The epithelial tissue forms the covering or lining of most of the organs. The cells of epithelial tissue are tightly packed and form a continuous sheet. There is small amount of cementing materials between the cells and no intercellular space is present. Permeability of the epithelial tissue plays a great role in exchange of materials among various organs it also plays an important role in osmoregulation. All epithelial tissues are separated by the underlying tissue by an extracellular fibrous basement membrane.
Epithelial tissues are of following types:
Simple Epithelium
Cuboidal Epithelium
Columnar Epithelium
Stratified Epithelium
1. Simple Epithelium
The simple epithelium is composed of a single layer of cells. This type of epithelial tissue forms the lining of blood vessels and alveoli. Thin layer of cells facilitates exchange of substances; in such cases.
2. Cuboidal Epithelium
The cells are cube-shaped in cuboidal epithelium. Linings of kidney tubules and ducts of salivary glands are composed of cuboidal epithelium. Cuboidal cells provide mechanical support. Cells of epithelium may play the role of secretion and then they are called glandular epithelium.
3. Columnar Epithelium
Cells are column-shaped in columnar epithelium. Columnar epithelium facilitates secretion and absorption. For example; the lining of intestine is composed of columnar epithelium. In some organs, columnar epithelium has cilia present on the outer surface. Cilia facilitate movements of certain substances. The ciliated epithelium in the respiratory tract pushes the mucus forward.
4. Stratified Epithelium
Cells of the stratified epithelium are in many layers. Skin is an example of stratified epithelium. Stratification of layers prevents wear and tear.
