarro, A., Navalta, C., Inferitis K.  (002) EPITHELIAL TISSUES DR. LACUESTA | 10/01/2020 - Not effective protection – single layer of cells. SIMPLE COLUMNAR Structure - Elongated layer of cells with nuclei at same level - "picket fence" appearance Location Function - Walls of capillaries, air sacs in lungs - Absorption, Protection & Secretion - Form serous membranes in body cavity - When open to body cavities – called mucous - Lines the inside of the heart, where it is membranes called endocardium; and of blood vessels Special Features and lymphatics, where it is called - Microvilli, bumpy extension of apical surface, increase endothelium. surface area and absorption rate - Lines some parts of the renal tubules, and in - Goblet cells, single cell glands, produce protective some parts of the internal ear mucus Location Bowman’s capsule - Linings of entire digestive tract - Ciliated columnar epithelium lines most of the respiratory tract, the uterus, and the uterine tube - It is also seen in the efferent ductules of the testis, parts of the middle ear and auditory tube - Ependyma lining the central canal of the spinal cord and the ventricles of the brain SIMPLE CUBOIDAL EPITHELIUM Structure - Single layer of cube shaped cells Function - Secretion and transportation in glands, filtration in kidneys Location - Glands and ducts (pancreas & salivary), kidney tubules, covers ovaries (germinal epithelium) PSEUDOSTRATIFIED EPITHELIUM - Follicles of Thyroid gland - Choroid plexuses Structure - Inner surface of the lens, and the pigment cell layer of the - Irregularly shaped cells with nuclei at different levels – retina appear stratified, but aren’t. - All cells reach basement membrane PREPARED AND EDITED BY: Lacasandile, D., Lajara, P., Lamsis, V., Laniog, T., Natividad, J., Navarro, A., Navalta, C., Inferitis K.  (002) EPITHELIAL TISSUES DR. LACUESTA | 10/01/2020 - Not all cells reach the apical surface Location Function - Urinary bladder, ureters & urethra - Absorption and Secretion - Goblet cells produce mucus *cells at the topmost layer are called umbrella cells, because it - Cilia (larger than microvilli) sweep mucus resembles an open umbrella Location *As transitional epithelium is confined to the urinary tract it is also - Respiratory Linings & Reproductive tract called urothelium - Some parts of the auditory tube. STRATIFIED SQUAMOUS EPITHELIUM II. GLANDS Structure - Many layers (usually cubodial/columnar at bottom and squamous at top) One or more cells that make and secrete a product. - Best morphology for protection Secretion = protein in aqueous solution: hormones, acids, oils Function A. Endocrine glands - Protection No duct, release secretion into blood vessels - Keratin (protein) is accumulated in older cells near the - Often hormones surface – waterproofs and toughens skin. - Thyroid, adrenal and pituitary glands Location B. Exocrine glands - Skin (keratinized), mouth & throat (non-keratinized squamous epithelium) TRANSITIONAL EPITHELIUM Structure - Many layers Contain ducts, empty onto epithelial surface - Very specialized – cells at base are cuboidal or - Sweat, Oil glands, Salivary glands, Mammary columnar, at surface will vary glands - Change between stratified & simple as tissue is - Branching stretched out - Simple – single, unbranched duct Function- - Compound – branched. - Allows stretching (change size) Shape: tubular or alveolar PREPARED AND EDITED BY: Lacasandile, D., Lajara, P., Lamsis, V., Laniog, T., Natividad, J., Navarro, A., Navalta, C., Inferitis K.  (002) EPITHELIAL TISSUES DR. LACUESTA | 10/01/2020 Tubular – shaped like a tube - Alveolar – shaped like flasks or sacs - Tubuloalveolar – has both tubes and sacs in - gland C. Modes of Secretion 1. Merocrine - Just released by exocytosis without altering the gland at all. Ex: Sweat glands and salivary glands 2. Holocrine - The gland ruptures and releases secretion and dead cells as well. - Sebaceous (oil glands on the face) only example White heads – cellular debris IV. INTERCELLULAR COHESION Black heads – oxidize Due to the binding action of glycoproteins in the III. BASAL LAMINA plasma membrane and calcium ions (weak covalent bond) Sheetlike extracellular structure Intercellular junctions: Visible only with electron microscope (20-100 nm thick) i. Tight junctions (zonnulae occludentes) Consists of a delicate network of fine fibrils – lamina densa ii. Zonula adherens Electrolucent layers on both sides – lamina rarae or lamina iii. Gap junction lucida iv. Desmosome (macula adherens) Composed of type IV collagen, laminin and proteoglycan v. Hemidesmosomes (heparan sulfate) o type IV collagen: Monomers of type IV collagen self A. Zonnulae Occludentes assemble into a two-dimensional network of evenly Tight junctions (singular zonnulae occludens) spaced subunits Forms a band completely encircling the cell o laminin: large glycoproteins that attach to Closes off the intercellular space transmembrane proteins called integrins at the cells’ On electron microscope – pentalaminar basal surface and project through the network of type appearance IV collagen On cryofracture – replicas show anastomosing o Nidogen and perlecan: Respectively a short, rod-like lines of ridges (P face) and grooves (E face) protein and a proteoglycan, both of these cross-link The number of fusion sites or grooves correlate to laminins to the collagen network and help determine the “leakiness” of the epithelium the porosity of the basal lamina and the size of More fusion sites, less permeable epithelium molecules able to filter through it. Functions as a tight seal to prevent flow of materials between cells Attached to the underlying connective tissues by anchoring The seal between the two cell membranes is due structures (fibrils) – type VII collagen to tight interactions between the transmembrane Components of the basal lamina – secreted by the epithelial, proteins claudin and occludin muscle, adipose, and Schwann cells In some epithelia there is an electric potential – May also be closely related to reticular fibers – forms a layer for transfer of molecules (reticular layer) – produced by connective tissues Basement membrane vs Basal lamina -basal lamina: denotes the fine extracellular layer seen ultrastructurally -basement membrane: entire structure beneath the epithelial cells visible with the light microscope PREPARED AND EDITED BY: Lacasandile, D., Lajara, P., Lamsis, V., Laniog, T., Natividad, J., Navarro, A., Navalta, C., Inferitis K.  (002) EPITHELIAL TISSUES DR. LACUESTA | 10/01/2020 Nexus- can occur in almost anywhare on the lateral surface Mediate intercellular communication rather than adhesion or occlusion between cells. Close apposition of cell membrane (2 nm) On cryofracture- aggregates of intermembranous particles found in circular patches Major protein is polypeptide (MW 26,000-30,000) Proteins (Connexins) form hexamers with hydrophobic pore (1.5 nm)- Connexon Connexons- aligned to form hydrophilic channel between 2 cells- intercellular communication ( a channel or gap by which substances would pass from one cell to another) B. Zonula Adherens Encircles the cell – distance is greater than the usual 20 nm in these areas Provides some adhesion of one cell to another Insertion of numerous actin-containing microfilaments into dense plaques on the cytoplasmic surfaces These microfilaments arise from web of filaments (terminal web) – provide rigidity to the terminal apex Cell adhesion is mediated by cadherins, D. Desmosomes transmembrane glycoproteins of each cell that bind each Macula adherens - complex disk-shaped structure on other in the presence of Ca2+ the surface of one cell matched to another cell Membranes are very straight in the regions and farther apart (30nm) There is dense material intercellular plaques (attachment plaques)- group of intermediate filaments of cytokeratin E. Hemidesmosomes On the contact points of epithelial cells and the basal lamina Zonnulae occludentes and zonula adherens – terminal bar Morphologically- half a desmosomes Forms rigidity Unlike desmosomes the clustered transmembrane Seals off the apical surface of epithelium proteins that indirectly link to cytokeratin intermediate filaments are integrins rather than cadherins C. Gap Juntion PREPARED AND EDITED BY: Lacasandile, D., Lajara, P., Lamsis, V., Laniog, T., Natividad, J., Navarro, A., Navalta, C., Inferitis K.  (002) EPITHELIAL TISSUES DR. LACUESTA | 10/01/2020 Adhering junctions- zonullae adherentes, hemidesmosomes, and Rapidly stiffen forward- effective stroke then more slow desmosomes relaxation- recovery stroke May beat together (isochronal stoke) or metachronal Impermeable junctions- zonullae occludentes stroke (successive rows in sequence) Metachronal stroke – more effective; inside the Communicating junctions- gap junctions respiratory system On EM- there is a core complex (axoneme) 2 single microtubules in the center with 9 V. SPECIALIZATION OF APICAL doublets microtubules uniformly spaced around Central microtubules - 13 protofilaments, similar SURFACES OF EPITHELIA to those in the cytoplasm Peripheral microtubules A. Microvilli Subunit A - complete microtubules (13 protofilaments) Few to numerous projections arising from surface (short Subunit B - incomplete microtubules (10 protofilaments) or long) A radial spoke extends from each subunit -A to the Microplicae- longer folds (lining of short intestines and central pair proximal renal tubules) Subunit A of each doublet is connected by fine nexin to 1 um high and 0.8 um wide the subunit B of the next doublet Glycocalyx- filamentous coat of variable thickness, Short dynein arm project from subunit A to the subunit contains glycoprotein B of the next doublet - 24 nm intervals Facilitate the dissolving of substances for absorption Speeds up absorption Microvillus- extension- covered by plasma membrane Inferiorly- cluster of 20-30 actin-containing microfilaments that are cross-linked to each other and to the surrounding plasma membrane- basal ends intermingle with the filaments of the terminal web Small intestine lining- densely packed microvilli are visible as a brush or striated border projecting into the lumen D. Flagella Flagella - internal structure very similar to cilia but longer (15 - 200 um) Not commonly found in the body (only in the free- swimming spermatozoa) Has an undulating movement B. Stereocillia TEST YOUR KNOWLEDGE Long non-motile processes of cell (epidydimis and hair Name the followign tissues: cells of the inner cell Longer that microvilli 1. Parallel to their base but becomes sinous at their tips (or curly at their tips) increase the cells’ surface area, facilitating absorption C. Kinocillia Found on the cells for special transport of a mucous film or fluid over a surface Rapid oscillations 7-10 um in length and 0.2 im in width PREPARED AND EDITED BY: Lacasandile, D., Lajara, P., Lamsis, V., Laniog, T., Natividad, J., Navarro, A., Navalta, C., Inferitis K.  (002) EPITHELIAL TISSUES DR. LACUESTA | 10/01/2020 2. REFERENCES Mesher, A (2016). Junqueira’s Basic Histology Text and Atlas. McGraw-Hill Education. 3. 4. 5. Answers: 1.Simple Squamous epithelium 2. Simple Cuboidal Epithelium 3. Pseudostratified Columnar Epithelium 4. Stratified Squamous Epithelium 5. Transitional epithelium PREPARED AND EDITED BY: Lacasandile, D., Lajara, P., Lamsis, V., Laniog, T., Natividad, J., Navarro, A., Navalta, C., Inferitis K.