Our bodies make adjustments at higher altitudes. They create more red blood cells to carry oxygen through our bloodstream, which pushes air into normally unused portions of the lungs and produces citrate synthase. Citrate synthase is an enzyme that helps the oxygen found in hemoglobin to make its way into body tissue.
High altitude also triggers an increase in our breathing, heartbeat and urination. Low air pressure and low humidity at high altitudes cause moisture from your lungs and skin to evaporate more quickly, and your body's increased exertion requires more water to remain hydrated.