How is the epithelium suited for the substances ?

Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another. Epithelial layers are avascular, but innervated.

Epithelial cells have two surfaces that differ in both structure and function.

The epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue. One side of the epithelial cell is oriented towards the surface of the tissue, body cavity, or external environment and the other surface is joined to a basement membrane. The basement layer is non-cellular in nature and helps to cement the epithelial tissue to the underlying structures.