Cell junctions are specialized protein structures that allow cells to attach, communicate and exchange materials with each other. They are critical for maintaining tissues and organs, as well as regulating cell behavior. There are several types of cell junctions, each with its own unique structure, function and location.

1. Tight junctions: Tight junctions form a barrier between adjacent cells, preventing the passage of fluids and molecules between them. They are found in epithelial cells lining organs and tissues such as the intestine, bladder, and skin.

2. Adherens junctions: Adherens junctions connect cells through the interaction of the transmembrane protein cadherin, which binds to nearby cadherins on adjacent cells. They are important for maintaining tissue integrity and regulating cell behavior.

3. Desmosomes: Desmosomes anchor adjacent cells together through the interaction of transmembrane proteins called desmogleins and desmocollins. They are found in tissues subject to mechanical stress such as skin, heart, and uterus.

4. Gap junctions: Gap junctions are channels that allow small molecules and ions to pass between adjacent cells. They are critical for intercellular communication and are found in tissues such as heart, brain and the nervous system.

5. Hemidesmosomes: Hemidesmosomes connect cells to the extracellular matrix through the interaction of transmembrane proteins such as integrins. They are found in tissues such as skin and basement membranes.

Cell junctions are important for maintaining the physical and functional integrity of tissues, regulating cell behavior and communication, and enabling coordinated tissue function. Dysfunction of cell junctions is associated with various diseases such as cancer, skin disorders, and cardiovascular diseases.