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