Tight Junction

**Semantic type:** Cell Component

**Definition:** Found near the apical surface of cells in simple epithelia. Forms a sealing "gasket" around the cell by the fusion of adjacent cell membranes which encircle the apical cell surface like a belt or fence. Prevents fluid moving through the intercellular gap and the lateral diffusion of intrinsic membrane proteins between apical and basolateral domains of the plasma membrane as well as occludes the movement of solute molecules between cells. Various proteins components of this junction have been identified, but how they are linked to form the ultrastructure of the junction is not known.

**Synonyms:** - Occluding Junction - Zonula Occludens