Which vessels have the lowest blood pressure?

• A. Arteries
• B. Capillaries
• C. Veins
• D. Aorta

Answer: (C)

Blood pressure is generated by the heart and diminishes as blood moves away from it. Arteries, especially the aorta, experience the highest pressures right after the heart contracts. As blood travels through the capillary beds, resistance and the enormous total cross-sectional area cause a large drop in pressure, making capillaries relatively low but still higher than veins. By the time blood returns to the heart via the venous system, pressures are at their lowest. Veins have thin walls and large lumens, with valves and surrounding muscles helping push blood back toward the heart against gravity. Typical venous pressures are only a few millimeters of mercury, far lower than arterial and capillary pressures. This combination of distance from the heart, vessel structure, and supportive mechanisms results in veins having the lowest blood pressure.