Compared with the apex of the lung, the base of the lung has

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[VII C; Figure 4.10; Table 4.5]. Ventilation and perfusion of the lung are not distributed uniformly. Both are lowest at the apex and highest at the base. However, the differences for ventilation are not as great as for perfusion, making the ventilation/ perfusion (V/Q) ratios higher at the apex and lower at the base. As a result, gas exchange is more efficient at the apex and less efficient at the base. Therefore, blood leaving the apex will have a higher $\mathrm{PO}_{2}$ and a lower $\mathrm{PCO}_{2}$.

Compared with the Apex of the Lung, the Base of the Lung