Subtopic: Epithelial Tissue

I. Intro­duc­tion

• Epithe­lial tis­sue (epithe­li­um) cov­ers or lines body parts.
• It has a free sur­face exposed to body flu­ids or the exter­nal envi­ron­ment.
• Cells are tight­ly packed with min­i­mal inter­cel­lu­lar matrix.
• II. TYPES OF EPITHELIUM
• A. SIMPLE EPITHELIUM: Sin­gle cell lay­er.
• Func­tions in lin­ing cav­i­ties, ducts, and tubes.
• Sub­types- based on cell shape:
• 1. Squa­mous: Thin, flat­tened cells with irreg­u­lar bor­ders.
• Loca­tion: Blood ves­sel walls, lung air sacs.
• * Func­tion: Dif­fu­sion bound­ary.
• 2. Cuboidal: Cube-like cells.
• Loca­tion: Gland ducts, kid­ney tubules (nephrons).
• Func­tion: Secre­tion and absorp­tion. Often has microvil­li (e.g., PCT of nephron).
• 3. Colum­nar: Tall, slen­der cells with basal­ly locat­ed nuclei.
• Loca­tion: Stom­ach and intesti­nal lin­ing.
• Func­tion: Secre­tion and absorp­tion.
• 4. Cil­i­at­ed: Colum­nar or cuboidal cells with cil­ia.
• Loca­tion: Bron­chi­oles, fal­lop­i­an tubes.
• Func­tion: Move­ment of par­ti­cles or mucus.
• B. COMPOUND EPITHELIUM: Two or more cell lay­ers; pri­mar­i­ly pro­tec­tive.
• Lim­it­ed role in secre­tion and absorp­tion.
• Loca­tion: Skin (dry sur­face), buc­cal cav­i­ty, phar­ynx, sali­vary and pan­cre­at­ic duct lin­ings.
• III. GLANDULAR EPITHELIUM: Spe­cial­ized for secre­tion.
• Types:Uni­cel­lu­lar :- Iso­lat­ed glan­du­lar cells (e.g., gob­let cells in the ali­men­ta­ry canal).
• Mul­ti­cel­lu­lar: Clus­ters of cells (e.g., sali­vary glands).
• Gland Clas­si­fi­ca­tion by Secre­tion Release:
• Exocrine: Secrete prod­ucts (mucus, sali­va, ear­wax, oil, milk, diges­tive enzymes) through ducts or tubes.
• Endocrine: Duct­less glands; secrete hor­mones direct­ly into sur­round­ing flu­id.