Epithelial tissue is the covering tissue. It covers most organs and cavities within the body. It also forms a barrier to keep different body system separate. Epithelial tissue are tightly packed and forms a continuous sheet. They don’t have any intercellular spaces only a small amount of cementing material is present between them. The skin, the lining of the mouth, the lining of blood vessels and kidney tubule all are made of epithelial tissue. Obviously anything entering or leaving must have to cross at least one layer of epithelial tissue. As a result permeability of epithelia plays an important role in exchanging of material. On the basis of their structure and function different types of epithelial tissues are present.
Squamous epithelial cell: This are extremely thin and flat and form a delicate lining. The oesophagus, lining of the mouth are covered by it. the skin which protects the body is also made of squamous epithelial.
Cuboidal epithelium: It is a cube shaped epithelial cell which forms the lining of kidney tubules and ducts of salivary glands in order to provide them mechanical strength.
Columnar epithelium: This are tall epithelial cells which are present in the inner lining of the intestine. They have a hair like projection on their outer surfaces called as cilia. These cilia can move and their movement pushes the mucus forward to clear it.