Tight junctions are the most apical intercellular junctions of epithelial and endothelial cells
and create a regulatable semipermeable diffusion barrier between individual cells. On a
cellular level, they form an intramembrane diffusion fence that restricts the intermixing of
apical and basolateral membrane components. In addition to these well defined functions,
more recent evidence suggests that tight junctions are also involved in basic cellular
processes like the regulation of cell growth and differentiation.