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Acids are donors, while bases are acceptors of protons in solutions. Many various acids and bases are incorporated into organisms by everyday alimentation and cell metabolism, whi­le the output routes are the respiratory system, kidneys and gastrointestinal system. The concentration of free protons in the blood (expressed as pH value) is strictly regulated, as it has a great impact on cell metabolism. There are many ways in which organisms defend them­selves against harmful pH changes. The first line of defense is buffering, which takes place in both extra- and intracellular fluids; the second is regulation of elimination of acids and bases via the respiratory system (volatile acids) and kidneys (nonvolatile acids – sodium hydro­gen carbonate). Many parameters can be determined from blood and urine samples, which can help diagnose and monitor patient acid-base disorders. Important measurements of uri­ne include pH, urinary titrable acid and net acid excretion for blood pH, hydrogen carbonate concentration and partial pressure of carbon dioxide. For further analysis of metabolic aci­dosis, base excess, anion and osmolal gaps need to be determined. Acid-base disorders are divided into metabolic disorders with primary change in blood hydrogen carbonate concen­tration, and respiratory disorders with primary change in partial pressure of carbon dioxide. Acidosis causes a decrease in blood pH, while alkalosis causes an increase. The management of these disorders mainly consists of treatment of the underlying disease. In severe cases, it is also necessary to correct the pH status by adding acids or bases to the patient’s blood.