Which of the following occurs during normal inspiration?

a. Alveoli at the apexes expand less than those at the bases.
b. Alveoli at the apexes expand more than those at the bases.
c. Alveoli at the bases expand less than those at the apexes.
d. Central alveoli expand more than those at the periphery.

ANS: A
Despite their higher volume, alveoli at the apexes expand less during inspiration than alveoli at the bases or periphery. This is due to their respective positions on the pressure volume curves (Figure 11-14). The apical alveoli are on the flatter or less compliant portion of the curve and thus for any change in pressure there is only a small change in volume. The alveoli in the lung base are on the steep part of the curve, so even small changes in pressure result in comparatively large changes in volume.