Site of action of furosemide is:-
**Core Concept**
Furosemide is a loop diuretic that acts on the renal tubules to increase urine production, thereby reducing fluid volume and blood pressure. The primary site of action of furosemide is in the thick ascending limb of the loop of Henle, where it inhibits the sodium-potassium-chloride cotransporter (NKCC2).
**Why the Correct Answer is Right**
Furosemide binds to the NKCC2 transporter, which is responsible for reabsorbing sodium, potassium, and chloride ions in the thick ascending limb of the loop of Henle. By inhibiting this transporter, furosemide prevents the reabsorption of these ions, leading to an increase in the delivery of sodium and chloride to the distal tubules and collecting ducts. This results in increased excretion of water, sodium, and chloride in the urine. The inhibition of NKCC2 also leads to secondary effects on other transporters in the renal tubules, further increasing the excretion of potassium and magnesium.
**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect, as furosemide does not primarily act on the proximal convoluted tubule, which is the site of action of carbonic anhydrase inhibitors.
* **Option B:** Incorrect, as furosemide does not primarily act on the distal convoluted tubule, which is the site of action of potassium-sparing diuretics.
* **Option C:** Incorrect, as furosemide does not primarily act on the collecting ducts, which are the site of action of aldosterone antagonists.
**Clinical Pearl / High-Yield Fact**
Furosemide is a potent diuretic, but its use can lead to hypokalemia, hypomagnesemia, and metabolic alkalosis due to the increased excretion of potassium and magnesium.
**Correct Answer:** C. Thick ascending limb of the loop of Henle