Histology LC5 Epithelial Tissue PDF 2026

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC5 EPITHELIAL TISSUE COLLEGE OF MEDICINE, BATCH 2026 Transcri...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC5 EPITHELIAL TISSUE COLLEGE OF MEDICINE, BATCH 2026 Transcribers/ Editors: Guzman, A.L., Maligpas, X.E., Dr. Nicanor B. Lacuesta Jr. | Oct. 10, 2022 Matanguihan, N., Nericua, N. EPITHELIAL TISSUE B. FUNCTIONS I. EPITHELIAL TISSUE Protection - Skin protects from sunlight, bacteria and A. ORIGIN physical damage B. FUNCTIONS Absorption - Lining of small intestine, absorbing nutrients II. CHARACTERISTICS OF EPITHELIAL TISSUES III. CLASSIFICATION AND TYPES into blood A. Simple Squamous Epithelium Filtration - Lining of kidney tubules filtering wastes from B. Simple Cuboidal Epithelium blood plasma C. Simple Columnar Epithelium Secretion - Different glands produce perspiration, oil, D. Pseudostratified Epithelium digestive enzymes and mucus E. Stratified Squamous Epithelium F. Transitional Epithelium II. CHARACTERISTICS OF EPITHELIAL TISSUES IV. GLANDS A. Endocrine Glands A. Form continuous sheets (fit like tiles) B. Exocrine Glands B. Avascularity (a=without) - Lacks blood vessels I. EPITHELIAL TISSUE - Nourished by connective tissue C. Regenerate and Repair quickly (but not that quickly) EPITHELIAL TISSUE D. Basement membrane - Underside of all epithelial cells which anchors them - Continuous cells in apposition over a large portion of their to connective tissue surface - Rest on a continuous extracellular matrix - basal lamina - Basal Lamina meshwork of fine filaments - Sheet-like extracellular structure - Forms a boundary layer to control movement of substances - Visible only with electron microscope (20-100 nm from the external environment and internal milieu, or thick) between compartments of the body - Consists of two layers: - Lateral surfaces are highly specialized lamina densa - electron-dense; a delicate network of fine fibrils lamina rarae or laminae lucida - A. ORIGIN electrolucent layers Primary Germ Layers: Ectoderm - gives rise to the corneal epithelium, epidermis of the skin. - Invagination- glandular appendages of the skin, sudiparous, sebaceous, and mammary glands Endoderm - Intestinal glands liver and pancreas - Exocrine glands - Endocrine glands Mesoderm - kidneys and reproductive organs, lining of your blood and lymph vessels, peritoneal cavity and other serous cavities Figure 1. Basal Lamina Layers: Lamina Densa (LD) and Lamina Lucida (LL). All germinal layers can give rise to your epithelial tissues. 1 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. - Extracellular matrix (ECM) components secreted by the epithelial, muscle, adipose and schwann cells: Type IV collagen Laminin Proteoglycan (heparan sulfate) - Attached to the underlying connective tissues by anchoring structures (fibrils) of type VII collagen - May also be closely related to reticular fibers - forms a layer (reticular layer) - produced by connective tissues E. Specialized Lateral surface Intercellular Cohesion - needed for the epithelial cells to be connected to Figure 2. Diagram of the three-dimensional one another view of Zonnula Occludens. - caused by two factors: binding action of the glycoproteins in the plasma membrane and calcium ions - On electron microscope: intercellular junctions (for a more stable connection between cells) - presence of pentalaminar appearance (pentalaminar = 5 layers) Intercellular Junctions - On cryofracture: - Impermeable Junctions:: Zonnulae occludentes - replicas show anastomosing lines of - Adhering Junctions: Zonnulae adherentes, ridges (P face) and grooves (E face) Desmosomes, and Hemidesmosomes - the number of fusion sites or grooves - Communicating Junctions: Gap junctions correlate to the “leakiness” of the epithelium (more grooves, more ridges = 1. Impermeable Junctions more fusion sites = more leak proof) a. Tight or Occluding Junctions - Zonnulae Occludens (plural: zonnulae occludentes) - Forms a band completely encircling the cell and closes off the intercellular space - Major transmembrane proteins: Claudin and Occludin → tight interactions of these two proteins form the seal between two cell membranes - Cytoskeletal components: Actin Filaments - Functions: Figure 3. Electron microscopy of the intercellular junctions: - Functions as tight seal to prevent flow of Zonnula Occludens, Zonnula Adherens and Macula Adherens (Desmosome). materials between cells making the epithelial tissues impermeable (in some epithelia, there is an active electric Zonula occludens tend to be found more apically potential for the transfer of molecules) - separates apical and basolateral membrane domains 2 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. - Functions: - indirectly links to the intermediate filaments of cytokeratin (or tonofilaments) through the desmosomal plaque - its intercellular attachments provide firm cellular adhesion and strength throughout the epithelium Figure 4. View of a tight junction after Cryofracture 2. Adhering Junctions a. Adherens or Anchoring Junctions - Zonnulae Adherens (plural: zonnulae adherentes) - Encircles the cell - distance is greater than the usual 20 nm in these areas - Major transmembrane proteins: Cadherins Figure 5. Electron microscopy of the Desmosome. → binds the cells in the presence of Ca2+ - Cytoskeletal components: Actin Filaments - Functions: - Provides some form of adhesion of one cell to another by the insertion of numerous actin-containing microfilaments into dense plaques on the cytoplasmic surfaces. These microfilaments arise from the web of filaments (terminal web) at the apical pole - together with the zonnulae occludentes, it forms a portion of the apical part of the cell called the terminal bar - makes the apical surface more rigid b. Desmosome Figure 6. Diagram of the three-dimensional view of - Macula adherens Desmosome. - Complex disk-shaped structures on the surface of one cell that matched to another cell - Found in areas where the membranes are c. Hemidesmosomes flattened, very straight in their regions and farther - Morphologically: half a desmosome apart (>30 nm) due to the dense material - Not found in between cells but in the contact intercellular plaques/ attachment plaques points of epithelial cell and the basal lamina - Major transmembrane proteins: Desmogleins - Major transmembrane proteins: Integrins and Desmocollins → bind primarily to laminin molecules in the → bind to the proteins of the dense basal lamina plaques (plakoglobins and desmoplakins) - Cytoskeletal components: Intermediate Filaments 3 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. - are aligned to form a hydrophilic channel between 2 cells for intercellular communications Figure 7. Electron microscopy of the Hemidesmosome. Figure 9. Electron microscopy of the Gap Junction. Figure 8. Diagram of the three-dimensional view of Hemidesmosome. Figure 10. Diagram of the three-dimensional view of Gap Junctions showing the hexamers formed by the Connexins. 3. Communicating Junction F. Apical surface - All epithelial cells gave a top surface that borders a. Gap Junction an open space - known as a lumen - Nexus - Can occur almost anywhere on the lateral Specialization of the Apical Surfaces of Epithelia: surface - Close apposition of cell membranes (2 nm) 1. Microvilli (singular: microvillus) - On cryofracture: aggregates of intermembranous - 1 um long and 0.8 um wide (very small) particles found in circular patches - Few to numerous projections arising from the - Major transmembrane proteins: Connexins apical surfaces of the cell (short or long) for → a polypeptide (MW 26,000 - 30,000 kDa) absorption - Can easily be seen in light microscope → forms hexamers with a central - Has glycocalyx, a filamentous coat of variable hydrophobic pore (Connexon) thickness containing glycoproteins, and is interspersed among the microvilli Connexons - Each microvillus contains a cluster of 20-30 - permeable channels with an average actin-containing microfilaments that are cross- diameter of 1.5 nm linked to each other and to the surrounding 4 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. plasma membrane - basal ends intermingle with the filaments of the terminal web - Densely packed microvilli projecting into the lumen are visible on H&E staining (eosinophilic) as striated or brush border Microplicae - longer folds - can be found in the lining of small intestines and proximal renal tubules Figure 13. Electron microscopy of Cilia 3. Kinocilia - 7-10 um in length and 0.2 um in width - Found on the cells of tissues for special transport of a mucous film or fluid over a surface via rapid oscillations - Rapid oscillations: Effective stroke - rapid stiffening forward (moving the film forward) Recovery stroke - slow relaxation in upward position Figure 11. Microvilli in a light microscope. - Two types of movement: Isochronal stroke - beat together (kinocilia moving together) - “iso” means one. “chrono” means time (one-single timing stroke) Metachronal stroke - successive rows in a sequence (different beatings) - more effective means to transporting fluid over the surface - On electron microscope (EM,) kinocilia have a core complex (axoneme). Axoneme Figure 12. Electron microscopy of microvillus and diagram - two single central microtubules - formed of microvillus showing its interior parts. by 13 protofilaments, similar to those in the cytoplasm - nine doublet peripheral microtubules uniformly spaced around 2. Stereocillia - Subunit A - complete microtubule - Long, non-motile processes of cell (epididymis (13 protofilaments) and hair cells of the inner ear) - Subunit B - incomplete microtubule - resemble microvilli but are longer than them (10 protofilaments) - Parallel to their bases but becomes sinuous (curly) at their tips A radial spoke extends from 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 5 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. Short dynein arms project from - the height and width of the cells of the subunit A to the subunit B of the next epithelium are more or less equal in size doublet - 24 nm intervals ○ Columnar (nuclear near basal layer) - these are elongated cells - columns - the height of the cells of the epithelium is distinctly greater than their width Figure 14. Diagram of axoneme with its parts Figure 16. Classifications of Epithelial Tissue: 4. Flagella For columnar cells, they tend to have nucleus at the basal side of - Internal structure very similar to cilia but longer your epithelium. (15-200 micrometer) According to CELL LAYERS - Not commonly found in the body (only in the free ○ Simple (one layer) swimming spermatozoa) ○ Stratified (many layers) - Has an undulating movement *Named for the type of cell at the apical surface We name the stratified epithelial tissues according to the type of cell that we can find at the apical most portions. Some tissues would have columnar, cuboidal cells at their basal level. Whereas, as they go more superficially to the apical surface, they become flattened so we name them stratified squamous epithelium. TYPES OF EPITHELIUM: A. Simple Squamous Epithelium - Structure: Single layer of flattened cells Figure 15. Sperm cell as a type of flagella. - Function: Absorption and filtration; Not effective protection - single layer of cells - Location: - Walls of capillaries III. CLASSIFICATION AND TYPES - Air sacs in lungs - Lining of the inside of the heart, where it is According to CELL SHAPE called endocardium ○ Squamous - Lining of the blood vessels and lymphatics, - flattened like fish scale where it is called endothelium - their heights being very little as compared - Lining of some parts of the renal tubules, and to their width in some parts of the internal ear ○ Cuboidal - Cubes (more like big and round cells) 6 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. Figure 18. Simple Cuboidal Epithelium. Instead of flat cells, you can see rounded, large cells. C. Simple Columnar Epithelium - also called mucous membranes (when open to body cavities) Figure 17. Simple Squamous Epithelium - Structure: Elongated layer of cells with nuclei at same level B. Simple Cuboidal Epithelium - Special Features: - Structure: Single layer of cube-shaped cells Microvilli: bumpy extension of apical - Function: Secretion and transportation in glands, surface; increase surface area and filtration in kidneys absorption rate - Location: Goblet Cells: single cell gland interspersed among simple columnar epithelium; - Glands and ducts (pancreas & salivary) produce protective mucus particularly in - Kidney tubules the lining of your upper respiratory tract - Ovaries (germinal epithelium) Proteoglycan - Follicles of Thyroid gland - Choroid plexuses - Function: Absorption, Protection & Secretion - Inner surface of the lens - Location: - Pigment cell layer of the retina - Linings of entire digestive tract - Ciliated columnar epithelium lines most of the respiratory tract, the uterus, and the uterine tube - Efferent ductules of the testis - Parts of the middle ear and auditory tube 7 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. Nucleus tends to be found near the basal surface of your cells. Figure 20. Pseudostratified Epithelium All cells are anchored to the basement membrane, but not all of Figure 19. Simple Columnar Epithelium them would reach the apical surface. Those whose nuclei found near the basal lamina tend not to reach the apical surface. D. Pseudostratified Epithelium - Structure: Irregularly shaped cells with nuclei at E. Stratified Squamous Epithelium different levels - Structure: Many layers (usually cuboidal/ - Appear stratified, but aren’t. columnar at the bottom region and squamous at - All cells reach the basement membrane, but not all the top region) of them would reach the apical surface. - Function: Protection- best morphology of epithelial cells for protection - Function: Absorption and Secretion Keratin (protein) is accumulated in older cells near the surface - waterproofs and Goblet cells - produce mucus toughens skin Cilia (larger than microvilli) - sweep mucus - Location: - Location: - Skin (keratinized) - Respiratory Linings & Reproductive tract - Linings of the mouth & throat - Some parts of the auditory tube - Upper respiratory tract - Oral cavity - Portions of gastrointestinal tract 8 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. TYPES: A. Endocrine Glands - No duct, release secretion directly into blood vessels - Often hormones - Examples are thyroid, adrenal and pituitary glands B. Exocrine Glands - Contain ducts, empty onto epithelial surface - Examples are sweat glands, oil glands, salivary glands, and mammary glands  SHAPES OF EXOCRINE GLANDS: Figure 21. Stratified Squamous Epithelium 1. Branching a. Simple - single, unbranched duct b. Compound - branched ducts F. Transitional Epithelium 2. Shape - Structure: Many layers; very specialized (cells at a. Tubular - shaped like a tube base are cuboidal or columnar, at surface will b. Alveolar - shaped like flasks or sacs vary); change between stratified & simple as tissue c. Tubuloalveolar - has both tubes and sacs in gland is stretched out - Function: Allows stretching (change size) - Location: Urinary bladder, ureters & urethra *As transitional epithelium is confined to the urinary tract, it is also called urothelium. Figure 23. Structural Classes of Exocrine Glands Figure 22. Transitional Epithelium  MODES OF SECRETION OF EXOCRINE GLANDS: In contrast to other layers of cells which usually have flattened (How the gland’s product is released) apical surface, here, the apical surface is bumpier and you call this apical cell in your transitional epithelium as umbrella cells. 1. Merocrine - Just released by exocytosis without altering the gland at all - Examples: sweat glands and salivary glands IV. GLANDS 2. Holocrine - One or more cells that make and secrete a product - The gland ruptures and releases secretion and - Secretion consists proteins in aqueous solution (e.g. dead cells hormones, acids, oils, sweat, milk) - Example: Sebaceous glands (oil glands on the face) 9 [HISTOLOGY] 1.05 EPITHELIAL TISSUE – Dr. Nicanor Lacuesta Jr. 3. Apocrine - Product accumulates at the cell’s apical ends, portions of which are then extruded to release the product together with small amounts of cytoplasm and cell membrane. - Example: Mammary glands Figure 24. Mechanism of Exocrine Gland Secretion REFERENCES Mescher, A. L. (2016). Junqueira’s Basic Histology Text and Atlas (Fourteenth Edition). McGraw-Hill Education Dr. Lacuesta’s Powerpoint Presentation. S.Y. 2023-2023.Epithelial Tissue. University of Northern Philippines - College of Medicine 10