If the precapillary sphincter dilates, the claim that this causes less blood into capillaries, less volume, and decreased Blood Capillary Pressure (BCP) is true or false?

• A. True
• B. False
• C. Not enough information
• D. It increases Blood Capillary Pressure

Answer: (B)

Precapillary sphincters control how much arterial blood enters the capillary bed. When they dilate, resistance at the entrance drops, so more blood can flow into the capillaries. This increases the capillary blood volume and tends to raise capillary hydrostatic pressure. Therefore the claim that dilation causes less blood into capillaries and decreased Blood Capillary Pressure is not correct; the opposite effect—more blood entering and higher capillary pressure—is expected.