HISTOLOGY - THE EPITHELIAL TISSUE LESSON FOR COLLEGE

For college students undertaking any course in medical field

1. EPITHELIAL TISSUE MARK LESTER B CAUAN, RMT

2. 4 BASIC TISSUE TYPES Epithelial Connective Muscular Nervous

3. FUNCTIONS Covering, lining, and protecting surfaces (epidermis) Absorption (the intestinal lining) Secretion (parenchymal cells of glands)

4. CHARACTERISTIC FEATURES OF EPITHELIAL CELLS Tall columnar to cuboidal to low squamous cells Epithelial cell nuclei – vary in shape Columnar cells – elongated nuclei Cuboidal – spherical nuclei Squamous – flattened nuclei Lamina Propria – connective tissue that underlies the epithelia lining the organs of the digestive, respiratory, and urinary systems

5. Basement Membrane thin extracellular, felt-like sheet of macromolecules where the basal surface of all epithelia rests A semipermeable filter for substances reaching epithelial cells from below Basal lamina Reticular lamina

6. Basement Membrane

7. Intercellular Adhesion and Other Junctions

8. SPECIALIZATIONS OF THE APICAL CELL SURFACE Microvilli visible as a brush or striated border projecting into the lumen about 1 μm long and 0.1 μm wide, but with hundreds or thousands present on the end of each absorptive cell, the total surface area can be increased by 20- or 30-fold contains bundled actin filaments capped and bound to the surrounding plasma membrane by actin-binding proteins

9. SPECIALIZATIONS OF THE APICAL CELL SURFACE Stereocilia much less common type of apical process best seen on the absorptive epithelial cells lining the male reproductive system Increase the cell’s surface area facilitating absorption Inner ear sensory cells

10. SPECIALIZATIONS OF THE APICAL CELL SURFACE Cilia long, highly motile apical structures, larger than microvilli, and containing internal arrays of microtubules not microfilaments abundant on cuboidal or columnar cells of many epithelia 5-10 μm long and 0.2 μm in diameter, which is much longer and two times wider than a typical microvillus exhibit rapid beating patterns that move a current of fluid and suspended matter in one direction along the epithelium

11. TYPES OF EPITHELIA

12. Covering Epithelia

13. Simple Squamous Epithelium

14. Simple Cuboidal Epithelium

15. Simple Columnar Epithelium

16. Secretory Epithelia and Glands Secretory cells may synthesize, store, and release proteins, lipids, or complexes of carbohydrates and proteins Unicellular glands – these are scattered secretory cells which are common in simple cuboidal, simple columnar, and pseudostratified epithelia Goblet cell Exocrine glands – remain connected with the surface epithelium; epithelia of exocrine glands are organized as a continuous system of many small secretory portions and ducts that transport the secretion out of the glan d Endocrine glands – lose the connection to their original epithelium and therefore lack ducts

17. Secretory Epithelia and Glands

18. Secretory Epithelia and Glands

19. TRANSPORT ACROSS EPITHELIA Many cells have the ability to actively transport certain ions against concentration and electrical potential gradients Transcellular transport – some epithelial cells specialize in the transfer of ions and water in either direction across the epithelium Cells of the proximal renal tubules are specialized structurally for transcellular transport The apical surface at the tubule lumen is freely permeable to Na+ the basolateral cell membranes have sodium pumps for the active extrusion of Na+ into the interstitial fluid outside the tubules Osmotic and electrical balance is maintained by the passive transfer of chloride ions (Cl−) and water into the cell All cells can also internalize extracellular molecules and fluid using endocytosis and formation of cytoplasmic, membrane-bound vesicles

20. RENEWAL OF EPITHELIAL CELLS Epithelial tissues are relatively labile structures whose cells are renewed continuously by mitotic activity and stem cell populations. The rate of renewal varies widely In stratified epithelial tissues, stem cells and mitosis occur only within the basal layer in contact with the basal lamina Epithelia are normally capable of rapid repair and replacement of apoptotic or damaged cells

21. THANK YOU!