VPB 121: Veterinary Physiology - II (2+1)

PHYSIOLOGY OF GAS EXCHANGE

• Ventilation brings O₂ to the alveoli and removes CO₂. Because O₂ is being consumed in the tissues, a pressure difference exists for its diffusion from alveoli to venous blood (which then becomes arterial) and from arte­rial blood to the tissues. Because CO₂ is being produced in the tissues, a pressure difference exists for its diffusion from tissue to arterial blood (which then becomes venous) and from venous blood to the alveoli. (Animation831-After title correction)

Gases	Venous Blood	Alveolar Air	Arterial Blood	Tissues
O2	40	104	100	30 or less
CO2	45	40	40	50 or more
N2	569	569	569	569
Water vapor	47	47	47	47
Total	701	760	756	696

Values are in mm of Hg

• The total pressure in venous blood is somewhat less than atmospheric pressure because the volume of CO₂ pro­duced is lower than the volume of O₂ con­sumed.
• As because not all of the blood going to the lungs is arterialized (nonperfused alveoli) the difference in PO₂ exists.