4.1 O2 and CO2 transport in the blood
You've seen how gradients between PO2 and PCO2 drive gas exchange in the alveoli. But how are these gases carried in the blood? Small amounts of O2 (~0.3%) and CO2 (~3%) dissolve directly into the plasma. However, such concentrations are not sufficient to fulfil the metabolic demands of the body. The main transport of O2 and CO2 in the blood is mediated via haemoglobin molecules and bicarbonate ions, respectively.