Living at a higher elevation will cause an increase in hematocrit levels. WHY?

Question

Living at a higher elevation will cause an increase in hematocrit levels. WHY?

Answer 1

The juxta-glomerular (J-G) apparatus in the kidney, which is responsible for the release of erythropoietin (EPO), is sensitive to the oxygen level in your blood. At high elevations, the oxygen pressure is lower, this stimulates the J-G apparatus to produce EPO, which stimulates the production of red cells in the bone marrow. This property is used by athletes when they are going to do sport at high altitudes. They can either give themselves a blood transfusion to increase their red cell count (haematocrit) or they can inject EPO, which stimulates production of red cells.

Answer 2

The other question you asked is a little more difficult, so I'll take the time answering this to think on it.  The reason why higher elevations increase hematocrit levels is actually very simple.  Think about it - what changes at different elevations?  The oxygen concentration in the air.  Mountain climbers have to carry concentrated oxygen with them when they go climbing for that very reason.  So the way that a body adapts is to procure as much oxygen from the air as possible, becoming more efficient at absorption of the necessary gas.  The more red blood cells you have, the more hemoglobin in your body, and the more hemoglobin, the more bound iron.  Iron is the nutrient in our system that binds oxygen, so more of it leads to more absorption.