What Happens to the Body When You Change Altitudes?

The human body is perfectly adapted to life at sea level, but it must adapt to survive at higher altitudes. Physiological changes, which kick in as low as 5,000 feet, are due to decreased atmospheric pressure and their purpose is to increase the amount of oxygen and the efficiency with which it is delivered to the cells. Some physiological changes kick in immediately, while others occur over a period of weeks. The higher the altitude, the harder the body has to work to stay alive.

  1. Respiratory Rate

    • One of the earliest physiological changes, increased respiratory rate and depth, occur in the body within hours of reaching a high altitude due to lower concentrations of oxygen in the blood. Breathing more frequently and more deeply allows the lungs to absorb more oxygen and release more carbon dioxide, leading to a process known as hyperventilation. Normally, after about a week at the higher altitude, respiratory rate decreases as other physiological changes help the body absorb oxygen.

    Kidney Excretion

    • The increased respiratory rate and resulting hyperventilation leads to the body becoming more alkaline. To make the body more acidic, the kidneys begin to secrete bicarbonate in the urine. The kidneys are responsible for filtering the blood and removing wastes, which are then excreted in urine. Having the kidneys excrete alkaline bicarbonate in the urine is the body's way of restoring pH balance.

    Heart Rate

    • At higher altitudes, the heart beats faster and certain non-essential bodily functions, such as food digestion, are stopped or reduced to allow the body to focus more energy on increasing oxygen concentrations. After a period of time at the same altitude, the heart rate usually returns to normal. Increased heart rate is also an immediate adaptation to higher elevations.


    • Hematopoiesis is the scientific term applied to the production of red blood cells. At high elevations, hematopoiesis is increased, leading to increased red blood cell concentration in the blood. This change happens within four to five days of living at a higher altitude. Its purpose is to increase the blood's capacity to carry oxygen. A person typically has 30 to 50 percent more red blood cells, once they acclimate to a certain altitude, than they did at sea level.


    • Capillaries are the smallest blood vessels in the body. They allow the exchange of oxygen, carbon dioxide, nutrients and wastes between the blood and surrounding tissues. At higher altitudes, the body forms more capillaries in skeletal muscle to allow more oxygen to reach the tissue.

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