The bicarbonate buffering system is an important buffer system in the acid-base homeostasis of living things, including humans. As a buffer, it tends to maintain a relatively constant plasma pH and counteract any force that would alter it.
In this system, carbon dioxide (CO2) combines with water to form carbonic acid (H2CO3), which in turn rapidly dissociates to form hydrogen ion and bicarbonate (HCO3- ) according to the reaction below. The reverse (leftward) reaction is catalyzed by the enzyme carbonic anhydrase.
Any disturbance of the system will be compensated by a shift in the chemical equilibrium according to Le Chatelier's principle. For example, if the blood gained excess hydrogen ions (a process called acidosis), some of those hydrogen ions would shift to carbon dioxide, minimizing the increased acidity. This buffering system becomes an even more powerful regulator of acid-base homeostasis when it is coupled with the body's capacity for respiratory compensation, in which breathing is altered to modify the amount of CO2 in circulation. In the above example, the body could increase breathing (respiratory alkalosis) to expel the excess CO2, pulling still more hydrogen ions toward the production of carbon dioxide. The process could continue until the excess acid is all exhaled.
This process is extremely important in human physiology. It manages the many acid and base imbalances that can be produced by both normal and abnormal physiology. It also affects the handling of carbon dioxide as it is constantly produced as a waste product of cellular respiration when cells make energy.
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