Which statement about loop diuretics is true?

Which statement about loop diuretics is true?

• A. They act on the distal tubule to promote potassium retention
• B. They are never used for edema
• C. They are not potent
• D. They act on the loop of Henle and cause loss of potassium, calcium, and magnesium

Answer: (D)

Loop diuretics work by inhibiting the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle. This blocks reabsorption of Na+, K+, and Cl-, producing a powerful diuresis. Because this transporter helps create a lumen-positive potential that drives paracellular reabsorption of calcium and magnesium, blocking it increases their excretion as well. The increased delivery of sodium to the distal nephron also promotes potassium secretion, leading to potassium loss. These drugs are among the most potent diuretics and are commonly used to treat edema, and they act specifically at the loop of Henle rather than the distal tubule.