Explain how the cardiovascular system adapts to exercise at altitude (2500 m) over both short-term (24 - 48 hours) and long-term (3+ weeks) periods. (8 marks)
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Sample Answer
Initial responses – Increased ventilation rate and depth:
- The body immediately responds to lower oxygen partial pressure at altitude by increasing breathing rate and depth (hyperventilation) to maximize oxygen uptake in the lungs.
Short-term adaptations – increased heart rate and cardiac output:
- Heart rate increases to compensate for reduced oxygen availability, while cardiac output rises to maintain adequate oxygen delivery to tissues, typically seen within the first 24 – 48 hours at altitude.
Long-term adaptations – increased EPO production:
- The kidneys detect lower oxygen levels and increase production of erythropoietin (EPO), a hormone that stimulates red blood cell production in the bone marrow.
Increased red blood cell production and hemoglobin concentration:
- Over 3+ weeks, the bone marrow responds to elevated EPO levels by producing more red blood cells, leading to a 10 – 15% increase in total hemoglobin concentration.
Enhanced oxygen carrying capacity:
- The increased number of red blood cells and hemoglobin molecules significantly improves the blood’s ability to transport oxygen from the lungs to working muscles.
Improved capillarisation in muscle tissue:
- New capillaries develop within muscle tissue to enhance oxygen delivery and removal of waste products, though this adaptation typically takes several weeks to develop fully.
Discussion of oxygen partial pressure effects:
- The reduced partial pressure of oxygen at 2500m (approximately 75% of sea level) triggers these adaptations as the body attempts to maintain adequate tissue oxygenation despite the thinner air.
Sample Answer
Initial responses – Increased ventilation rate and depth:
- The body immediately responds to lower oxygen partial pressure at altitude by increasing breathing rate and depth (hyperventilation) to maximize oxygen uptake in the lungs.
Short-term adaptations – increased heart rate and cardiac output:
- Heart rate increases to compensate for reduced oxygen availability, while cardiac output rises to maintain adequate oxygen delivery to tissues, typically seen within the first 24-48 hours at altitude.
Long-term adaptations – increased EPO production:
- The kidneys detect lower oxygen levels and increase production of erythropoietin (EPO), a hormone that stimulates red blood cell production in the bone marrow.
Increased red blood cell production and hemoglobin concentration:
- Over 3+ weeks, the bone marrow responds to elevated EPO levels by producing more red blood cells, leading to a 10-15% increase in total hemoglobin concentration.
Enhanced oxygen carrying capacity:
- The increased number of red blood cells and hemoglobin molecules significantly improves the blood’s ability to transport oxygen from the lungs to working muscles.
Improved capillarisation in muscle tissue:
- New capillaries develop within muscle tissue to enhance oxygen delivery and removal of waste products, though this adaptation typically takes several weeks to develop fully.
Discussion of oxygen partial pressure effects:
- The reduced partial pressure of oxygen at 2500m (approximately 75% of sea level) triggers these adaptations as the body attempts to maintain adequate tissue oxygenation despite the thinner air.