Humans inhabit a range of altitudes, from below sea level to high mountainous regions. Most of the world's population lives at low to moderate altitudes:
- Low Altitudes: Sea level to 1,500 meters (4,921 feet). Examples include coastal cities and most urban areas.
- Moderate Altitudes: 1,500 to 2,500 meters (4,921 to 8,202 feet). Examples include Mexico City (2,250 meters) and Addis Ababa (2,355 meters).
- High Altitudes: 2,500 to 3,500 meters (8,202 to 11,483 feet). Examples include La Paz, Bolivia (3,640 meters) and Lhasa, Tibet (3,650 meters).
- Very High Altitudes: Above 3,500 meters (11,483 feet). Examples include Potosí, Bolivia (4,090 meters) and the Khumbu region near Everest Base Camp in Nepal (5,364 meters).
Physiological Adaptations to Altitude
Blood Composition:
- Increased Red Blood Cells: Higher altitudes prompt the body to produce more red blood cells to enhance oxygen transport.
- Hemoglobin Concentration: Hemoglobin levels increase to improve the oxygen-carrying capacity of the blood.
- 2,3-Diphosphoglycerate (2,3-DPG): Levels of 2,3-DPG in red blood cells increase, facilitating the release of oxygen from hemoglobin to tissues.
Lung Capacity:
- Larger Lung Volume: Individuals living at high altitudes may develop larger lung volumes to maximize oxygen intake.
- Increased Ventilation: Breathing rates increase to enhance oxygen uptake and carbon dioxide expulsion.
Oxygen Levels:
- Hypoxia: Lower atmospheric pressure at high altitudes means less oxygen is available. The body compensates through increased breathing and red blood cell production.
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