The rapid acting chemical buffers combine with the acids or bases entering the body fluids to prevent drastic changes in the H⁺ concentration and the pH.  These buffers combine with the strong acids replacing them with weaker acids, and vice versa.  The buffers don’t actually rid the body of H⁺ or CO₂ but combine with them until another system can excrete (rid) them from the body.  Chemical buffer reactions are reversible depending on whether an acid or base state exists.  A strong acid easily dissociates (breaks up) freeing up more hydrogen ions.  As a result of the buffer’s action a weak acid that contributes fewer hydrogen ions replaces a strong acid with the potential to contribute many hydrogen ions and the pH is lowered only slightly (fewer H⁺) instead of dramatically (more H⁺).  

The major chemical buffers include:

a.      carbonic acid (H₂CO₃)

b.      bicarbonate (HCO₃)

c.      plasma proteins and phosphates.

Normal extracellular fluid has a ratio of 1:20—carbonic acid to bicarbonate.  This means for every 1 part of carbonic acid there must be 20 parts of bicarbonate.  This ratio of acid to base is critical.  The exact quantity of each component is unimportant; what is important is the 1:20 ratio.  When this 1:20 ratio is maintained acid-base balance remains near normal despite changes in the absolute amounts of either the carbonic acid or bicarbonate buffer. 

Carbonic acid can dissociate into bicarbonate and hydrogen—or—into water and carbon dioxide depending on whether an acid or base state exists, thereby maintaining the 1:20 ratio and preserving the body’s pH at @ 7.4.  A change in the ratio in either direction (increase or decrease) will affect the pH—either increasing it (alkalosis) or decreasing it (acidosis).  The body’s ability to regulate the amount of either/both component(s) to maintain the correct ratio for acid-base balance makes this system one of the most important for controlling the pH of body fluids.

The principles of buffering action (as illustrated by the carbonic acid-bicarbonate buffers) can be applied equally to the plasma proteins and phosphate buffers.  They are powerful buffers and are capable of functioning as either an acid or base depending on the existing acidity/alkalinity of body fluids.  They are active in the plasma as well as in the intracellular and extracellular fluids. 

Plasma proteins are the most plentiful buffers in the body working both inside and outside the cells.  Of the plasma proteins, albumin occurs in the highest concentration and has the greatest buffering capacity.  Other plasma proteins (e.g. immunoglobulins, hemoglobin) are present but in lower concentrations and are less physiologically active.  Like the carbonic acid-bicarbonate buffer system, the plasma proteins bind with acids and bases to weaken or neutralize them.

The phosphate buffers are active in the intracellular fluids rather than in the extracellular fluids.  They also react with either acids or bases forming compounds that result in only slight shifts in the body’s pH, again proving to be an especially effective buffering mechanism.  Even so, phosphates are the least important of the major non-bicarbonate buffers in the extracellular fluid due to their low concentration levels.  In fact, the buffering capability of phosphates in the extracellular fluid is only slightly greater than that of hemoglobin.