What is the response of the lungs when serum pH is high or low?

The lungs play a crucial role in regulating acid-base balance in the body by controlling the levels of carbon dioxide (CO2) in the blood. When serum pH is high, indicating alkalosis, the body responds by retaining CO2 through slow and shallow breathing, which increases acidity and helps lower the pH back toward normal. Conversely, when serum pH is low, indicating acidosis, the lungs will increase the rate and depth of breathing (hyperventilation) to expel more CO2. This loss of CO2 decreases the concentration of carbonic acid in the blood, leading to an increase in pH.

This rapid adjustment of CO2 levels is a key function of the respiratory system, enabling the body to respond swiftly to changes in pH, unlike bicarbonate (HCO3-) levels, which are adjusted more slowly by the kidneys. Thus, the main response of the lungs to changes in serum pH is to quickly adjust the CO2 levels in the blood, thereby helping to maintain homeostasis.