Why do residents of highlands have more red blood cells per unit of blood volume than residents of plains?

In the mountainous regions, the air is more rarefied, with a reduced oxygen content, therefore, for normal oxygen supply of tissues, a larger number of red blood cells is required.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.