Transport of Gases

Blood is the transport medium for both respiratory gases, but it carries them in very different ways because of their very different solubilities in water-based plasma. Oxygen is poorly soluble in plasma, so almost all of it must be carried bound to haemoglobin inside red blood cells, with only a small fraction travelling dissolved in plasma. Carbon dioxide, being far more soluble, is carried by three separate routes at once - dissolved in plasma, bound to haemoglobin, and (the majority) converted to bicarbonate ions in plasma. Which route a given CO2 molecule takes, and how readily haemoglobin releases its bound O2, both depend on local conditions such as partial pressure, temperature, pH and hydrogen-ion concentration - conditions that differ shar …