During heavy exercise the cardiac output (CO) increases upto five fold while pulmonary arterial pressure rises very little. This physiological ability of the pulmonary circulation is best explained by
**Core Concept**
The pulmonary circulation's ability to accommodate increased cardiac output without a significant rise in pulmonary arterial pressure is attributed to its unique anatomical and physiological characteristics. This phenomenon is crucial during heavy exercise when cardiac output surges to meet the increased oxygen demands of the body.
**Why the Correct Answer is Right**
The correct answer lies in the high capacitance of the pulmonary vasculature. The pulmonary circulation has a large volume of blood in the capillaries, which allows for a significant increase in cardiac output without a substantial rise in pulmonary arterial pressure. This is due to the low resistance and high compliance of the pulmonary vasculature, which enables it to accommodate the increased blood flow without a significant increase in pressure. The pulmonary vasculature's high capacitance is also facilitated by the extensive network of pulmonary capillaries, which provides a large surface area for gas exchange.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not address the specific physiological ability of the pulmonary circulation to accommodate increased cardiac output without a significant rise in pulmonary arterial pressure.
**Option B:** This option is incorrect as it refers to the systemic circulation, which has a much lower capacitance than the pulmonary circulation and is not relevant to the question.
**Option C:** This option is incorrect as it refers to the pulmonary vascular resistance, which is low in the pulmonary circulation but does not explain the high capacitance of the pulmonary vasculature.
**Clinical Pearl / High-Yield Fact**
The high capacitance of the pulmonary vasculature is a critical adaptation that enables the body to accommodate increased cardiac output during heavy exercise without causing pulmonary congestion or hypertension.
**Correct Answer:** C.