Transport of Gases by blood

CO2 Transport:
  • CO2 diffuses into blood (in solution); some carried in solution as CO2 (about 7%);
  • CO2 diffuses along conc gradient into red cells;
  • where carbonic anhydrase is present which converts CO2 to carbonic acid
  • which dissasociates into hydrogencarbonate ions and H+
  • hydrogencarbonate diffuses out into blood plasma;
  • this major form of CO2 carried (about 86%);
  • buffering by haemoglobin (of H+)
  • in lungs reactions reversed (due to changes in conc gradients);
  • CO2 diffuses out into alveoli (along conc gradient);

O2 Transport


  • High partial pressure of oxygen in the lungs
  • haemoglobin in lung capillaries has high affinity for oxygen;
  • therefore becomes saturated with oxygen (Haemoglobin combining with oxygen to give oxyhaemoglobin)


  • ODC curve shifted to right in muscle (Bohr effect)
  • because of high carbon dioxide concentration/low pH and higher temperature;
  • haemoglobin in muscle therefore has low affinity for oxygen;
  • therefore oxyhaemoglobin dissociates/’gives up’ oxygen readily;
  • therefore more oxygen available for muscle cells;
  • Diffusion of oxygen into blood/tissues;