Hydrochlorothiazide (HCTZ) primarily targets which nephron segment?

Hydrochlorothiazide (HCTZ) primarily targets which nephron segment?

• A. Proximal tubule
• B. Distal convoluted tubule
• C. Loop of Henle
• D. Collecting duct

Answer: (B)

The main concept tested here is where a thiazide diuretic acts along the nephron. Hydrochlorothiazide inhibits the Na+-Cl- cotransporter in the early part of the distal convoluted tubule, reducing Na and Cl reabsorption at that site and increasing their excretion with water. This makes the distal convoluted tubule the correct target, unlike the proximal tubule (where many other diuretics act, or where bulk reabsorption occurs), the loop of Henle’s thick ascending limb (targeted by loop diuretics that block NKCC2), or the collecting duct (targeted by potassium-sparing diuretics). An additional effect of thiazides is a small increase in calcium reabsorption, which can be clinically relevant.

The main concept tested here is where a thiazide diuretic acts along the nephron. Hydrochlorothiazide inhibits the Na+-Cl- cotransporter in the early part of the distal convoluted tubule, reducing Na and Cl reabsorption at that site and increasing their excretion with water. This makes the distal convoluted tubule the correct target, unlike the proximal tubule (where many other diuretics act, or where bulk reabsorption occurs), the loop of Henle’s thick ascending limb (targeted by loop diuretics that block NKCC2), or the collecting duct (targeted by potassium-sparing diuretics). An additional effect of thiazides is a small increase in calcium reabsorption, which can be clinically relevant.