Question

Why does Hb combine with O2 in the capillaries at the lungs and separate at the tissue capillaries

Answer 1

Ans- Hb is the structure present in the red blood cells which carries oxygen from lungs to the tissues. In the lungs capillaries, the partial pressure of oxygen is high, H+ concentration is low, partial pressure of CO2 is low and temperature is also low, it leads to binding of Hb with oxygen. When Hb has no bound oxygen or carbon dioxide it has unbound confirmation. Therefore on availability of oxygen at the lungs, it binds to first molecule of oxygen. Thus induces change in shape of Hb molecule which increases its ability to bind to other three oxygen molecules. Thus it carries oxygen binded to it to the tissues capillaries.

At the tissues area , where partial pressure of oxygen is low, while partial pressure of carbon dioxide, H+ ion concentration and temperature are high, it leads to dissociation of Hb from oxygen. Here due to higher concentration of carbon dioxide, the pH of blood changes leading to another change in shape of Hb which increases its ability to bind with carbon dioxide and decreases it's ability to bind with oxygen.With the loss of the first oxygen molecule, and the binding of the first carbon dioxide molecule, yet another change in shape occurs, which further decreases the ability to bind oxygen, and increases the ability to bind carbon dioxide. The oxygen bound to the hemoglobin is released into the blood's plasma and absorbed into the tissues, and the carbon dioxide in the tissues is bound to the hemoglobin.