Human Anatomy
Epithelium Histology
Epithelium histology for MBBS: classification by layers and shape, functional correlation, surface specialisations and cell junctions, mapped to NMC codes AN65.1 and AN65.2.
MedNext Academy | 3 min read
Epithelium Histology
Epithelium histology for MBBS: classification by layers and shape, functional correlation, surface specialisations and cell junctions, mapped to NMC codes AN65.1 and AN65.2.
This chapter classifies epithelia by layering and cell shape and links each type to its function and location. It also covers the surface specialisations and cell junctions that define epithelial tissue.
High-yield: Epithelium Histology
- Epithelium is a cellular tissue that covers surfaces, lines cavities and forms glands, resting on a basement membrane.
- Epithelia are classified by the number of cell layers and the shape of the surface cells.
- Simple squamous epithelium suits diffusion and lines alveoli, the loops of Henle and the lining of blood vessels as endothelium.
- Simple cuboidal epithelium lines kidney tubules, ducts and the surface of the ovary.
- Simple columnar epithelium lines the stomach and intestines and may bear a brush border of microvilli.
- Pseudostratified ciliated columnar epithelium lines the trachea and much of the respiratory tract.
- Stratified squamous epithelium protects surfaces and is keratinised in the skin and non-keratinised in the oesophagus and mouth.
- Transitional epithelium or urothelium lines the urinary tract and stretches as the bladder fills.
- Microvilli increase the absorptive surface, cilia move material along, and stereocilia are long microvilli of the epididymis.
- Epithelial cells are joined by tight junctions, adherens junctions, desmosomes and gap junctions.
- Tight junctions seal the intercellular space and control paracellular movement near the apical surface.
- Desmosomes provide strong mechanical adhesion and are numerous in the epidermis.
- Gap junctions allow ions and small molecules to pass directly between adjacent cells.
- Hemidesmosomes anchor the basal cells to the underlying basement membrane.
- Epithelia are avascular and receive nutrition by diffusion from the underlying connective tissue.
Epithelial types and where they are found
- **Simple squamous:** Diffusion and filtration. Alveoli, endothelium of vessels, mesothelium of serous cavities.
- **Simple columnar:** Absorption and secretion. Stomach and intestine; may carry a microvillous brush border.
- **Pseudostratified ciliated columnar:** Trachea and respiratory tract; cilia sweep mucus upward.
- **Transitional (urothelium):** Urinary tract. Stretches and flattens as the bladder distends.
NMC competencies in this chapter
- **AN65.1:** Identification and functional correlation of the types of epithelium
- **AN65.2:** Ultrastructure of epithelium
Frequently Asked Questions
How is epithelium classified?
By the number of cell layers, giving simple or stratified epithelium, and by the shape of the surface cells, giving squamous, cuboidal or columnar. Special types include pseudostratified and transitional epithelium.
What lines the urinary bladder?
Transitional epithelium, also called urothelium. Its cells change shape as the bladder fills and empties, appearing dome-shaped when relaxed and flattened when stretched.
What are the main epithelial cell junctions?
Tight junctions that seal the space, adherens junctions and desmosomes that provide adhesion, gap junctions that allow communication, and hemidesmosomes that anchor cells to the basement membrane.
Why does epithelium need an underlying connective tissue?
Epithelium is avascular, so it depends on diffusion from the vascular connective tissue beneath the basement membrane for its nutrition and oxygen.
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