O2 CO2 Gas Exchange Diffusion Ventilation allows the alveolar air to represent an “infinite” oxygen supply at a PO2 of 100 mmHg O2 Blood flow allows the alveolar capillaries to represent an “infinite” oxygen sink at PO2 of 40 mmHg Ventilation allows the alveolar air to represent an “infinite” carbon dioxide sink at a PCO2 of 40 mmHg CO2 Blood flow allows the alveolar capillaries to represent an “infinite” carbon dioxide supply at PCO2 of 45 mmHg Fick’s first law Flux = C (P1 - P2) Where: (P1 - P2) = pressure gradient C = conductance