Epithelium: Specialized Surfaces Linings

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Epithelia are layers of single or multiple cells that cover the exterior surface of our bodies. These cells, known collectively as Epithelium, line the interior surfaces, comprise the secretory portions of glands and ducts, and are also found in the sensory reception regions of certain organs like our ears and nose.

Epithelia serve a valuable role in regulating the absorption, secretion, excretion, sensory perception, and, in some cases, the contraction of the tissues in which they are found. Simply put; our many Epithelium serves to help regulate our interaction with the environment and many exchanges that occur within our bodies.


Collectively, epithelia are referred to as epithelium. These tissues are found throughout the body, serve a wide range of roles, and have been observed in many different forms, some of which are listed below:

Squamous – Comprised of flat almost globular collections of cells that are permeable and located where small molecules pass quickly. These are located in areas where fast exchanges take place such as the lungs, blood vessels, and lymph tissues (1).

Cuboidal – named for the shape of the cell when observed perpendicularly, these cube-shaped cells can be found in glands, ducts, and the liver. These cells carry secretions and are often contain microvilli along their borders (2).

Columnar – Elongated shapes with cylindrical shapes whose function involves continual secretions. These cells are common among the uterus, stomach, and small intestinal lining (2).

Simple, Stratified, Pseudostratefied, and Transitional Epithelia

Simple epithelium is comprised of a single-layer cell structure attached to the bottom membrane of the surfaces on which they are located. Simple epithelia are primarily located in areas where secretion, absorption, and filtration occur–such as the epithelial lining of the gastrointestinal tract.

A stratified epithelium consists of multiple cell layers of which are attached only via the bottommost (basal) layer of epithelia. Pseudostratified epithelium appears to have multiple cell layers but, in fact, are all attached to the basal layer making them a functionally simple arrangement.

The transitional epithelium contains multiple layers of irregularly shaped cells that are common among the bladder, ureters, and other organs where tissue is required to be elastic and flexible (2).


  1. Ober, William, et al. Human Physiology: An Integrated Approach. 2nd ed., Prentice-Hall, 2001.
  2. Bostwick Taylor, Patty, and Wingerd, Bruce. The Human Body: Concepts of Anatomy and Physiology. N.P., Jones & Bartlett, 2020.