Acid-base balance, ammonia metabolism

Excretion into urine of ammonia produced by renal mbu-lar cells facilitates cation conservation and regulation of acid-base balance. Ammonia production from intracellular renal amino acids, especially glutamine, increases in metabolic acidosis and decreases in metabolic alkalosis. 

A description of acid-base balance involves an accounting of the carbonic (H2C03, HCOh COa", and CO2) and noncar-bonic acids and conjugate bases in terms of input (intake plus metabolic production) and output (excretion plus metabolic conversion) over a given time interval. The acid-base status of the body fluids is typically assessed by measurements of total CO2 plasma pH and PCO2, because the bicarbonate/carbonic acid system is the most important buffering system of the plasma. Occasionally, measurement of total titratable acid or base, or other acid and base analytes (e.g., lactate and ammonia [NH3]) is necessary to determine the etiology of an acid-base disorder. 

As a metabolic organ, the K. is responsible for the constancy of the acid-base balance of the body. The normal pH of the blood is 7.4, and it is important that this value is not increased (see Alkalosis) or decreased (see Acidosis). The K. contains amine oxidases and glutaminase, which catalyse the production of free ammonia. In acidosis these reactions are brought into play and excess H ions are consumed by formation of NH In addition to the natural secretory processes foreign substances such as pharma-... 

In normal subjects, protein-rich diets do not cause a rise in the blood urea level but the blood urea level does tend to rise with age and causes a corresponding increase of the level in the saliva. Urea is an important substrate for bacterial metabolism and is converted into ammonia which plays a part in regulating the acid-base balance within the plaque (page 505). This could be a contributory factor in the higher incidence of periodontal disease in older subjects. 

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