A climber ascending to high altitude begins to breathe rapid

A climber ascending to high altitude begins to breathe rapid - HiSET Prep

Question

A climber ascending to high altitude begins to breathe rapidly, even though physical exertion is minimal. Which physiological explanation best accounts for this response?

Answers

correct

Reduced atmospheric pressure decreases oxygen availability, stimulating chemoreceptors to increase ventilation.
The respiratory center suppresses diaphragm activity to conserve oxygen at higher altitudes.
The alveoli expand excessively at low pressure, decreasing oxygen diffusion.
The kidneys immediately increase bicarbonate reabsorption, triggering faster breathing.

Explanation

Correct Answer: A. Reduced atmospheric pressure decreases oxygen availability, stimulating chemoreceptors to increase ventilation. At high altitude, atmospheric pressure is significantly lower, reducing the partial pressure of oxygen in the air. This means less oxygen diffuses into the bloodstream through the alveoli. Peripheral chemoreceptors in the carotid and aortic bodies sense the decline in arterial oxygen and send signals to the respiratory center in the medulla to increase breathing rate (hyperventilation). This compensatory mechanism enhances oxygen uptake and carbon dioxide removal. Over time, acclimatization occurs as the body increases red blood cell production and adjusts hemoglobin affinity for oxygen.

Why the Other Options Are Incorrect:

B. The respiratory center suppresses diaphragm activity to conserve oxygen at higher altitudes.
Suppressing diaphragm activity would reduce ventilation and worsen oxygen deprivation. The respiratory center instead increases respiratory drive to maintain oxygenation.
C. The alveoli expand excessively at low pressure, decreasing oxygen diffusion.
Alveoli do not overexpand at altitude; the limiting factor is reduced oxygen partial pressure, not excessive alveolar size.
D. The kidneys immediately increase bicarbonate reabsorption, triggering faster breathing.
Bicarbonate regulation is a delayed renal response to pH changes, not an immediate respiratory stimulus. Breathing rate changes occur first, driven by chemoreceptor activity.