Question

Hypoxic pulmonary vasoconstriction is best described as which of the following?

• A. Irreversible pulmonary vasoconstriction due to hypoxia
• B. Reversible pulmonary vasoconstriction due to hypoxia
• C. Directs blood to poorly ventilated areas
• D. Occurs hours after pulmonary vasoconstriction

Hint:

It is an active, reversible response diverting blood away from poorly ventilated lung.

Answer 1

The Correct Option is B

Step 1: Define HPV. When an alveolus is poorly ventilated and its local oxygen falls, the nearby small pulmonary resistance arteries actively tighten - this is hypoxic pulmonary vasoconstriction.

Step 2: Understand its goal. By squeezing vessels in low-oxygen zones, the lung shunts blood toward well aerated segments, sharpening ventilation-perfusion matching and protecting arterial oxygen levels.

Step 3: Note the dynamics. The response is prompt (seconds to minutes) and fully reversible - restoring alveolar oxygen relaxes the arteries and reopens flow.

Step 4: Test the options. It is not irreversible (a fails), it diverts blood AWAY from poorly ventilated areas rather than toward them (c fails), and it is not delayed by hours (d fails). The accurate statement is reversible pulmonary vasoconstriction due to hypoxia.

\[\boxed{\text{Reversible pulmonary vasoconstriction due to hypoxia}}\]