In acid-base balance, how does the carbonic acid (bicarbonate) buffer system help maintain blood pH?

• A. It reversibly converts between carbonic acid and bicarbonate to buffer added acids or bases (e.g., $H_2{C}_0{3}_{\mathrm{}}\rightleftharpoons H++H_0{C}_0{3}_{\mathrm{}}$, conceptually)
• B. It permanently removes $H+$ by converting it into glucose through glycolysis
• C. It maintains blood pH by binding oxygen more tightly to hemoglobin, preventing $H+$ release
• D. It raises blood pH primarily by increasing secretion of hydrochloric acid in the stomach

Answer: (A)

Verified step by step guidance

1. Understand that the carbonic acid-bicarbonate buffer system helps maintain blood pH by balancing the concentration of hydrogen ions (H\+), which directly affect acidity.
2. Recognize the reversible chemical reaction involved: carbonic acid (H\_2CO\_3) dissociates into bicarbonate (HCO\_3\-) and hydrogen ions (H\+), and vice versa. This can be written as: \(\text{H\_2CO\_3} \leftrightarrow \text{H\+} + \text{HCO\_3\-}\)
3. When excess acid (H\+) is added to the blood, bicarbonate ions (HCO\_3\-) bind with these hydrogen ions to form carbonic acid (H\_2CO\_3), reducing free H\+ concentration and minimizing pH change.
4. Conversely, when a base is added and H\+ concentration drops, carbonic acid dissociates to release H\+ ions, thereby preventing the pH from rising too much.
5. This dynamic equilibrium allows the buffer system to resist changes in blood pH by either consuming or releasing hydrogen ions as needed, maintaining acid-base homeostasis.