When a person ascends a mountain, what physiological change occurs in their blood due to increased breathing rate?

When a person ascends a mountain, the reduced atmospheric pressure at higher altitudes leads to lower availability of oxygen. To compensate for this, the body responds by increasing the breathing rate, which enhances the uptake of oxygen. This increased respiration rate can lead to a higher exhalation of carbon dioxide (CO2) from the body.

As CO2 is expelled, the level of bicarbonate (HCO3-) in the blood decreases, which results in a shift in the carbonic acid-bicarbonate buffering system. This shift causes the pH of the blood to increase, leading to a more alkaline state, referred to as respiratory alkalosis. Therefore, the correct answer indicates that the increase in breathing rate during ascent contributes to an increased pH of blood, as the body adapts to the lower oxygen availability by maintaining appropriate acid-base balance.

Understanding these physiological changes is crucial for recognizing how the body adapts to varying environmental conditions, especially in scenarios like high-altitude climbing where oxygen levels are considerably lower.