Effect of pH and Temperature
on Oxygen Transport
In addition to changes in PO2, the loading and unloading reac- tions are influenced by changes in the affinity (bond strength) of hemoglobin for oxygen. Such changes ensure that active skeletal muscles will receive more oxygen from the blood than they do at rest. This occurs as a result of the lowered pH and increased temperature in exercising muscles.
The affinity is decreased when the pH is lowered and increased when the pH is raised; this is called the Bohr effect. When the affinity of hemoglobin for oxygen is reduced, there is slightly less loading of the blood with oxygen in the lungs but greater unloading of oxygen in the tissues. The net effect is that the tissues receive more oxygen when the blood pH is lowered (table 16.8). Since the pH can be decreased by carbon dioxide (through the formation of carbonic acid), the Bohr effect helps to provide more oxygen to the tissues when their carbon diox- ide output is increased by a faster metabolism.
When you look at oxyhemoglobin dissociation curves graphed at different pH values, you can see that the disso- ciation curve is shifted to the right by a lowering of pH and shifted to the left by a rise in pH
on Oxygen Transport
In addition to changes in PO2, the loading and unloading reac- tions are influenced by changes in the affinity (bond strength) of hemoglobin for oxygen. Such changes ensure that active skeletal muscles will receive more oxygen from the blood than they do at rest. This occurs as a result of the lowered pH and increased temperature in exercising muscles.
The affinity is decreased when the pH is lowered and increased when the pH is raised; this is called the Bohr effect. When the affinity of hemoglobin for oxygen is reduced, there is slightly less loading of the blood with oxygen in the lungs but greater unloading of oxygen in the tissues. The net effect is that the tissues receive more oxygen when the blood pH is lowered (table 16.8). Since the pH can be decreased by carbon dioxide (through the formation of carbonic acid), the Bohr effect helps to provide more oxygen to the tissues when their carbon diox- ide output is increased by a faster metabolism.
When you look at oxyhemoglobin dissociation curves graphed at different pH values, you can see that the disso- ciation curve is shifted to the right by a lowering of pH and shifted to the left by a rise in pH
saturation for arterial and venous blood), you will see that a
shift to the right of the curve indicates a greater unloading of
oxygen. A shift to the left, conversely, indicates less unloading
but slightly more oxygen loading in the lungs.
When oxyhemoglobin dissociation curves are constructed at different temperatures, the curve moves rightward as the temperature increases. The rightward shift of the curve indi- cates that the affinity of hemoglobin for oxygen is decreased by a rise in temperature. An increase in temperature weakens the bond between hemoglobin and oxygen and thus has the same effect as a fall in pH. At higher temperatures, therefore, more oxygen is unloaded to the tissues than would be the case if the bond strength were constant. This effect can significantly enhance the delivery of oxygen to muscles that are warmed during exercise
When oxyhemoglobin dissociation curves are constructed at different temperatures, the curve moves rightward as the temperature increases. The rightward shift of the curve indi- cates that the affinity of hemoglobin for oxygen is decreased by a rise in temperature. An increase in temperature weakens the bond between hemoglobin and oxygen and thus has the same effect as a fall in pH. At higher temperatures, therefore, more oxygen is unloaded to the tissues than would be the case if the bond strength were constant. This effect can significantly enhance the delivery of oxygen to muscles that are warmed during exercise
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