Epithelial Tissue

Epithelia are linings that can be classified as simple or compound. They have a basement membrane, nerve supply, but no blood supply. Epithelia are exposed to friction, allowing for growth and repair. During sleep, cells appear regular, geometric, with obvious nuclei.

Simple epithelial cells:

• Squamous: Very flat with a central nucleus; thin and delicate. Functions in diffusion or osmosis. Found in lung alveoli, blood capillaries, and Bowman’s capsule in kidneys.

• Cuboidal: Line ducts and tubes to allow material passage. Located in kidney tubules, sweat ducts, and glands like thyroid and breast tissue.

• Columnar: Taller with a slightly ovoid nucleus; may be ciliated. Has goblet cells producing mucus. Found in respiratory tract, trachea, bronchi, alimentary tract, and small intestine.

Compound epithelium:

• Contains a basal layer on the basement membrane that actively divides and pushes older cells upwards. Typically pink and includes mucous membranes found in the vagina, mouth, tongue, and oesophagus.

The skin:

• The outer layer of epithelium, which has a layer of dead cells (epidermis) that become keratinised (cornified) as they advance. Keratin serves to prevent microorganisms from entering lower layers and provides waterproofing.