How is oxygen transported in blood; what is mean by O2 dissociation curve?


How is oxygen transported in blood; what is mean by O2 dissociation curve?

1) Transport of Oxygen:

In mammalian blood, the O2 carrier respiratory pigment is haemoglobin. The maximum amount of O2 which the normal human blood can absorb is 20 ml / 100ml of blood. When 02 passes from the lung alveoli into the lung capillaries, it diffuses into the blood and unites with haemoglobin to form oxyhaemoglobin.


Hb + O2 -> HbO2

(Haemoblogin Oxyhaemoblogin)

This reaction is a reversible one. The oxyhaemoglobin reaches the place of diffusion. The liberation of O2 from the blood to the tissues is just as important as its rapid absorption by the blood during its passage through the lungs.

HbO2 -> Hb + O2


(Oxyhaemoglobin Reduced haemoglobin)

The reduced haemoglobin is again transported via blood to the lungs and the cycle is repeated.

Oxygen Dissociation curve:

Normally the haemoglobin combines with O2 to form oxyhaemoglobin. Each iron atom can attach one molecule of O2 and when all sites are occupied, the haemoglobin cannot take on any­more since it is fully loaded or saturated. This saturation varies greatly. In other words, the proportion of oxyhaemoglobin to haemoglobin present in the blood at any time is dependent on the tension of 02 in the blood.


This is known as dissociation curve of oxyhaemoglobin. In this way the actual relationship between the partial pressure of O2 and the degree of satura­tion of haemoglobin dissociation can be measured. The following factors affect the oxygen dissociation curve.

1. Partial pressure of O2

2. Partial pressure of CO2

3. Effect of temperature


4. Effect of haemoglobin

5. Effect of pH

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