A region of the cell surface, of variable size, and situated just below the apical border where the membranes of adjacent cells are fused to form a pentalaminar structure. In simple epithelial layers tight junctions often form a continuous layer (the zonula occludens). Their function appears to be the provision of areas of contact between cells of enhanced permeability and low electrical resistance. They occur in tissues such as the blood–brain barrier and cardiac muscle, where such features are advantageous.
Subjects: Zoology and Animal Sciences.