Physiology of Finfish and Shellfish

2.1.23. Oxygen dissociation curve

At high oxygen concentration the hemoglobin (Hb) combines with oxygen to form oxyhemoglobin(HbO₂)

4Hb + 4 O_{2 →} 4HbO₂

At low concentration, oxygen is given up again and the reaction proceeds to the left i.e

Hb + O_{2 →} HbO₂

The hemoglobin is saturated according to the given O₂ concentration. At any given oxygen concentration, there is a definite proportion between the amount of hemoglobin and oxyhemoglobin. Thus, by plotting the oxyhemoglobin for a given oxygen concentration, a curve oxygen hemoglobin dissociation curve is obtained. This curve will be of normally in sigmoid shape.

In some animals, the blood has high affinity to oxygen (it gives up oxygen less readily), and the dissociation curve is located further to the left. The blood of others gives up oxygen more readily (the affinity and oxygen is lower), and the dissociation curve is located further to the right. Binding of oxygen to hemoglobin is affected by several factors.