What function do epithelial tissues primarily serve?

Epithelial tissues primarily serve the essential functions of covering and lining surfaces, protecting underlying structures, and facilitating secretion. They form the outer layer of the skin, line cavities and organs, and make up glands that produce various substances, including sweat, mucus, and hormones. This protective barrier prevents physical damage, pathogens, and dehydration while also aiding in absorption and sensation. The structural arrangement of epithelial cells, which can be simple or stratified and cuboidal, columnar, or squamous, is specifically adapted to fulfill these functions effectively, providing both protection and selective permeability.