In a blood buffer system, such as the bicarbonate buffer system, the concentration of HCO3- (bicarbonate ion) is typically higher than the concentration of H2CO3 (carbonic acid) due to several factors.
Firstly, carbonic acid (H2CO3) ionizes partially in water to form bicarbonate ions (HCO3-) and hydrogen ions (H+). This equilibrium reaction is reversible, and the ionization of carbonic acid is incomplete.
However, the concentration of HCO3- is higher than that of H2CO3 in the blood buffer system because of the presence of an enzyme called carbonic anhydrase. Carbonic anhydrase catalyzes the rapid conversion of carbon dioxide (CO2) and water (H2O) to carbonic acid (H2CO3), which then dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+). This enzymatic reaction occurs quickly, maintaining a higher concentration of bicarbonate ions.
Additionally, the blood buffer system maintains a balance between carbon dioxide and bicarbonate ions to regulate blood pH. When there is an excess of carbon dioxide in the blood, it diffuses into red blood cells and reacts with water to form carbonic acid, which then dissociates into bicarbonate ions and hydrogen ions. This helps to decrease the concentration of carbon dioxide and maintain the blood pH within a narrow range.
In summary, the concentration of HCO3- is higher than that of H2CO3 in the blood buffer system due to the presence of carbonic anhydrase, which catalyzes the conversion of carbon dioxide to carbonic acid and bicarbonate ions. This mechanism helps maintain the acid-base balance and regulate blood pH.