Question

Which two of the following changes (I-IV) usually tend to occur in the plain dwellers, when they move to high altitudes (3500 m or more)?
I. Increase in red blood cell size.
II. Increase in red blood cell production.
III. Increased breathing rate.
IV. Increase in thrombocyte count.
Changes occurring are

• A. II and III
• B. III and IV
• C. I and IV
• D. I and II

Answer 1

The correct option is A II and III

When a person moves from lower to higher altitudes, the affinity of $O_2$ (i.e. $p_{O_2})$ and total atmospheric pressure decrease. Hypoxia will also increase the breathing rate. Hypoxia stimulates the JG-cells of the kidney to release the erythropoietin hormone, which stimulates erythropoiesis in bone marrow causing polycythemia (increased production of RBCs). Initially, the size of RBCs will increase, but with an increase in the number of RBCs, the size of RBCs becomes normal.