Which statement best describes the kidney's role in acid-base balance during prolonged exercise?

Which statement best describes the kidney's role in acid-base balance during prolonged exercise?

• A. It regulates potassium balance during prolonged exercise.
• B. It increases hepatic lactate production to buffer pH.
• C. It elevates bicarbonate synthesis in plasma.
• D. It regulates bicarbonate reabsorption and hydrogen ion excretion to maintain pH during lactate-induced acidosis.

Answer: (D)

During prolonged exercise, lactic acid from muscles lowers blood pH, so the kidneys work to restore acid-base balance by handling bicarbonate and hydrogen ions. The key action is reabsorbing bicarbonate from the filtrate back into the blood and excreting hydrogen ions into the urine, which helps neutralize excess acidity and maintain pH despite lactate buildup. The kidneys can also generate new bicarbonate over time, but the essential response in lactate-induced acidosis is reclaiming bicarbonate and bumping up H+ excretion to offset the acidosis.

Other options miss this combined kidney role. Potassium balance is important for several reasons, but it isn’t the main mechanism of acid-base correction during prolonged exercise. Liver lactate production doesn’t buffer pH; the liver actually helps clear lactate, not buffer it, and buffering is primarily a bicarbonate-related process. Simply increasing bicarbonate synthesis doesn’t capture the core renal response of reclaiming bicarbonate and excreting hydrogen ions to maintain pH.