Glands like the pancreas are largely composed of specialised epithelia. Epithelia have a number of important characters. Epithelia are made up of cells bound together by cell junctions of different kinds, depending on the function of the epithelium. They may also be joined by special structures on the surface of the cell, known as cell junctions. There are three types of cell junctions, tight junctions, desmosomes and gap junctions.
Tight junctions consist of a partial fusion of the lipid membranes of two adjoining cells.
Desmosomes are much stronger and more complex, and include CAMs and proteoglycans, as well as a structure called a dense area within the cell. There are two sorts, button desmosomes and belt desmosomes. These junctions can resist stretching and twisting. Gap junctions are not intended to provide strength. They are made up of interlocking membrane proteins called connexons.