# Nonvolatile acid

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{{Short description|Physiological category of acids}}
A '''nonvolatile acid''' (also known as a '''fixed acid''' or '''metabolic acid''') is an [acid](/source/acid) produced in the body from sources other than [carbon dioxide](/source/carbon_dioxide), and is not excreted by the lungs.  They can be produced from an incomplete metabolism of carbohydrates, fats, and proteins.  All acids produced in the body are nonvolatile except [carbonic acid](/source/carbonic_acid), which is the sole [volatile acid](/source/volatile_acid).  Common nonvolatile acids in humans are [lactic acid](/source/lactic_acid), [phosphoric acid](/source/phosphoric_acid), [sulfuric acid](/source/sulfuric_acid), [acetoacetic acid](/source/acetoacetic_acid), and [beta-hydroxybutyric acid](/source/beta-hydroxybutyric_acid).  Humans produce about 1–1.5 mmoles of H<sup>+</sup> per kilogram per day.<ref>{{cite web| url= http://www.anaesthesiamcq.com/AcidBaseBook/ab2_1.php | title= Acid-Base Physiology | access-date= 2007-05-30}}</ref>  Most nonvolatile acids are excreted by the [kidney](/source/kidney)s. Lactic acid is usually completely metabolized by the body, and is thus not excreted from the body.

==Reactions==
The following reactions result in nonvolatile acids:

* [sulfur](/source/sulfur)-containing amino acid [oxidation](/source/oxidation)s:<ref name=boron846>{{cite book |author=Walter F., PhD. Boron |title=Medical Physiology: A Cellular And Molecular Approach |publisher=Elsevier/Saunders |isbn=1-4160-2328-3 }} Page 846</ref>
*:e.g. [methionine](/source/methionine) or [cysteine](/source/cysteine) → [urea](/source/urea) + CO<sub>2</sub> + H<sub>2</sub>SO<sub>4</sub> → 2H<sup>+</sup> + {{chem|SO|4|2−}}
* [phosphorus](/source/phosphorus)-containing compound metabolism<ref name=boron846/> → H<sub>3</sub>PO<sub>4</sub> → H<sup>+</sup> + {{chem|H|2|PO|4|−}}
* cationic amino acid oxidation:<ref name=boron846/>
*: e.g. [lysine](/source/lysine) or [arginine](/source/arginine) → urea + CO<sub>2</sub> + H<sub>2</sub>O + H<sup>+</sup>
* Non-metabolizable organic acid production:<ref name=boron846/>
*: HA → H<sup>+</sup> + A<sup>−</sup>
* Incomplete metabolism of carbohydrates, fats, and proteins<ref name=boron846/> → e.g. [lactic acid](/source/lactic_acid) or [keto-acid](/source/keto-acid)s

==See also==
*[Carbonic acid](/source/Carbonic_acid)
*[Volatile acid](/source/Volatile_acid)

==References==
{{reflist}}

Category:Acid–base physiology

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