FUNCTIONS AND CLASSIFICATION OF EPITHELIAL TISSUE
Main functions of epithelial tissue:
- lining surfaces
- secreting molecules or ions
- transporting molecules or ions between two separate compartments
Important features of the surface coating function:
- to provide mechanical protection to the coated surface
- to function as a barrier separating compartments in the body
- to absorb molecules, transporting them from one compartment to another
- to provide protection for some surfaces such as by preventing them from drying out.
The secretion and transport functions consist fundamentally of
- gathering small molecules and use them to synthesize larger molecules (macromolecules) that will be secreted by the cells.
- to transform molecules by adding, removing or replacing their components and secreting them.
- in some cases (such as when sweat is produced by sweat glands) most of the secretion is simply transported by the cells and no or almost no sytnthesis is involved.
- transport of 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 TISSUEL
According to its location, the arrangement of its cells andof its functions, the epithelial tissue is classified into two main types:
LINING 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.