How do the lungs typically compensate for metabolic alkalosis?

• A. By increasing respiratory rate
• B. By decreasing respiratory rate
• C. By retaining hydrogen ions
• D. By exhaling excess carbon dioxide

Answer: (B)

In metabolic alkalosis, the body experiences an increase in blood pH due to a surplus of bicarbonate or a loss of hydrogen ions. To compensate for this elevated pH and restore acid-base balance, the lungs play a crucial role through the regulation of carbon dioxide levels.

The primary way lungs compensate in this scenario is by decreasing the respiratory rate. When the respiratory rate decreases, it allows carbon dioxide (CO2) to accumulate in the blood. CO2 reacts with water to form carbonic acid, and this process lowers the pH back toward normal. Thus, by reducing the rate of respiration, the body can increase the concentration of carbon dioxide, leading to a decrease in blood pH, which helps mitigate the effects of metabolic alkalosis.

For the other choices, increasing the respiratory rate would lead to excess removal of CO2, exacerbating the alkalosis rather than correcting it. The retention of hydrogen ions primarily occurs in renal compensation, not a function of the lungs. Lastly, exhaling excess carbon dioxide would also contribute to a higher pH, worsening metabolic alkalosis.

In summary, the lungs compensate for metabolic alkalosis by decreasing the respiratory rate, which helps to retain carbon dioxide and thereby correct the pH imbalance.