What is the function of capillary pericytes?

• A. Phagocytose circulating bacteria
• B. Stabilize capillary walls, regulate diameter and blood flow, contribute to angiogenesis and blood-brain barrier integrity
• C. Pump blood through capillaries
• D. Form the endothelial lining

Answer: (B)

Pericytes are mural cells that wrap around the tiny vessels in capillary walls. Their main role is to stabilize the capillary structure and actively regulate what happens at the vessel wall. They can contract and relax to adjust capillary diameter, shaping local blood flow, and they communicate with endothelial cells to promote vessel stability and proper barrier function. In the brain, pericytes are crucial for maintaining the blood-brain barrier by supporting tight junctions and the basement membrane, helping keep the neural environment protected and properly regulated. They also secrete signals that promote angiogenesis and vessel maturation, so they’re involved in new vessel growth and remodeling.

This is why the option describing stabilization of capillary walls, control of diameter and blood flow, and contributions to angiogenesis and blood-brain barrier integrity best fits the role of capillary pericytes. They do not primarily phagocytose bacteria—that task belongs to immune cells like macrophages and microglia—nor do they pump blood through capillaries (that’s the job of the heart and arterial system), nor form the endothelial lining (that’s the role of endothelial cells).