Histology LC4: Epithelial Tissue PDF

B. ORIGIN COURSE OUTLINE Primary Germ Layers: I. EPITHELIAL TISSUE Ectoderm – give rise to the corneal epithelium,...

B. ORIGIN COURSE OUTLINE Primary Germ Layers: I. EPITHELIAL TISSUE Ectoderm – give rise to the corneal epithelium, A. Brief overview and epidermis of the skin. B. Origin ○ Invagination – glandular appendages of C. Functions the skin, sudiparous, sebaceous, and D. Characteristics mammary glands. II. CLASSIFICATION OF EPITHELIAL Endoderm – give rise to intestinal glands, liver, TISSUES and pancreas. A. Cell shape and layers ○ Exocrine glands B. Simple squamous epithelium ○ Endocrine glands C. Simple cuboidal epithelium Mesoderm – give rise to kidneys and D. Simple columnar epithelium reproductive organs, lining of your blood and E. Pseudostratified epithelium lymph vessels, peritoneal cavity and other F. Stratified squamous epithelium serous cavities. G. Transitional epithelium H. Glands NOTE: All germinal layers can give rise to epithelial tissues. H.1. Endocrine Glands H.2. Exocrine Glands C. FUNCTIONS H.3. Modes of Secretion III. CHARACTERISTIC FEATURES OF Protection EPITHELIAL CELLS ○ Skin protects from sunlight & bacteria & A. Basal lamina physical damage. B. Intercellular cohesion Absorption E.1. Zonula occludentes ○ Lining of small intestine, absorbing E.2. Zonula Adherens nutrients into blood E.3. Gap Junction Filtration E.4. Desmosome ○ Lining of kidney tubules filtering wastes E.5. Hemidesmosomes from blood plasma IV. SPECIALIZATION OF THE APICAL Secretion SURFACES OF EPITHELIA ○ Different glands produce perspiration, oil, A. Microvilli digestive enzymes and mucus B. Stereocilia C. Kinocilia D. CHARACTERISTICS OF EPITHELIAL D. Flagella TISSUES Form continuous sheets (fit like tiles) Apical surface I. EPITHELIAL TISSUE ○ All epithelial cells have a top surface that borders an open space – known as lumen. Basement membrane A. BRIEF OVERVIEW ○ Underside of all epithelial cells which anchors them to connective tissue EPITHELIAL TISSUE Avascularity (a = without) Are continuous cells in apposition over a large ○ Lacks blood vessels portion of their surface. ○ Nourished by connective tissue Rest on a continuous extracellular matrix – Regenerate and repair quickly. basal lamina – a meshwork of fine filaments. Forms a boundary layer – which controls movement of substances from the external II. CLASSIFICATION OF EPITHELIAL environment and internal milieu, or between TISSUE compartments of the body. Epithelial cells are attached together laterally with highly specialized junctions in order for A. CELL SHAPE AND LAYERS these cells to adhere to each other, and achieve barrier function. Cell shape Lateral surfaces are highly specialized. In order ○ Squamous – flattened like fish scales for them to achieve that barrier function. ○ Cuboidal – cubes ○ Columnar – columns BATCH 2028 1C ANATOMY LC4: EPITHELIAL TISSUE Dr. Lacuesta, N. B. 09/09/2024 Figure 3. Micrograph of kidney glomerulus. (Light Micrograph) The lining of the glomerulus has simple squamous epithelium (Arrow), which shows basophilic flattened cells, large, and robust nuclei. C. SIMPLE CUBOIDAL EPITHELIUM Structure ○ Single layer of cube shaped cells Function ○ Secretion and transportation in glands, filtration in kidneys Location Figure 1. Classifications of Epithelial Tissue ○ Glands and ducts (pancreas & salivary), kidney tubules, covers ovaries How are the tissues differentiated: ○ As seen in Figure 1 - Usually, the nuclei of the squamous epithelium are flattened, which may resemble dark [basophilic] stripes under the light microscope. Cuboidal epithelium would have more rounded nuclei. ○ Discern the cell border - Usually, with cuboidal cells, they have rounded [borders] Figure 4. Micrograph of Islets of Langerhans (Pancreas). and centrally located. Columnar epithelium (Light Micrograph) are elongated, thus the nuclei are also Under light microscopy (100x magnification), islets elongated. Columnar epithelium cells are of langerhans, lining each, are round shaped nuclei usually found at the basement membrane. - simple cuboidal epithelium Cell layers ○ Simple (one layer) ○ Stratified (many layers) ○ Named for the type of cell at the apical surface ○ (Insert pictures) Figure 5. Micrograph of Collecting Duct (Kidney). B. SIMPLE SQUAMOUS EPITHELIUM (Light Micrograph) See the rounded nuclei, with corresponding basal Structure lamina underneath. ○ Single layer of flattened cells Function D. SIMPLE COLUMNAR EPITHELIUM ○ Absorption, and filtration ○ Not effective protection – single layer of Structure cells. ○ Elongate layer of cells with nuclei at same Location level ○ Walls of capillaries, air sacs in lungs Function ○ Form serous membranes in body cavity ○ Absorption, protection & secretion ○ When open to body cavities – called mucous membranes, producing mucus Special Features ○ Microvilli – bumpy extension of apical surface, increase surface area and absorption rate ○ Goblet Cells – single cell glands, produce protective mucus. Figure 2. Micrograph human cheek epithelial cells Location The micrograph exemplifies the squamous cells’ ○ Linings of entire digestive tract fitting against one another like a jigsaw puzzle. BATCH 2028 1C ANATOMY LC4: EPITHELIAL TISSUE Dr. Lacuesta, N. B. 09/09/2024 Figure 6. Micrograph of Gallbladder. (Light Micrograph) Take note that the nuclei in its apical surface should all be found in the same level. Special features of Figure 9. Micrograph of Trachea. (Light Micrograph) these epithelia is that they tend to have apical Under light microscope, the vestibule of glottis, the specializations. For example, microvilli and goblet area where false vocal cords would come in contact cells. with true vocal cords. At a closer look, a lot of nuclei are near the apical surface. Nuclei are not columnar in shape but rather cuboidal, hence called a basal cell — because it's right on the basal membrane and because it can differentiate into any type of cell that needs to be replaced in the respiratory epithelium. May be a columnar epithelium or a goblet cell. So, it's a base cell — a progenitor cell for all the types of cells that are needed. Figure 7. Micrograph of Uterine Gland. (Light Micrograph) A cross section shows the elongated basophilic F. STRATIFIED SQUAMOUS EPITHELIUM nuclei, underlying loose connective tissue and red blood cells found inside the capillaries. Taking a Structure look closer, eosinophilic cytoplasm of each cell. But ○ Many layers (usually cuboidal/columnar at at the apical surface are the basal structures — the bottom and squamous at top) microvilli with a protein or brush border. ○ As they go up, they become flattened. This is the best configuration of cells that will E. PSEUDOSTRATIFIED EPITHELIUM provide maximum protection. Function Structure ○ Protection ○ Irregularly shaped cells with nuclei at ○ Keratin (protein) is accumulated in older different levels - appear stratified, but cells near the surface - waterproofs and aren’t. toughens skin. ○ All cells reach basement membrane Location Function ○ Skin (keratinized), mouth, and throat ○ Absorption and secretion ○ Goblet cells produce mucus G. TRANSITIONAL EPITHELIUM ○ Cilia (larger than microvilli) sweep mucus. Location Structure ○ Respiratory linings and reproductive tract ○ Many layers ○ Very specialized - cells at base are cuboidal or columnar, at surface will vary. ○ Change between stratified and simple as tissue is spread out. Function ○ Allows stretching (change size) Location ○ Urinary bladder, ureters and urethra Figure 8. Micrograph of Male Urethra. (Light Micrograph) The nuclei at the different levels where some would be near the basement surface, others would be near the apical surface — giving the illusion that there are two layers of cells but in actual, rather a single layer. As a general rule, all of the cells in a pseudostratified epithelium should reach the basement membrane but not all will reach the apical surface. BATCH 2028 1C ANATOMY LC4: EPITHELIAL TISSUE Dr. Lacuesta, N. B. 09/09/2024 MODES OF SECRETION ○ Merocrine ○ Just released by exocytosis without altering the gland at all. ○ Example: sweat glands and salivary glands ○ Holocrine ○ The gland ruptures and releases Figure 10. Micrograph of Urinary Bladder. (Light Micrograph) secretion and dead cells as well. ○ Sebaceous (oil glands on the face) A picture of a Transitional epithelium – not only example. stretched. In contrast with other types of epithelium, the apical surfaces are usually flattened. For this White heads and black heads are cellular figure, this transitional epithelium is bumpy. debris that are clogged up in the ducts of oil “Umbrella cells” – Cells at the most apical glands. They are: position. ○ White – if not yet oxidized ○ Black – oxidized H. GLANDS One or more cells that make and secrete a III. CHARACTERISTIC FEATURES OF product. EPITHELIAL CELLS Secretion - protein in aqueous solution: hormones, acids, oils. A. BASAL LAMINA ENDOCRINE GLANDS ○ No duct, release secretion into blood Sheet extracellular structure vessels. Visible only with electron microscope (20-100 ○ Often hormones (e.g estrogen, nm thick) progesterone, testosterone, thyroid Consist of a delicate network of fine fibrils: hormones, oxytocin) lamina rarae or laminae lucida – electron ○ Thyroid, adrenal, and pituitary glands lucent; more diffuse and fibrous lamina densa – electron-dense; a delicate EXOCRINE GLANDS network of fine fibrils ○ Contain ducts, empty onto epithelial Composed of type IV collagen, laminin and surface proteoglycan (heparan sulfate) ○ Sweat, oil glands, salivary glands, and Attached to the underlying connective tissues by mammary glands anchoring structures (fibrils) - type VII collagen ○ SHAPES OF EXOCRINE GLANDS Components of the basal lamina - secreted by ○ Branching the epithelial, muscle, adipose, and Schwann ○ Simple - single, unbranched duct cells ○ Compound - branched May also be closely related to reticular fibers - ○ Shape: either tubular or alveolar forms a layer (reticular layer) - produced by ○ Tubular - shaped like a tube connective tissues ○ Alveolar - shaped like a flasks or sacs ○ Tubualveolar - has both tubes and sacs in gland Figure 11. Electron Micrograph of Basal lamina (BL), Reticular layer (RL), Hemidesmosomes (H). (Transmission Electron Micrograph) B. INTERCELLULAR COHESION Figure 10. Structural Classes of Exocrine Glands Due to the binding action of glycoproteins in the plasma membrane and calcium ions Intercellular junctions: BATCH 2028 1C ANATOMY LC4: EPITHELIAL TISSUE Dr. Lacuesta, N. B. 09/09/2024 ○ Tight junctions (zonulae occludentes) ○ Zonula adherens ○ Gap junction ○ Desmosome (macula adherens) Zonulae Occludentes Tight junctions (singular zonula occludens) Forms a band completely encircling the cell Closes off the intercellular space On electron microscope - pentalaminar Figure 13. Micrograph of Intercellular junctions. (Transmission appearance Electron Micrograph and Illustration) On cryofracture - replicas show anastomosing lines of ridges (P face) and Terminal bar- a combination of zonulae grooves (E face) occludentes and zonula adherens along with the The number of fusion sites or grooves terminal web. correlate to the “leakiness” of the epithelium Functions as a tight seal to prevent flow of Gap Junction materials between cells ○ Nexus - can occur almost anywhere on the In some epithelia there is an electric lateral surface potential - for transfer of molecules ○ Close apposition of cell membranes (2 nm) ○ On cryofracture - aggregates of intramembranous particles found in circular patches ○ Major protein is polypeptide (MW 26,000 - 30,000) ○ Proteins (Connexins) form hexamers with a hydrophobic pore (1.5 nm) - Connexon ○ Connexons are aligned to form a hydrophilic channel between 2 cells - intercellular communications Figure 12. Apical region of Intestinal lining (junctional complex). (Transmission Electron Micrograph) An electron-dense gap in its junctions between the intestinal cells are observed. Zonula Adherens Encircles the cell - distance is greater than the usual 20 nm in these areas Provides some adhesion of one cell to another Provides some adhesion of one cell to another Figure 14. Micrograph of Gap junction viewed from electron microscope. (Transmission Electron Micrograph) Insertion of numerous actin-containing The gap junction can be seen (arrow) as microfilaments into dense plaques on the electron-dense connections between two cells. cytoplasmic surfaces These microfilaments arise from web of Desmosome filaments (terminal web) - provide rigidity to ○ Macula Adherens - complex disk-shaped the terminal apex structure on the surface of one cell - Zonulae occludentes and zonula adherens matched to another cell - terminal bar ○ Membranes are very straight in there regions and father apart (>30 nm) ○ There is dense material intercellular plaques (attachment plaques) - group of intermediate filaments of cytokeratin BATCH 2028 1C ANATOMY LC4: EPITHELIAL TISSUE Dr. Lacuesta, N. B. 09/09/2024 In the small intestine, the microvilli is associated with glycocalyx. Glycocalyx - filamentous coat of variable thickness, contains glycoproteins Light microscope Figure 15. Gap Junction creates gaps that connect animal cells. (Transmission Electron Micrograph) A desmosome (arrow with label) have extending electron-dense adherent plaques in between each Figure 18. Micrograph of microvilli. (Light Micrograph) cells which allows them to link together. The brush border is stained basophilic, due to the presence of glycoproteins. Glycocalyx together with Intermediate filaments (arrow) are seen as the microvilli, these two would make up the brush electron-dense cytoplasmic features. border — all funding to increase the absorptive capacity of intestines. Under a light microscope, it shows simple columnar epithelium. Microvillus - extension - covered by plasma membrane Interiorly - 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 Figure 16. Three -dimensional view of desmosome. (Illustration) terminal web Hemidesmosomes ○ On the contact points of epithelial cell and the basal lamina ○ Morphologically - half a desmosome Figure 19. Micrograph of microfilament. (Illustration) The terminal web is found at the apex part — the terminal bar of each apical cell. And the microvilli and microfilaments intertwine with the terminal apex Figure 17. Hemidesmosome. (Illustration) at a right angle — keeping them upright. Adhering junctions - zonulae adherentes, B. STEREOCILIA hemidesmosomes, and desmosomes Impermeable junctions - zunolae occudentes Communication junctions - gap junctions Long non-motile processes of cell (epididymis and hair cells of the inner ear) Longer than microvilli IV. SPECIALIZATION OF THE APICAL Parallel to their base but become sinuous at SURFACES OF EPITHELIA their tips A. MICROVILLI Few to numerous projections arising from the surface (short or long) Microplicae - longer folds (lining of small intestines and proximal renal tubules) 1 µm high and 0.8 µm wide BATCH 2028 1C ANATOMY LC4: EPITHELIAL TISSUE Dr. Lacuesta, N. B. 09/09/2024 entire length of the kinocilium. Their movement would make the doublets line together at a 24 nm interval. D. FLAGELLA Internal structure very similar to cilia but longer (15 - 200 µm) ○ Not commonly found in the body (only in the free swimming spermatozoa) ○ Has an undulating movement Figure 20. Micrograph of stereocilia C. KINOCILIA Found on the cells for special transport of a mucous film or fluid over a surface Rapid oscillations 7-10 µm in length and 0.2 µm in width Rapidly stiffen forward - effective stroke then more slow relaxation - recovery stroke May beat together (isochronal stroke) or metachronal stroke (successive rows in sequence) On EM - there is a core complex (axoneme) - two single microtubules in the center with nie doublet microtubules uniformly spaced around ○ Central microtubules - 13 protofilaments, similar to those in the cytoplasm Figure 22. Sperm cell. (Illustration) ○ Peripheral microtubules ○ Subunit A - complete microtubule Functions to propel spermatozoa from male toward (13 protofilaments) the female ovum, not by undulating but more of ○ Subunit B - incomplete circular motion. The amount of mitochondria that it microtubule (10 protofilaments) houses in the midpiece is their source of energy and may be completely depleted when they get near the egg cell. References: Mescher, A. L. (2021). Junqueira's basic histology: Text and atlas (17th ed.). McGraw Hill. Dr. Lacuesta’s PowerPoint Presentation. S.Y. 2024-2025 - Epithelial tissue. University of Northern Philippines. College of Medicine Figure 21. Vestibular Hair cell (inner ear). (Illustration) The vestibular hair cell is found in the inner ear. You have one single motile hair, and non motile hair. This would be embedded on a gel containing calcium oxalate crystals. A radial spoke extends forms each subunit - A to the central pair Subunit A of each doublet is connected by fine nexin to the subunit B of the next doublet Nexin maintains the equal spacing between doublets Short dynein arms project from subunit A to the subunit B of the next doublet - 24 nm intervals Dynein does not connect but rather projects. They occur in intervals of the BATCH 2028 1C