Cell junctions are the specialized connections between the plasma membranes of adjoining cells. The three general types of cell junctions are as follows: tight junctions that bind cells together, forming a barrier that is leakproof; for example, they form the lining of the digestive tract, preventing the contents of the intestine from entering the body; anchoring (or adhering) junctions link cells together, allowing them to function as a unit and form tissue, such as in the heart muscle; and communicating (or gap) junctions that allow rapid chemical and electrical communication between cells.