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The bicarbonate buffer system is an acid-base homeostatic mechanism involving the balance of carbonic acid (H 2 CO 3), bicarbonate ion (HCO − 3 ), and carbon dioxide (CO 2 ) in order to maintain pH in the blood and duodenum , among other tissues, to support proper metabolic function. [ 1 ]
With carbonic acid as the central intermediate species, bicarbonate – in conjunction with water, hydrogen ions, and carbon dioxide – forms this buffering system, which is maintained at the volatile equilibrium [3] required to provide prompt resistance to pH changes in both the acidic and basic directions.
The bicarbonate buffer, consisting of a mixture of carbonic acid (H 2 CO 3) and a bicarbonate (HCO − 3) salt in solution, is the most abundant buffer in the extracellular fluid, and it is also the buffer whose acid-to-base ratio can be changed very easily and rapidly. [15]
The bicarbonate buffer system regulates the ratio of carbonic acid to bicarbonate to be equal to 1:20, at which ratio the blood pH is 7.4 (as explained in the Henderson–Hasselbalch equation). A change in the plasma pH gives an acid–base imbalance. In acid–base homeostasis there are two mechanisms that can help regulate the pH.
Recall that the relationship represented in a Davenport diagram is a relationship between three variables: P CO 2, bicarbonate concentration and pH.Thus, Fig. 7 can be thought of as a topographical map—that is, a two-dimensional representation of a three-dimensional surface—where each isopleth indicates a different partial pressure or “altitude.”
The pH of a solution containing a buffering agent can only vary within a narrow range, regardless of what else may be present in the solution. In biological systems this is an essential condition for enzymes to function correctly. For example, in human blood a mixture of carbonic acid (H 2 CO 3) and bicarbonate (HCO −
The inorganic carbon species include carbon dioxide, carbonic acid, bicarbonate anion, and carbonate. [5] It is customary to express carbon dioxide and carbonic acid simultaneously as CO 2 *. C T is a key parameter when making measurements related to the pH of natural aqueous systems, [6] and carbon dioxide flux estimates.
Aqueous carbon dioxide reacts with water to form carbonic acid which is very unstable and will dissociate rapidly into hydronium and bicarbonate. Therefore, in seawater, dissolved inorganic carbon is commonly referred to as the collection of bicarbonate, carbonate ions, and dissolved carbon dioxide (CO 2, H 2 CO 3, HCO − 3, CO 2− 3).