Blood flow is ________ proportional to the difference in blood pressure. Blood flow is ________ proportional to the total peripheral resistance.

• A. Directly; Inversely
• B. Directly; Directly
• C. Inversely; Directly
• D. Inversely; Inversely

Answer: (A)

Blood flow is driven by the pressure difference across the circulation and opposed by resistance. When the pressure gradient increases, the driving force pushing blood through the vessels rises, so flow increases in direct proportion to that gradient, provided resistance stays the same. Conversely, total peripheral resistance acts like a brake: as resistance rises, flow falls, and as resistance falls, flow rises. This relationship is captured by flow = ΔP / R, so flow is directly proportional to the pressure difference and inversely proportional to the resistance. In the systemic circuit, arteriolar radius largely sets total peripheral resistance, and even small changes in radius can markedly alter flow due to how resistance scales with radius. Therefore, the correct pairing is: blood flow is directly proportional to the difference in blood pressure and inversely proportional to the total peripheral resistance.