A patient comes to the emergency room after passing out. The doctor discovers a very low amount of salts in the body. The doctor should suspect problems with the patient's __________.

The kidneys help regulate the body's levels of salts and water by controlling what is kept in the blood and what is removed in urine. A very low salt level can therefore point to a kidney-regulation problem. The correct choice is “kidneys because the salts are not properly regulated”; the bladder stores urine but does not regulate salt levels.

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