Physiology of gas exchange

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.
Last modified: Saturday, 4 June 2011, 8:49 AM