Q: Gastric fluid itself contains very little potassium (about 10 mEq/L) than why vomitting induces hypokalemia?


Answer: Vomitting induce volume depletion which causes hypokalemia by 3 systemic effects.

1. Volume depletion leads to secondary hyperaldosteronism, which, in turn, causes enhanced cortical collecting tubule secretion of potassium in response to enhanced sodium reabsorption.

2. Metabolic alkalosis which increases collecting tubule potassium secretion due to the decreased availability of hydrogen ions for secretion in response to sodium reabsorption.

3. Metabolic alkalosis directly enhances potassium entry into cells.