Which is described as the second vital buffer in the blood, acting as the principal buffer of red blood cells?

• A. Hemoglobin
• B. Bicarbonate
• C. Plasma proteins
• D. Phosphate buffer system

Answer: (A)

Hemoglobin inside red blood cells acts as the primary buffer there. As CO2 from tissues diffuses into RBCs, it’s converted to carbonic acid and then to bicarbonate and H+. The hydrogen ions would lower pH, but deoxygenated hemoglobin binds these H+ ions at its histidine residues, helping to keep the intracellular pH stable. This buffering by hemoglobin is key for maintaining the pH environment inside red blood cells and supports CO2 transport. In contrast, the bicarbonate system is the main buffer of plasma outside the cells, while plasma proteins and the phosphate system provide additional, smaller buffering roles in various compartments.