Question

People living at sea level have around 5 million RBCs per cubic millimetre of their blood whereas those living at an altitude of 5,400 m have around 8 million. This is because at high altitude,

• A. People eat more nutritious food, therefore more RBCs are formed
• B. People get pollution free air to breath and more oxygen is available
• C. There is more UV radiation from sun which enhances RBCs production
• D. Atmospheric oxygen is less and hence more RBCs are needed to absorb the required amount of oxygen to survive.

Answer 1

The correct option is D

Atmospheric oxygen is less and hence more RBCs are needed to absorb the required amount of oxygen to survive.

At higher altitudes, the composition of air remains almost the same as at the sea level, but the density of the air gradually decreases. The number of red blood cells per unit volume is likely to be higher in a person living at high altitudes. This is in response to the air being less dense at higher altitudes. More number of red blood cells (more amount of haemoglobin) is needed to trap oxygen from the rarefied (less dense) air having low $p{O}_2$.