The first line of defense in acid-base regulation is:
A. a decrease in the ventilation-perfusion ratio B. the chemical buffers C. a decrease in the ventilatory equivalent D. renal regulation of H+
The correct answer and explanation is:
The correct answer is B. the chemical buffers.
Explanation:
The first line of defense in acid-base regulation is the use of chemical buffers, which are systems that resist changes in pH by neutralizing excess acids or bases. These buffers operate within seconds to prevent drastic changes in blood pH. The main chemical buffer systems in the body include the bicarbonate buffer system, the protein buffer system, and the phosphate buffer system.
- Bicarbonate buffer system: This is the most significant buffer in the extracellular fluid. It works by balancing carbonic acid (H2CO3) and bicarbonate (HCO3−) in a reversible reaction. When there is an excess of hydrogen ions (H+), bicarbonate combines with them to form carbonic acid, which can then be converted to carbon dioxide (CO2) and exhaled. When there is a shortage of hydrogen ions, carbonic acid dissociates to release H+, raising the pH.
- Protein buffer system: Proteins, especially hemoglobin in red blood cells, can bind to free hydrogen ions. Proteins have amino acid groups that can act as weak acids or bases, helping to stabilize pH. The protein buffer system is especially important in intracellular fluid.
- Phosphate buffer system: The phosphate buffer works similarly to the bicarbonate system but in a slightly different pH range. It is important in the kidneys and intracellular fluids, where phosphate concentrations are higher. This system also involves a weak acid (H2PO4−) and a weak base (HPO4^2−), which can neutralize excess H+ or OH−.
The effectiveness of chemical buffers lies in their ability to act immediately to stabilize the body’s pH. If the buffering systems cannot compensate for an acid-base imbalance, the second and third lines of defense are employed: respiratory regulation of CO2 (ventilation adjustments) and renal regulation of hydrogen ions (through the kidneys), respectively. These mechanisms take longer to respond but are critical for long-term regulation of acid-base balance.