• 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;