How do kidneys help control pH?

The kidneys play a crucial role in maintaining the body’s acid-base balance by regulating the levels of hydrogen ions and bicarbonate in the blood. The correct answer highlights that the kidneys control the ratio of hydrogen ions to bicarbonate excretion, which is essential for regulating pH levels.

In the process of maintaining pH, when the body is in an acidic state (with excess hydrogen ions), the kidneys can increase the excretion of these ions into the urine and retain bicarbonate, a base that helps neutralize acid. Conversely, when the blood is too alkaline, the kidneys can decrease hydrogen ion excretion and excrete more bicarbonate. This precise control over hydrogen ions and bicarbonate allows the kidneys to effectively manage the balance of acids and bases, thereby maintaining the normal physiological pH range of 7.35 to 7.45.

The other options do not adequately describe the kidneys' role in pH regulation. For instance, excreting sodium and calcium is more related to electrolyte balance rather than direct pH control. Carbon dioxide and carbonic acid regulation primarily occurs in the lungs, not through renal mechanisms. Lastly, while NADPH is involved in various metabolic processes, it does not play a direct role in pH balance within