T RANSPORT OF G ASES

T RANSPORT OF G ASES Blood is the medium of transport for O and CO . About per cent of O is transported by RBCs in the blood. The remaining per cent of O is carried in a dissolved state through the plasma. Nearly - per cent of CO is transported by RBCs whereas per cent of it is carried as bicarbonate. About per cent of CO is carried in a dissolved state through plasma. . . Transport of Oxygen Haemoglobin is a red coloured iron containing pigment present in the RBCs. O can bind with haemoglobin in a reversible manner to form oxyhaemoglobin . Each haemoglobin molecule can carry a maximum of four molecules of O . Binding of oxygen with haemoglobin is primarily related to partial pressure of O . Partial pressure of CO , hydrogen ion concentration and temperature are the other factors which can interfere with this binding. A sigmoid curve is obtained when percentage saturation of haemoglobin with O is plotted against the pO . This curve is called the Oxygen dissociation curve (Figure . ) and is highly useful in studying the effect of factors like pCO , H + concentration, etc., on binding of O with haemoglobin. In the alveoli, where there is high pO , low pCO , lesser H + concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin, whereas in the tissues, where low pO , high pCO , high H + concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin. This clearly indicates that O gets bound to haemoglobin in the lung surface and gets dissociated at the tissues. Every ml of oxygenated blood can deliver around ml of O to the tissues under normal physiological conditions. . . Transport of Carbon dioxide CO is carried by haemoglobin as carbamino-haemoglobin (about - per cent). This binding is related to the partial pressure of