Biological Systems MCAT Practice Exam

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When the blood pH is too high, what substance do the kidneys excrete?

  1. Hydrogen ions (H+)

  2. Bicarbonate (HCO3-)

  3. Carbon dioxide (CO2)

  4. Ammonia (NH3)

The correct answer is: Bicarbonate (HCO3-)

When the blood pH is too high, a condition known as alkalosis occurs. In response to elevated blood pH, the kidneys play an essential role in maintaining acid-base balance by excreting bicarbonate (HCO3-). Bicarbonate is a base, and by removing it from the bloodstream, the kidneys help lower the pH back to a more normal range. The process of excreting bicarbonate effectively reduces the buffering capacity of the blood, which helps to increase acidity and counteract the alkalotic condition. By balancing the concentrations of hydrogen ions (H+) and bicarbonate, the kidneys help to maintain homeostasis.

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