What Are Tight Junctions?

Tight junctions, also known as occluded zonules, are a barrier that is virtually impenetrable to liquids that are formed by adjacent cell membranes. It is a tightly connected area between two cells. It is a type of cell junction complex found only in vertebrates. In invertebrates, the corresponding connection is a bulkhead connection.

tight connection

From a structural point of view, the tight connection between two adjacent cells is a row of cables that are repeatedly formed by tight protein particles that connect two adjacent cells. The diameter of these protein particles is only a few nanometers, and they form continuous fibers. It is like a welding wire, connecting adjacent cells and closing the gap between cells.

Tight connection is an impermeable connection, and it is commonly found in vertebrates.

Tightly connected collections perform three important functions:

Fix the cells together

Prevents the top and bottom side integration membrane proteins from diffusing from the side, thereby helping to maintain the polarity of the cells, allowing specific functions of each surface to be maintained. Its purpose is to transport across the membrane.

Prevent molecules and ions from passing through the interstitial space. Therefore the substance must enter the cell essentially (by diffusion or active transport) to pass through the tissue. This approach provides the ability to control what substances are allowed to pass. (Closely connected

Classified by the ability of tight junctions to prevent water and solution from moving, the epithelium is divided into 'tight' and 'leaking':

Tight epithelium has a tight junction that prevents movement between most cells. For example, the distally curved tubules and ureters in the kidney.

Leaky epithelium does not have tight junctions, or only less complex tight junctions. For example, the proximal tubule of the kidney is a very leaky epithelium, with only two to three connected occluders and showing infrequent large fissure interruptions.