Epithelial Tissue

The tissue which covers the body surface, organs, ducts, blood vessels etc. is called an epithelial tissue. The main functions of epithelial tissues are as follows:

1. They help in the exchange of materials from the surrounding environment.
2. They help in the secretion of hormones and other required juices.
3. They help in the absorption of digested food and water in the alimentary canal.

On the basis of form and structure, epithelial tissue is classified into following types:

1. Pavement/Squamous epithelium
2. Cubical epithelium
3. Columnar epithelium
4. Glandular epithelium
5. Ciliated epithelium
6. Stratified epithelium

Pavement/Squamous Epithelium

Squamous epithelium consists of a single layer of cells. The cells of this epithelium are thin, broad and flat which are arranged like the mosaic tiles on the floor. So, it is also called pavement tissue. It is found in the skin epidermis, lining of the mouth, body cavities, oesophagus and blood vessels. It helps in the protection, exchange of gases and ultra-filtration.

Cubical Epithelium

Cubical Epithelium is also a single-layered epithelium tissue. It has equal height and width. It has spherical nucleus placed more or less in the centre. The cells are closely fitted together and lie on a basement membrane. It is found in the duct of sweat gland, liver, seminiferous tubule, uterus etc. It is actively involved in the conduction of secretary materials. It also helps in absorption and excretion.

Columnar Epithelium

Columnar Epithelium is made of the single layer of cells. The cells of this epithelium are elongated and also lie on the basement membrane. The nucleus is usually located at the base of the cell. The height of the cell exceeds its width. It is found in lining of the stomach, intestine, reproductive organs, urogenital organs, gall bladder, salivary gland etc. It main functions are absorption and secretion.

Glandular Epithelium

Glandular Epithelium is a single layered tissue. It is also modified the form of columnar epithelium. The cells of this epithelium are specialized for the secretion of chemical substances needed for different activities of metabolism. Liver, pancreas, mammary glands, sweat glands and mucous glands are the examples of such tissues. These cells secrete the hormone, enzymes, saliva, mucus, etc.

Ciliated Epithelium

Ciliated Epithelium is a single layered tissue. It is modified form of columnar or cubical epithelium. It has fine, hair-like processes called cilia at the free margin. It is found in lining of the uterine tubes, nasal passage and respiratory tract. In the uterine tubes, the cilia propel ova towards the uterus, and in the respiratory tract, it propels mucus towards the throat.

Stratified Epithelium

Stratified Epithelium is formed of many layers of cells. In the deepest layers, the cells are mainly columnar and, as they grow towards the surface they become flattened. The lowest layer is called germinal layer which produces new cells. They are also of different types and are mainly found in the nails, hair and conjunctiva of eyes and larynx. It prevents loss of water and protects from mechanical injury.