Question

The percentage of body's blood volume that veins hold is:

• A. \( 40% \)
• B. \( 60% \)
• C. \( 50% \)
• D. \( 30% \)

Hint:

Think of your cardiovascular system as having two distinct halves: - Arteries = Pressure Reservoirs: They carry small volumes of blood under high pressure to drive perfusion. - Veins = Volume Reservoirs (Capacitance Vessels): They hold roughly $60%$ of your total blood supply under low pressure, acting as a buffer that the body can tap into during exercise or blood loss.

Answer 1

The Correct Option is B

Concept: The human circulatory system is divided into functional circuits with varying pressure and volume characteristics. Structurally, veins and venules have thinner walls, less smooth muscle, and much higher compliance (stretchability) than their thick-walled arterial counterparts. This structural flexibility allows the venous system to expand and hold large volumes of blood at very low internal pressures.

Step 1: Reviewing systemic blood volume distribution.
In a resting adult human body, the total blood volume is distributed across the cardiovascular loops approximately as follows:
• Systemic Arteries and Arterioles: $\approx 13% - 15%$
• Systemic Capillaries: $\approx 5%$
• Pulmonary Circuit (lungs): $\approx 9% - 12%$
• Heart Chambers: $\approx 7% - 10%$
• Systemic Veins and Venules: $\approx 60% - 64%$

Step 2: Concluding the physiological designation.
Because veins hold nearly two-thirds of the body's total blood volume under resting conditions, physiology textbooks refer to the venous system as the capacitance vessels or the primary reservoir of the circulatory system. If the body experiences trauma or blood loss, sympathetic nerve stimulation constricts these veins, shifting this stored blood back into active arterial circulation to maintain central blood pressure. This matches Option (B).