The hydrogencarbonate system

This system is unusual in that it consists of only tlie salt sodium hydrogencarbonate, a weak base, which is also is the salt of the weak carbonic acid. In solution, sodium hydrogencarbonate readily dissociates into ions  

If there is an excess of free hydrogen ions in the body, they are immediately taken up by the hydrogencarbonate ions, to form weak carbonic acid which has no ill effects. 

If the alkalinity of the system is increased, hydrogencarbonate ions can react with free hydroxide ions to form carbonate ions and water. 

This system helps to ensure that the pH of body fluids is never drastically altered. However, although in the body sodium hydrogencarbonate acts as a buffer on its own, it plays a relatively minor role as a buffer, and in most cases two or more substances are involved, as in inorganic systems. Phosphate salts play a more important role in regulating hydrogen ion concentration in the blood. 

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In this system the weak acid is sodium dihydrogenphosphate (NaH2P04) and the weak base is disodium hydrogenphosphate (Na2HP04). The action of the buffer system is similar to that of the hydrogencarbonate system. 

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