Tight junctions, desmosomes, & gap junctions

TIGHT JUNCTION:

A series of integral protein molecules in the plasma membranes of adjacent cells fuse together, forming an impermeable junction that encircles the cell. Tight junctions help prevent molecules from passing throughout the extracellular space between adjacent cells.

DESMOSOMES:

Anchoring junctions-mechanical couplings scattered like rivets along the sides of abutting cells that prevent their separation. They not only bind neighboring cells together, they also contribute to a continuous strong internal network. This arrangement distributes tension throughout a cellular sheet and reduces the chance of tearing when it is subjected to strong pulling forces. Desmosomes are abundant in tissues subjected to large mechanical stress, like skin and heart muscle.

GAP JUNCTIONS:

A communicating junction. That allows chemical substances to pass between adjacent cells. At gap junctions that adjacent plasma membranes are very close, and the cells are connected by hollow cylinder called connexons. Gap junctions are in electrically excited tissues, such as heart and smooth muscle, where ion passage from cell to cell helps synchronize their electrical activity and contraction.