Epithelial tissue extends throughout the body. They form the covering of all body surfaces, linear body cavities, and hollow organs, and are the main tissue of the glands. They perform various functions, including protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception, it meanly creates protective boundaries and is involved in the diffusion of ions and molecules.
There are different types of epithelial tissue depending on their function in a particular location. The simplest classification of these tissues is based on the number of cell layers.