Which part of the nephron does the diuretic Furosemide primarily target?

Which part of the nephron does the diuretic Furosemide primarily target?

• A. Ascending loop of Henle
• B. Descending limb of Henle
• C. Proximal tubule
• D. Collecting duct

Answer: (A)

Furosemide is a loop diuretic, and its primary action is at the thick segment of the ascending limb of the loop of Henle. There it inhibits the Na+/K+/2Cl− cotransporter (NKCC2), which normally reabsorbs a large portion of filtered sodium, potassium, and chloride from the tubular fluid. By blocking this transporter, furosemide prevents reabsorption of these ions, leading to increased excretion of Na+, Cl−, water, and also calcium and magnesium. This site is key because the ascending limb actively dilutes the tubular fluid and helps create the medullary concentration gradient; blocking reabsorption here disrupts that gradient and promotes diuresis. The other nephron segments play different roles. The descending limb mainly reabsorbs water and is not a target for loop diuretics. The proximal tubule reabsorbs most solutes and water early in the nephron and is not the primary site of loop diuretics. The collecting duct handles final water reabsorption and is where other diuretics (like those acting on the distal tubule or aldosterone pathways) exert effects, not the loop diuretics.

Furosemide is a loop diuretic, and its primary action is at the thick segment of the ascending limb of the loop of Henle. There it inhibits the Na+/K+/2Cl− cotransporter (NKCC2), which normally reabsorbs a large portion of filtered sodium, potassium, and chloride from the tubular fluid. By blocking this transporter, furosemide prevents reabsorption of these ions, leading to increased excretion of Na+, Cl−, water, and also calcium and magnesium. This site is key because the ascending limb actively dilutes the tubular fluid and helps create the medullary concentration gradient; blocking reabsorption here disrupts that gradient and promotes diuresis.

The other nephron segments play different roles. The descending limb mainly reabsorbs water and is not a target for loop diuretics. The proximal tubule reabsorbs most solutes and water early in the nephron and is not the primary site of loop diuretics. The collecting duct handles final water reabsorption and is where other diuretics (like those acting on the distal tubule or aldosterone pathways) exert effects, not the loop diuretics.