Epithelial Cells

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.

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 boarder 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.