Which components comprise the bicarbonate buffer system used to regulate pH in the blood?

• A. Potassium and chloride
• B. Oxygen and carbon dioxide
• C. CO2 and bicarbonate
• D. Sodium and bicarbonate

Answer: (C)

The bicarbonate buffer system relies on a weak acid–conjugate base pair formed from dissolved carbon dioxide and bicarbonate. In the blood, CO2 produced by metabolism combines with water to form carbonic acid, which quickly dissociates into hydrogen ions and bicarbonate. The pH is kept within a narrow range by the ratio of [HCO3−] to dissolved CO2 (often described using the Henderson–Hasselbalch relationship). The lungs influence this system by adjusting CO2 levels through breathing, while the kidneys regulate bicarbonate reabsorption and generation. This dynamic balance allows the blood to resist pH changes.

The correct pair is CO2 and bicarbonate because they are the components that directly form and buffer the carbonic acid–bicarbonate system. Other options involve ions or gases that participate in different processes (electrolyte balance or gas exchange) but are not the buffering partners in this system.