DEGREE OF ACIDITY AND ALKALINITY: The acidity or alkalinity (basicity) of a solution is measured on a scale of values called pH (parts hydrogen). The values on the pH scale range from 0 to 14, with 0 indicating the most acidic level and 14 the most alkaline. A solution with a pH of 7 is neutral because it contains the same number of H ions and OH ions. Pure water has a pH of 7. A solution with a higher concentration of H ions than OH ions is an acidic solution with a pH below 7. An alkaline solution, therefore, has a higher concentration of OH ions than H ions and has a pH above 7.
DYNAMICS OF pH IN THE BODY: A change of one pH unit is a 10-fold change in H ion concentration. This means that a solution with a Ph of 4 has 10 times as many H ions as a solution with a pH of 5, and 100 times as many H ions as a solution with a pH of 6. For example, gastric juice has a pH of 1 and coffee has a pH of 5. This means that gastric juice has 10,000 times as many H ions as does coffee. Although coffee is acidic, it is a weak acid and does not have the corrosive effect of gastric juice, a strong acid. The cells and internal fluids of the human body have a pH close to neutral. The pH of intracellular fluid is around 6.8, and the normal pH range of blood is 7.35 to 7.45. Fluids such as gastric juice and urine are technically external fluids, because they are in body tracts that open to the environment. The pH of these fluids may be more strongly acidic or alkaline without harm to the body. The pH of blood, however, must be maintained within its very narrow, slightly alkaline range. A decrease of only one pH unit, which is 10 times as many H ions, would disrupt the chemical reactions of the blood and cause the death of the individual.
Normal metabolism tends to make body fluids more acidic, and this tendency to acidosis must be continually corrected. Normal pH of internal fluids is maintained by the kidneys, respiratory system, and buffer systems.
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1. LACTIC ACID
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