Acidity and Alkalinity
For the purpose of enzyme activity and to maintain the shape and structure of the proteins, the body must maintain the right state of acidity and alkalinity. If there are more H+(hydrogen ions), a solution is acidic. If there are more OH- (hydroxyl ions), the so-lution is alkaline. The acidity and alkalinity of a solu-tion is measured in terms of pH (hydrogen ion con-centration). As the quantity of hydrogen ion is so small, it is cumbersome to express in actual numbers. If needed, the number would be something like 0.0000001. To make it easier, this is expressed by pH. The pH is actually a measure of hydrogen ion con-centration in the body fluid; the pH scale extends from 0 to 14. Water is considered to be a pH of 7.0; a neutral pH. This means that water contains 0.0000001, or 1 Œ 10-7 of a mole of hydrogen ions per liter. If the pH is lower than 7.0, it denotes that the fluid has more hydrogen ions or that it is acidic. For example, if a solution has a pH of 5.0, it contains 0.00001 or 1 Œ 10-5 of a mole of hydrogen ions per liter (i.e., more hydrogen ions than a solution of pH 7.0). If a solution has a pH above 7.0, it has less hy-drogen ions than water and is alkaline.
The pH of the body is 7.4 (range, 7.35–7.45) (i.e., slightly alkaline). For body enzymes to be active and for chemical reactions to proceed optimally, it is vital that pH be maintained at this level. This implies that the body needs regulatory mechanisms that monitor the hydrogen ion levels carefully and get rid of them as and when they form above normal levels.
One of the body’s compensatory mechanisms is the presence of many buffers. Buffers are compounds that prevent the hydrogen ion concentration from fluctuating too much and too rapidly to alter the pH. The body uses buffers to convert strong acids (that dissociate easily into hydrogen ions) to weak acids (that dissociate less easily). Proteins, hemoglobin, and a combination of bicarbonate and carbonic acid compounds are a few of the buffers present in body fluids. The later is an important buffer. The following chemical reaction indicates how a combination of bi-carbonate and carbonic acid compounds work as buffers.
HCO3- + H → H2CO3 → H2O CO2
In this chemical reaction, HCO3 (bicarbonate), a weak base, combines with the hydrogen ions to form H2CO3 (carbonic acid), a weak acid. This weak acid can be further broken down to CO2 (carbon dioxide), which can be breathed out, and H2O (water), which can be used for other reactions or excreted by the kid-neys. Alternately, if the pH becomes acidic, the weak carbonic acid H2CO3 can break down to form HCO3-(a weak base) and H+(hydrogen ions).