Oxygen Carriage

If the oxygen carrying ability of blood relied only upon how much could be dissolved in plasma, our tissues would not survive. The reason being only 3 ml of oxygen dissolves in every litre of blood in a patient breathing room air at sea level. With a normal cardiac output of 5 L/min, this would result in the delivery of 15 ml O2 per minute to the tissues. As the normal resting demand for oxygen is 250 ml/min, this is clearly inadequate. Therefore a system is needed to increase the oxygen carrying capacity of blood so that the delivery of oxygen to the tissues can be improved. This extra help is provided by the presence of red cell Haemoglobin (Hb). Each molecule can carry four molecules of oxygen and there is an average concentration of 150 g/L blood.

Haemoglobin transports 98% of oxygen in the blood.

Quaternary function of oxygen

O2already attached to haemoglobin helps the uptake of further oxygen molecules: