The kidneys and sweat glands both work to prevent excesses of either uric acid or urine in the body. either water or salt in the body. either carbon dioxide or oxygen in the body. either feces or ph levels in the body.

Either water or salt in the body

Explanation:

Function of kidneys is to produce the concentration or dilute urine according to the hydration level of body as well as to maintain the electrolyte level (level of Na, K, calcium and bicarbonate ions) of blood.  Similarly, sweat glands serve to maintain the water-salt level of body by release of excess water and salt from the body in form of sweat.