Cardiovascular: pulmonary circulation: practice question

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Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Pulmonary arterioles constrict in response to alveolar hypoxia, whereas systemic arterioles dilate in response to hypoxia

Hypoxic pulmonary vasoconstriction diverts blood from poorly ventilated alveoli to well-ventilated ones, improving ventilation-perfusion matching locally. At altitude the whole lung is hypoxic, so vasoconstriction is widespread and pulmonary artery pressure rises. In contrast, hypoxia dilates systemic vessels, increasing flow to tissues.

Option by option

• A. Pulmonary arterioles dilate in response to hypoxia, but the response is overridden by sympathetic tone

  Pulmonary arterioles constrict, not dilate, in hypoxia; sympathetic tone is not the explanation.

• B. Systemic arterioles constrict in hypoxia but the effect is cancelled by high blood flow

  Systemic arterioles dilate in hypoxia, not constrict.

• C. Pulmonary arterioles constrict in response to alveolar hypoxia, whereas systemic arterioles dilate in response to hypoxia (correct)

  Correct. The pulmonary and systemic responses to hypoxia are opposite.

• D. Hypoxia acts on pulmonary veins to raise left atrial pressure

  The effect is on the pulmonary arterioles; left atrial pressure is not raised by hypoxia.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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