Why does the affinity of haemoglobin's for oxygen decrease at high altitudes?

Question

My class 12 NCERT book says, Pg 226> The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding affinity of haemoglobin and by increasing breathing rate.Why should the haemoglobin binding capacity decrease at high altitude?I think it should increase for better oxygen transfer and uptake from air. The concentrtion of oxygen in the atmosphere decreases with height. Hence, if the haemoglobin binding increases, we will be able to draw more oxygen from the air and transport it to the cells.

Answer 1

Hello!

This fact is a little counter-intuitive at first. There are two things going on simultaneously. The first is there are more red blood cells to accept the small amount of oxygen around. This means that there is a higher chance for a RBC to pick up its first oxygen, which then will allow its affinity to greatly increase due to cooperativity.

However, once your RBCs enter regions where oxygen is needed, having a higher binding affinity is actually the opposite of what you want. If the affinity for oxygen were higher than normal, it would not release the oxygen in the regions that require it.

By combining the two (higher RBC count and decreased affinity) it allows for the minimal oxygen to be scavenged from the air, and for it to be fully released instead of being pulled from the air and then sequestered in the RBCs, which would be useless for the cell.

If you have more questions, please feel free to contact me and we can set up time to discuss this more!

Dr. CJ