Carbon Dioxide Release

When CO2 in it’s varying guises arrives at the alveolar capillary it is liberated to the alveoli and excreted with the expired air. The mechanism of CO2 release is supported by the pressure gradient of the gas between the capillary 4.5 to 6 kPa and the inspired air <1 kPa. Additionally, because there is a much higher concentration of O2 at the lungs, the oxyHb that forms has a reduced affinity for protons and so the usual rightward direction of the carbonic anhydrase catalysed reaction between CO2 and H2O moves to the left.

The graph illustrates CO2 content variability with PCO2.

Learning Bite

  • CO2 should be considered to be an acid because when dissolved in plasma it reacts with H2O to generate protons
  • With greater quantities of CO2, the reaction is driven rightward with more protons being produced
  • During heavy exercise, the contribution of dissolved CO2 can increase sevenfold and then makes up almost one-third of the total CO2 exchange