Buffer systems are the body's first line of defense against extreme changes in H+ concentration. Recall the bicarbonate (HCO3-)/carbonic acid (H2CO3) system. It is the most important buffer system in the plasma.
In this reaction, carbon dioxide (CO2) reacts with water (H2O) to form carbonic acid (H2CO3), and then rapidly dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). The reaction is catalyzed by carbonic anhydrase.
In our bodies, this reaction is constantly occurring to maintain an acid/base balance.
CO2 + H2O <--> H2CO3 <--> HCO3- + H+
There are several reasons the bicarbonate/carbonic acid system is so important in our bodies:
- The dissociation of H2CO3 into CO2 and H2O allows for CO2 to be eliminated by the lungs and H+ as water.
- The respiratory rate is modified by changes in CO2.
- The kidneys can change the HCO3- concentration.
Therefore, the body's pH is balanced by a weak acid (H2CO3) and its base (HCO3-), so any excess acid or base added to the system is neutralized. This occurs via the lungs and kidneys.
