USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

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Which type of shunt bypasses the pulmonary circulation and may lead to pulmonary hypertension?

Physiological Shunt
Anatomic Shunt
Left-to-Right Shunt
Obstructive Lung Capacity

The correct answer is: Left-to-Right Shunt

A left-to-right shunt is a type of shunt that allows blood to bypass the pulmonary circulation and mix with oxygenated blood, leading to an increased blood flow to the lungs. This increased blood flow can lead to damage and narrowing of blood vessels in the lungs, resulting in pulmonary hypertension. Option A, physiological shunt, refers to a normal amount of blood that does not get oxygenated in the lungs and mixes with oxygenated blood. This does not result in an increased blood flow and thus does not lead to pulmonary hypertension. Option B, anatomic shunt, refers to a structural abnormality that creates a pathway for blood to bypass the lungs and mix with oxygenated blood. This also does not necessarily result in an increased blood flow and is different from a left-to-right shunt. Option D, obstructive lung capacity, refers to a condition where the lungs have difficulty exhaling air. While this condition may contribute to pulmonary hypertension, it is not a type of shunt and is not directly related to bypassing the pulmonary circulation.