Which feature reduces paracellular diffusion across the BBB?

Which feature reduces paracellular diffusion across the BBB?

• A. Astrocytic end-feet
• B. Low pinocytotic activity reduces transcellular transport
• C. Tight endothelial junctions
• D. Pericyte coverage of capillaries

Answer: (C)

Paracellular diffusion happens when substances move between adjacent endothelial cells. In the brain, this pathway is minimized by tight junctions between the endothelial cells, which form a dense seal and create a high barrier to intercellular passage. These tight junctions—made of proteins like claudins and occludins—restrict the paracellular route, keeping the brain protected from many solutes. Astrocyte end-feet and pericytes support and regulate the barrier, but the direct feature that stops paracellular leakage is the tight endothelial junctions. Low pinocytotic activity reduces transport through the cell (transcellular), not between cells, so it doesn’t address paracellular diffusion.

Paracellular diffusion happens when substances move between adjacent endothelial cells. In the brain, this pathway is minimized by tight junctions between the endothelial cells, which form a dense seal and create a high barrier to intercellular passage. These tight junctions—made of proteins like claudins and occludins—restrict the paracellular route, keeping the brain protected from many solutes. Astrocyte end-feet and pericytes support and regulate the barrier, but the direct feature that stops paracellular leakage is the tight endothelial junctions. Low pinocytotic activity reduces transport through the cell (transcellular), not between cells, so it doesn’t address paracellular diffusion.