Epithelium_Histology_Presentation by Dr.Rumaisa PT

THIS slide contains all the basic knowledge of epithelium regarding histology covering all the types of epithelium and visual representation of histology images simple squamous stratified etc all types are covered

1. Epithelium General Histology – By Laiq Hussain Siddiqui Presented by: Dr.Rumaisa PT

2. Introduction Epithelium: sheet of closely packed cells covering surfaces & lining cavities Functions: protection, absorption, secretion, sensation, excretion Derived from all three germ layers: ectoderm, endoderm, mesoderm

3. General Characteristics Cells closely packed, minimal intercellular material Rest on basement membrane Avascular – nutrients via diffusion Cells show polarity (apical, lateral, basal surfaces) High regenerative capacity

4. Basement Membrane Thin extracellular supportive layer Components: Basal lamina (lucida + densa) + Reticular lamina Functions: support, selective barrier, regulates cell growth

5. Cell Junctions Tight junctions (occludens): prevent leakage Adherens junctions: adhesion between cells Desmosomes: strong intercellular attachment Gap junctions: communication channels Hemidesmosomes: anchor to basement membrane

6. Classification of Epithelium Based on number of layers : Simple, Stratified Based on shape: Squamous, Cuboidal, Columnar Types : Simple, Stratified, Pseudostratified , Transitional

7. Simple Epithelium Single layer of cells, all on basement membrane Types: Simple squamous, Simple cuboidal, Simple columnar, Pseudostratified columnar

8. Simple Squamous Epithelium Flat, thin cells ('tile-like') Location: alveoli, endothelium (vessels), mesothelium (serous membranes) Function: diffusion, filtration, lubrication

9. Simple Cuboidal Epithelium Cube-shaped cells, round nuclei Location: kidney tubules, thyroid follicles, gland ducts Function: secretion & absorption

10. Simple Columnar Epithelium Tall cells with oval nuclei Location: intestine, gall bladder, uterine tubes Specializations: microvilli, cilia, goblet cells Function: absorption, secretion, transport

11. Pseudostratified Columnar Epithelium Appears stratified, but all touch basement membrane Usually ciliated with goblet cells Location: respiratory tract (trachea, bronchi) Function: protection, mucus secretion & clearance

12. Stratified Epithelium Multiple layers, only basal cells touch basement membrane Provides protection Types: Stratified squamous (keratinized, non-keratinized), Stratified cuboidal, Stratified columnar

13. Stratified Squamous Epithelium Keratinized: epidermis – protection against stress Non-keratinized: oral cavity, esophagus, vagina Function: protection from abrasion & infection

14. Stratified Cuboidal & Columnar Stratified cuboidal: ducts of sweat & salivary glands – protection & secretion Stratified columnar: male urethra, conjunctiva – protection & secretion

15. Transitional Epithelium Specialized stratified epithelium Dome-shaped superficial cells change shape (distensible) Location: urinary bladder, ureter, renal pelvis Function: protection, stretch & recoil

16. Surface Specializations Microvilli: increase absorption (intestine – brush border) Cilia: move mucus/fluids (respiratory tract, uterine tube) Stereocilia: long microvilli for absorption/sensation (epididymis, inner ear)

17. Polarity of Epithelial Cells Definition: Polarity refers to the functional and structural orientation of epithelial cells, with distinct domains. Domains: Apical Surface: Faces lumen or external environment. Specializations: microvilli , cilia , stereocilia . Functions: absorption, secretion, movement. Lateral Surface: Faces neighboring cells. Contains cell junctions (tight junctions, adherens junctions, desmosomes, gap junctions). Functions: adhesion, communication, barrier function. Basal Surface: Rests on basement membrane . Contains hemidesmosomes and basal infoldings . Functions: attachment, exchange of molecules, anchorage.

18. Polarity of Epithelial Cells Importance of Polarity: Maintains directionality of secretion and absorption. Essential for tissue integrity and function. Loss of polarity is a hallmark of malignancy .

19. Functions of Epithelium Protection: skin, mucosa Absorption: intestine, kidney Secretion: glands Excretion: renal tubules Sensation: taste buds, olfactory epithelium Transport: ciliary movement

20. Clinical Correlations Carcinomas: malignant epithelial tumors Metaplasia: replacement of one epithelium by another (smoker’s airway) Ciliary dysfunction: Kartagener syndrome – infertility, infections Basement membrane thickening: diabetes, hypertension

21. Summary Epithelium = protective & functional covering tissue Classified into simple, stratified, pseudostratified, transitional Functions: protection, absorption, secretion, sensation, transport Structural modifications support specialized roles

22. References Laiq Hussain Siddiqui – General Histology Junqueira’s Basic Histology Gartner & Hiatt – Color Textbook of Histology