explain tight junction ??
Answers
Answer:
Epithelia are sheets of cells that provide the interface between masses of cells and a cavity or space (a lumen).
The portion of the cell exposed to the lumen is called its apical surface.
The rest of the cell (i.e., its sides and base) make up the basolateral surface.
Tight junctions seal adjacent epithelial cells in a narrow band just beneath their apical surface. They consist of a network of claudins and other proteins.
Tight junctions perform two vital functions:
They limit the passage of molecules and ions through the space between cells. So most materials must actually enter the cells (by diffusion or active transport) in order to pass through the tissue. This pathway provides tighter control over what substances are allowed through.
They block the movement of integral membrane proteins (red and green ovals) between the apical and basolateral surfaces of the cell. Thus the special functions of each surface, for example
receptor-mediated endocytosis at the apical surface
exocytosis at the basolateral surface
can be preserved.
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Tight junctions are areas where the membranes of two adjacent cells join together to form a barrier. The cellmembranes are connected by strands of transmembrane proteins such as claudins and occludins