Which statement best describes the antihypertensive effect of diuretics?

• A. Promote sodium and water loss
• B. Increase potassium retention
• C. Reduce renal filtration
• D. Increase heart rate

Answer: (C)

The main concept is that diuretics lower blood pressure by reducing extracellular fluid volume through increased excretion of sodium and water. By blocking reabsorption of sodium in parts of the nephron, diuretics cause more Na+ and water to be wasted in the urine. The resulting volume depletion lowers venous return and cardiac output, which lowers blood pressure. Over time, this volume reduction can also contribute to lower peripheral vascular resistance. This mechanism is distinct from reducing renal filtration rate; diuretics do not primarily act by lowering GFR. They also do not inherently raise heart rate as their main effect. The impact on potassium depends on the class: some diuretics cause potassium loss, while potassium-sparing agents preserve or increase it.