Question

In ventilation-perfusion matching, there are local responses of smooth muscles lining the pulmonary vasculature that occur when those muscles detect locally low P. This can occur, for example, if the nearby alveoli are not properly ventilated with fresh atmospheric air because they are damaged or blocked. The outcome of ventilation-perfusion matching is to decrease blood flow through these damaged areas and increase blood flow through well-ventilated regions of the lungs. How might this happen?

A The smooth muscles in the vasculature near the poorly-ventilated alveoli could relax.

B The smooth muscles in the vasculature near the poorly-ventilated alveoli could constrict.

C The smooth muscles in the vasculature near the poorly-ventilated alveoli could pull the damaged alveoli closer to the walls of the nearby capillaries.

D The smooth muscles in the vasculature near the poorly-ventilated alveoli could push the damaged alveoli farther away from the walls of the nearby capillaries.

Answer 1

B. The smooth muscle in the vasculature near poorly ventilated alveoli could constrict.

• Blood flow through vessel is directly proportional to 4th power of radius.

• When the smooth muscle constrict, the diameter of Blood vessel also decrease (vasoconstriction). This decreases blood flow to poorly ventilated alveoli.

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