During standing. In apex of lung -
Ans. is "c" i.e., V/Q is high o Due to gravity, the apical alveoli are both underventilated and underperfused while the basal alveoli are both overventilated and overperfused.o However, gravity affects perfusion much more than it affects ventilation.o Hence, apical alveoli are more underperfused than underventilated while the basal alveoli are more overperfused than overventilated.o Therefore, V/Q is maximun at apex (about 3.0) and least at base (about 0.6).o Since ventilation is far in excess of perfusion at apex, comparatively little oxygen is transferred from the alveoli to the blood, and CO2 transferred to the alveoli is also less.o Hence the gas tension at the apices are quiet close to those of inspired air, i.e., High PaO2 and low PaCO2.o On the other hand, at the base of lung perfusion is better than ventilation; Hence PaO2 and PaCO2 of basal alveoli are quiet close to those of pulmonary artery, i. e., low PaO, and high PaCO2o In simple words, ventilation-perfusion mismatch is responsible for high PO2 with low PCO2 at apex and Low PO2 with high PCO2 at base.
Blood flow is high
Ventilation is high
V/Q is high
V/Q is low
Functional Anatomy - Respiratory System