This tissue has cells that are clustered tightly. This tissue is avascular which implies that it should get nourishment through the diffusion of the substances from the connective tissue that is underlying via basement membrane. Types of Epithelia in Digestive tract. Epithelium lines up the digestive tube. The epithelium is continuous at skin located at mouth as well as anus. The nature of epithelium changes with body parts. In some parts it works as protective layer and in some other parts it performs the role of absorption.