The blood-brain barrier (BBB) is formed primarily by which structural element?

• A Thick basement membranes of cerebral capillaries preventing macromolecular passage
• B Tight junctions (zonulae occludentes) between cerebral capillary endothelial cells, with absent fenestrations and minimal pinocytosis ✓
• C Astrocytic end-feet that physically block the capillary lumen
• D Pericytes lining the outer surface of capillaries, phagocytosing unwanted molecules

Explanation

The BBB is primarily formed by specialized cerebral capillary endothelial cells linked by claudin-5, occludin, and ZO-1 tight junctions that seal the intercellular cleft, preventing paracellular transport. These endothelial cells also lack fenestrations and have minimal transcytotic vesicles, further restricting movement of large molecules, ions, and many drugs. Astrocytic end-feet and pericytes are important inducers and regulators of BBB properties but do not themselves form the physical barrier. Lipid-soluble molecules (O2, CO2, ethanol, many anaesthetics) cross freely; most polar drugs and proteins are excluded.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.