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Sunday, February 3, 2019

Oxygen transport: hemoglobin affinity for oxygen


Oxygen transport? 

The solubility of oxygen in water is little that is why only 1.5% of oxygen is dissolved in blood plasma. The remaining portion of oxygen (98.5%) is transported by hemoglobin as Oxyhaemoglobin (Hb-O2) within Red Blood Cells.
The hemoglobin contains four atoms of iron in its heme portion each of which is capable of binding to the O2 molecule in a reversible form of reaction to form Oxyhaemoglobin.
The binding of O2 with hemoglobin depends on an important factor that is partial pressure of oxygen.
When the partial pressure is high, hemoglobin binds with large amounts of O2 and is almost 100% saturated When the partial pressure of oxygen is low, hemoglobin is only partially saturated (i.e. less amount of Hb is converted to Hb-O2).
In pulmonary capillaries where the partial pressure of oxygen is high a lot of oxygen binds to hemoglobin whereas in tissue capillaries where the partial pressure of oxygen is lower, hemoglobin doesn’t hold a greater amount of oxygen and the dissolved oxygen is unloaded through diffusion into tissue cells.

Factors affecting the affinity of Hemoglobin for oxygen? 

  1. Acidity: As acidity increases (PH decreases) the affinity of hemoglobin for oxygen decreases and oxygen dissociates readily from hemoglobin.
  2. The partial pressure of carbon dioxide: The effect of the partial pressure of carbon dioxide is similar to that of an increase in acidity. As the partial pressure of carbon dioxide raises the affinity of hemoglobin for oxygen decreases.
  3. Temperature: An increase in temperature results in a decrease in the affinity of hemoglobin for oxygen. In contrast during hypothermia (lower body temperature), the larger amount of oxygen binds to hemoglobin.
  4. BPG: It is called 2,3 bisphosphoglycerate, a substance formed in Red Blood Cells during the breakdown of glucose to produce ATP in a process called glycolysis. It decreases the affinity of hemoglobin for oxygen.

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