What is the main driving force of the bicarbonate-carbonic acid buffering system?

• A. Oxygen
• B. Carbon Dioxide
• C. Carbon Monoxide
• D. Hydrogen Ion

Answer: (B)

The bicarbonate-carbonic acid buffer is governed by the amount of carbon dioxide in the blood. CO2 readily reacts with water to form carbonic acid, which dissociates to hydrogen ions and bicarbonate. The pH of the system is determined by the ratio of bicarbonate to dissolved CO2 (pH = pKa + log([HCO3-]/[CO2])), and in the body, [CO2] is set by how much CO2 is produced and how effectively it is ventilated away. Because ventilation can rapidly adjust CO2 levels, CO2 acts as the main driver in maintaining pH. Oxygen and carbon monoxide don’t participate in this buffering chemistry, and hydrogen ions are the product of the reaction, not the primary control. Therefore, carbon dioxide is the driving force.