Anatomy and Physiology II Practice Test

Which substance is identified as a buffer in the body?

1. Lemon juice

2. Aldosterone

3. Antidiuretic hormone

4. Bicarbonate

The correct answer is: Bicarbonate

Bicarbonate is recognized as a vital buffer in the body due to its role in maintaining pH balance in the bloodstream and other bodily fluids. It participates in the bicarbonate buffer system, which involves the equilibrium between bicarbonate ions (HCO₃⁻) and carbonic acid (H₂CO₃). When hydrogen ions are released into the solution, bicarbonate can neutralize them to form carbonic acid, thereby preventing significant fluctuations in pH. This buffering action is crucial, as the human body operates optimally within a narrow pH range of about 7.35 to 7.45. In contrast, the other substances listed do not serve the primary function of buffering. Lemon juice is acidic and can lower pH rather than stabilize it. Aldosterone is a hormone that regulates sodium and potassium balance, impacting blood pressure and fluid balance without a significant buffering role. Antidiuretic hormone primarily helps control water retention and influences urine concentration, again lacking the buffering capacity provided by bicarbonate. Thus, bicarbonate stands out as the key buffering agent that helps maintain the body's acid-base homeostasis.