Substantial quantities of inorganic and organic acids are generated from the dissolving of metabolically produced CO2 in water, and the metabolism of sulfur-containing amino acids and phosphorus-containing compounds. Lactic acid and ketoacids (acetoacetate and hydroxybutyrate) are also produced. The excess of lactic acid is the hallmark of hypoxic conditions and the accumulation of ketoacids becomes clinically important in diabetes (see Chapter 20). Acids derived from sources other than CO2 are known as nonvolatile; by definition, they cannot be removed through the lungs, and must be excreted via the kidney. The net production of nonvolatile acids is in the order of 50 mmol/24 h.
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| Blood and tissues contain buffer systems to minimize changes in hydrogen ion concentration
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| These systems are summarized in Table 23.1 (see also Chapter 2). The main buffer that neutralizes hydrogen ions released from cells is bicarbonate. Hemoglobin also plays an important role in buffering hydrogen generated from the carbonic anhydrase reaction (see below). Hydrogen ion is also buffered by intracellular buffers, mainly proteins and phosphates.
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