Anion-Cation Excretion: Acid-Base Balance

Abstract

Textbooks always contain a chapter entitled acid-base balance (e.g. Chapter 11 in Pitts, 1974) and there are reviews also under similar titles (e.g. Cogan, Rector and Seldin, 1981; Schwartz and Cohen, 1978). It is a somewhat misleading title to the experiments discussed in this chapter. The main argument can be stated by reference to Table 2, p. 3. S and P contained in the food are converted in the body to H₂SO₄ and H₃PO₄ and in man and dog excreted in the urine as anions, SO₄— and HPO₄—; with Cl- these are most of the anion in the urine (Table 1, p. 2). Cations contained in food are Na+ and K+ but in all foods except green vegetables and fruit, SO₄— + HPO₄— + Cl- exceeds Na+ + K+ (Lennon, Lemann and Litzow, 1966). The cation which fills the gap in the urine is NH₄+ and a small amount of hydrion buffered as H₂PO₄-. In man and dog excretion of NH₄+ in acid urine is essential to maintaining anion-cation equilibrium.