|The Oxygen Dissociation Curve|
|The oxygen dissociation curve is a graph that
shows the percent saturation of hemoglobin at various partial pressures of
oxygen. Commonly a curve may be expressed with the P50
value. This is a value which tells the pressure at which the
erythrocytes are fifty percent saturated with oxygen. (Bouverot,
1985). The purpose of an oxygen dissociation curve
is to show the equilibrium of
oxyhemoglobin and nonbonded hemoglobin at various partial pressures
(Oxygen Dissociation Curve).
At high partial pressures of oxygen, usually in the lungs, hemoglobin
binds to oxygen to form oxyhemoglobin. When the blood is fully
saturated all the erythrocytes are in the form of oxyhemoglobin. As
the erythrocytes travel to tissues deprived of oxygen the partial pressure
of oxygen will decrease. Consequently, the oxyhemoglobin releases
the oxygen to form hemoglobin (Schmidt-Nielsen, 1997).
The sigmoid shape of the oxygen dissociation curve is a result of the cooperative binding of oxygen to the four polypeptide chains. Cooperative binding is the characteristic of a hemoglobin to have a greater ability to bind oxygen after a subunit has bound oxygen (Oxygen Dissociation Curve). Thus, hemoglobin is most attracted to oxygen when three of the four polypeptide chains are bound to oxygen.
Hypothetical oxygen dissociation graph. Changes in temperature, pH, and organic phosphates like DPG directly effect the dissociation of oxygen. Image used with permission of The American Society of Health-System Pharmacists, Inc
Factors that Influence Oxygen Binding
This web site was created as a class assignment for Animal Physiology. Please direct correspondence to firstname.lastname@example.org.
Last Updated November 28, 1999