physical stressors pt.2

High Altitude Adaptation Overview

  • Definition: High altitude defined as elevation > ~2,500 m (8,000 ft); affects ~140 million people.

  • Physiological effects noticeable in human settlements up to 5,000 m (16,000 ft).

Environmental Stressors

  • Factors: UV radiation, cold, arid conditions, low soil quality, hypoxia (reduced oxygen availability).

  • Oxygen Concentration: Remains at 21%, but fewer molecules per volume due to low pressure.

Biological Responses to Hypoxia

  • Responses: Increased breathing rate (hyperventilation), increased heart rate, and RBC production (erythropoietin).

  • Consequences: Risk of respiratory alkalosis; potential increased viscosity of blood (polycythemia).

Adaptation Mechanisms

  • Capillary Adjustments: Increased active capillaries in the lungs and pulmonary blood flow regulation.

  • Acclimatization: Enhances oxygen delivery, increasing BMR, ventilation rates, RBC count, and capillarization.

Health Risks from High Altitude

  • Acute Mountain Sickness (AMS): Symptoms include nausea, headache, and insomnia.

  • High Altitude Cerebral Edema (HACE): Symptoms include confusion and ataxia.

  • High Altitude Pulmonary Edema (HAPE): Symptoms include chest tightness and cough.

Population-Specific Adaptations

  • Andeans: Short stature, increased lung volume, more RBCs and hemoglobin, lower reaction to hyperventilation.

  • Himalayans: Maintain typical hemoglobin levels and low Hb concentrations; adapt through high resting ventilation and nitric oxide presence.

  • Tibetan Adaptations: High capillary density, effective oxygen diffusion, and no pulmonary hypertension.

Genetic Diversity in Adaptations

  • Genetic Analysis: Identified candidate genes showing adaptation routes among populations; mixed phenotype expression seen between Himalayan and Andean populations.

Developmental Impacts

  • Growth Patterns: High-altitude residents show delayed growth; enhanced lung development.

  • Birth Weight: Typically lower for deliveries at high altitudes due to intrauterine growth restrictions.

Cultural Adaptations

  • Coca Leaf Usage: Widely practiced among Indigenous Andeans for heat retention and energy.

  • Nutritional Considerations: Consumption of vitamins and minerals such as calcium and iron may reduce AMS symptoms, though evidence remains unclear.