What are the two primary mechanisms by which the kidneys help maintain blood pH?

• A. Secretion of bicarbonate and reabsorption of hydrogen ions
• B. Reabsorption of sodium and secretion of potassium
• C. Secretion of sodium and reabsorption of potassium
• D. Reabsorption of bicarbonate and secretion of hydrogen ions

Answer: (D)

Verified step by step guidance

1. Understand that the kidneys play a crucial role in maintaining the acid-base balance in the body, which is essential for normal cellular functions.
2. Recognize that the kidneys help regulate blood pH by managing the levels of bicarbonate (HCO₃⁻) and hydrogen ions (H⁺) in the blood.
3. Identify that reabsorption of bicarbonate ions (HCO₃⁻) from the renal tubules back into the blood helps to neutralize excess acids, thus increasing blood pH.
4. Understand that secretion of hydrogen ions (H⁺) into the renal tubules for excretion in urine helps to remove excess acidity from the blood, thus maintaining a stable pH.
5. Conclude that the two primary mechanisms by which the kidneys maintain blood pH are the reabsorption of bicarbonate ions and the secretion of hydrogen ions.