Which two of the following changes (i – iv) usually tend to occur in the plain dwellers when they move to high altitudes (3,500 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
- (ii) and (iii)
- (iii) and (iv)
- (i) and (iv)
- (i) and (ii)
Answer
(1) (ii) and (iii)
Solution
At high altitude the partial pressure of O2 in air is low, so less oxygen reaches the tissues.
To take in more O2 the breathing rate increases (iii), and the kidneys release more erythropoietin, which increases RBC production in the bone marrow (ii) and raises the oxygen-carrying capacity of blood.
The size of RBCs and the count of thrombocytes (platelets) do not change for this purpose.
∴ Changes (ii) and (iii) occur.
Answer: (1)