Pulmonary circulation holds approximately what percent of circulating blood as a left heart reservoir?

Pulmonary circulation holds approximately what percent of circulating blood as a left heart reservoir?

• A. 5%
• B. 10%
• C. 15%
• D. 20%

Answer: (B)

The pulmonary circulation acts as a low‑pressure, highly compliant reservoir for the left heart. Because it can expand to hold more blood without a large rise in pressure, it stores roughly one‑tenth of the total circulating volume. This allows the left atrium to receive a stable preload and the left ventricle to fill adequately, even when venous return fluctuates. In typical adults, about 9–12% of blood is in the pulmonary circulation, so rounding to 10% is appropriate. The other percentages are outside the usual distribution, making 10% the best choice.

The pulmonary circulation acts as a low‑pressure, highly compliant reservoir for the left heart. Because it can expand to hold more blood without a large rise in pressure, it stores roughly one‑tenth of the total circulating volume. This allows the left atrium to receive a stable preload and the left ventricle to fill adequately, even when venous return fluctuates. In typical adults, about 9–12% of blood is in the pulmonary circulation, so rounding to 10% is appropriate. The other percentages are outside the usual distribution, making 10% the best choice.