48. Covering epithelia. Simple epithelium – types

2 types

Epithelial tissue can be broadly classified into two main groups based on the number of cell layers:

1. Simple Epithelium: Contains a single layer of cells.

2. Stratified Epithelium: Contains two or more layers of cells.

Simple Squamous Epithelium:

• Structure: Composed of a single layer of flat and thin cells with a prominent, protruding nucleus (the thickest part of the cell).

• Location: Found lining blood and lymphatic vessels (endothelium), and body cavities such as the pleural cavity (mesothelium in the lungs).

• Functions:

  • In blood and lymphatic vessels, it serves a covering function and facilitates the passage of materials via diffusion and filtration.

  • In the lungs, it allows for the exchange of gases.

Simple Cuboidal Epithelium:

• Structure: Consists of a single layer of cube-shaped cells with spherical nuclei; cells are about as wide as they are tall.

• Location: Found in ducts of glands, the surface of ovaries, kidney tubules, and the thyroid gland.

• Functions:

  • Provides a covering for ducts of exocrine glands and the surface of the ovary.

  • In kidney tubules, it is involved in the absorption of metabolites.

  • In the thyroid gland, it plays a role in secretion.

Simple Columnar Epithelium:

• Structure: Made up of a single layer of tall, column-like cells with oval-shaped nuclei that are usually located at the base of the cells.

• Location:

  • Ciliated Types: Found in the bronchi, uterine tubes, and uterus.

  • Non-ciliated Types: Found in the digestive tract (lining of the stomach and intestines) and bladder.

• Functions:

  • Provides a protective covering in certain ducts of exocrine glands.

  • In the digestive tract, it absorbs nutrients from digested food.

  • In the stomach, large intestine, and uterus, it aids in secretion to protect the epithelium.

  • The ciliated type helps facilitate the movement of particles or gametes (e.g., in the Fallopian tubes).

Pseudostratified Columnar Epithelium:

• Structure: Appears to be stratified (layered), but is actually a single layer of cells of varying heights; all cells rest on the basement membrane. The cells are tall and irregularly shaped, with nuclei at different levels, giving the illusion of multiple layers.

• Location:

  • Ciliated Types: Found in the respiratory tract (e.g., trachea and bronchi), where they often contain cilia.

  • Non-ciliated Types: Found in ducts of some exocrine glands and the epididymis, where they may contain stereocilia.

• Functions:

  • Non-ciliated: Provides a covering function in ducts of certain exocrine glands.

  • Ciliated: In the respiratory tract, cilia help move mucus and trapped particles out of the airways. In the epididymis, stereocilia assist in the absorption and maturation of sperm.