FUNCTIONS AND TYPES OF EPITHELIAL TISSUE
Main functions of epithelial tissue:
- line the internal and external surface of many organs and of the whole body, protecting them from mechanical forces and form drying
- act as barriers separating compartments in the body
- form glands that secrete molecules either new, that result from synthesis by the gland cells, or modifications of existing molecules. In some glands (such as when sweat is produced by sweat glands) most of the secretion is simply transported by the cells and no or almost no synthesis is involved.
- transport molecules, particles and ions between the lumen of a cavity and the connective tissue, for example by cells lining blood and lymph vessels and by cells of the digestive tract and renal tubules.
Classification of the epithelial tissue
According to its location in the body, the arrangement and the functions performed by its cells the epithelial tissue is classified into two main types:
Lining (or covering) epithelial tissue
Secretory or glandular epithelial tissue
This classification is however imperfect, as there are many lining epithelia in which some or all cells are also secretory.