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The study of kidney function on the regulation of the acid-base state
Last reviewed: 18.10.2021
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Maintaining CBS with maintaining a stable pH of the arterial blood is carried out by homeostatic mechanisms, which are based on the physico-chemical properties of blood and tissues, as well as physiological processes occurring in the lungs, kidneys, liver and gastrointestinal tract (GI tract).
In clinical practice, urine pH, ammonia secretion, secretion of titrated acids, and excretion of bicarbonates are used to assess the ability of the kidneys to maintain CBS.
In a healthy person, the pH of the urine under normal conditions fluctuates between 4.5 and 7.5, often shifting to low values (in the acidic side). Overloading meat food contributes to the release of more acidic urine, while vegetable diet, abundant alkaline drink significantly increase the pH of urine.
Excretion of titrated acids characterizes the amount of secreted hydrogen ions associated with anions of phosphates and weak organic acids. It is determined by titrating urine with a solution of alkali to the pH of the blood.
Normally, the excretion of titrated acids is 10-30 mmol / day, or 7-21 μmol / min; excretion of bicarbonates - 1-2 mmol / day; the secretion of ammonia is 30-60 mmol / day (21-35 μmol / min).
Ammonia, when bound to hydrogen, promotes the excretion of strong acid anions (in the form of ammonium salts). Anions of weak acids are released in the form of titrated acids. Total kidney excretion of acids - total excretion of H + - is 40-90 mmol / day.
The limit of excretion of acids is the level of titration acidity and excretion of ammonia, at which the pH of urine reaches 4.5. When urine pH is below 6.0, i.e. In conditions of complete reabsorption of bicarbonates, the total excretion of hydrogen ions is the sum of the daily excretion of ammonium and titrated acids.