Why can oral sodium bicarbonate tablets alkalize urine?
Orally administered sodium bicarbonate enters the stomach, right? Common sense tells us that the orally taken sodium bicarbonate should be neutralized by gastric acid (hydrochloric acid) into H2O, NaCl, and CO2, so how does it get into the urine and alkalize it? (I don’t have much education, please don’t mislead me).
Of course, our common sense is correct: oral sodium bicarbonate is indeed neutralized by gastric acid. But when HCO3- is neutralized by H+ in gastric acid, H+ in the body is consumed. We know that the body’s pH is maintained in a dynamic balance. When H+ in the body is consumed, it inevitably triggers corresponding “mobilization” by the body. This process involves two enzymes that play very important roles in maintaining the body’s acid-base balance: carbonic anhydrase and glutaminase.
(1) The main function of carbonic anhydrase: Carbonic anhydrase is mainly distributed in the proximal tubules and catalyzes the reaction CO2 + H2O to form H2CO3; H2CO3 then partially dissociates into H+ and HCO3-. Under normal circumstances, almost all the HCO3- filtered by the glomerulus is reabsorbed in the renal tubules and collecting ducts in the form of CO2, accompanied by H+ secretion (hydrogen ion secretion).
So, the keywords for the main role of carbonic anhydrase are: promote hydrogen secretion and promote HCO3- reabsorption.
(2) The main function of glutaminase: Glutaminase is mainly distributed in the proximal convoluted tubules and collecting ducts, where it catalyzes the deamination of glutamine to produce glutamate (which is further acted upon by glutamate dehydrogenase to form α-ketoglutarate and NH4+) and NH4+. NH4+ is then secreted into the tubular fluid via H-Na transport and finally excreted. NH4+ secretion also promotes HCO3- reabsorption.
Thus, the keywords for the main role of glutaminase are: promote NH4+ excretion and promote HCO3- reabsorption.
Therefore, when taking oral sodium bicarbonate, due to the consumption of H+, the body, in order to maintain acid-base balance, reduces H+ and NH4+ secretion and excretion in the kidneys and decreases HCO3- reabsorption. This ultimately results in an increase in urine pH (alkalization of urine).
References
More
According to this principle, if one frequently consumes acidic vinegar, wouldn’t it acidify the urine?