Cells of the epithelium are set very close to each other, separated by very thin films of extracellular material. Neighbouring cells are held together by cell junctions. The epithelial tissue rests on a non-cellular Basement Membrane, which separates it from the underlying connecting tissue.

The basement membrane is a non-cellular membrane made up of two layers.

Upper thin layer called as basal lamina made up of glycol-proteins and muco-polysaccharides secreted by epithelial cells.

Lower thick fibrous layer also called as Reticular lamina, made up of reticular fibers and collagen fibers which are the part of underlying connective tissue.

Blood vessels are absent in the epithelial tissue. Materials are exchanged between epithelial cells and vessels of the connective tissues by diffusion across the basement membrane. The epithelial tissue is classified into simple and compound epithelia.