In response to an acid-base disturbance, which condition leads to increased excretion of HCO3 by the kidneys to lower pH?

Increased excretion of HCO3 by the kidneys primarily occurs in the context of respiratory alkalosis. This condition arises when there is a decrease in carbon dioxide (CO2) levels in the blood, usually due to hyperventilation. As CO2 levels drop, the pH of the blood rises, leading to a state of alkalosis.

To compensate for this increased alkalinity, the kidneys respond by excreting bicarbonate (HCO3), which is a base. By excreting HCO3, the kidneys help bring the pH back down towards the normal range. This process involves reabsorption adjustments and the manipulation of bicarbonate levels in the urine, reducing the overall bicarbonate concentration in the blood and thus contributing to a decrease in pH.

In respiratory acidosis, the situation is the opposite. The body retains bicarbonate rather than excreting it, in response to elevated CO2 levels. Metabolic acidosis involves an increase in acid or loss of bicarbonate where the kidneys would typically retain bicarbonate to help correct the pH. In metabolic alkalosis, the kidneys might excrete bicarbonate to help adjust the higher pH, but the context is not about lowering pH in response to a primary