Loop diuretics increase the excretion of which substances?

• A. Sodium and water only.
• B. Calcium and magnesium.
• C. Sodium, chloride, water, and potassium.
• D. Glucose and urea.

Answer: (C)

Loop diuretics block the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle. That transporter normally reabsorbs sodium, chloride, and potassium together, and its activity helps pull water out of the filtrate. When it’s inhibited, these ions stay in the tubular lumen, and water follows, leading to increased excretion of sodium, chloride, and water. The higher flow of sodium to the collecting duct also boosts potassium secretion, raising potassium loss in the urine. Additionally, blocking this transporter reduces the lumen-positive potential that helps reabsorb calcium and magnesium, so calcium and magnesium excretion goes up too. The strongest match for the typical diuretic effect is the loss of sodium, chloride, water, and potassium.