A 20-year-old physiology student awakens to get ready for classes. When he arise

Question

A 20-year-old physiology student awakens to get ready for classes. When he arises from a lying down to a standing up position, changes occur to his lungs. Which of the following describes the alteration that occur in the alveoli at the top of his lungs compared with those at the bottom of the lungs?

a. Exhibit greater compliance

b. Have a lower ventilation-perfusion (ventilation-blood flow) ratio

c. Have larger radii

d. Receive a greater percentage of the pulmonary blood flow

e. Receive a greater percentage of the tidal volume

Defend your answer by describing why each of the other answers are not correct

Explanation / Answer

Answer is c

Under the influence of gravity the weight of the lung strethes structures at the top of the lungs and compress those at the bottom. Thus alveoli are larger at the top of the lung. Because they are streched those alevoli are less complaint and smaller changes in volume with changes in intrapleural pressure upon inspiration . Thus they are less well ventilated. Because pulmonary artery pressure are relatively low blood flow to these alevoli also is low, however ventilation is not as A low as blood flow thus ventilation is high

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