Epithelial Cells

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Epithelial cells are a group of tightly compressed cells that layers itself on the internal and external surfaces of bodily organs and other surfaces found in the body, these cells are collectively also referred to as a tissue called epithelium[1].

These cells function as the layer which separates the inside of the body from the outside environment. They are necessary as different environments are made from various compositions, and the mixing of them can cause many problems. Epithelial cells can be found in the intestine, skin, lungs and kidney amongst other things.

Epithelial membranes are classified as either cutaneous (relating to the skin), mucous, or serous. Mucous membranes, which line all cavities that are open the external environment, include the digestive and respiratory tract. Serous membranes, which are not open to the external environment, line the abdominal and thoracic cavities[2].

Epithelial cells make up the cellular layer, known as the Epithelium or Epithelial tissue, that coats the external surface of a structure or covers a cavity. This layer is often used to seperate body tissue from the external environment it's found in:

  1. Skin
  2. Intestine
  3. Lungs
  4. Kidney

Classification

The epithelial cells can be categorised with regards to their shape: flat, which are known as squamous; roughly cubed, or cuboidal; and finally the taller ones are known as columnar. The epithelium they form can be made up of one or more layers of these cells, which are classified as simple or stratified, respectively[3].

Properties & Structure

There are two sides to an epithelial cell, the apical membrane which is usually exposed to the extracellular fluid in the lumen and the basal membrane which is secured to another cell.

Cilia are often found on the apical membrane and these significantly increase surface area to aid absorption, and even in some organs are used as a brush border to prevent infection.

In a layer of epithelium, there are junctions between each cell known as 'tight' or 'leaky' junctions. The tight junctions limit small molecules or ions moving laterally, creating and upholding membrane domains.

References

  1. Wisegeek what are epithelial cells http://www.wisegeek.com/what-are-epithelial-cells.htm last accessed 04/12/2015
  2. eHow,what are the functions of epithelial cells? http://www.ehow.com/facts_5553002_functions-epithelial-cells.html last accessed 04/12/2015
  3. Fry, M. Page, E. (2008) Catch up Biology, 3rd Edition, Banbury: Scion Publishing Ltd.
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