What is the mechanism of action of furosemide (Lasix) regarding diuresis?

Furosemide, commonly known as Lasix, is a loop diuretic that acts primarily at the ascending limb of the loop of Henle in the nephron. Its mechanism of action involves the inhibition of the Na+-K+-2Cl- symporter, which is responsible for the reabsorption of sodium, potassium, and chloride ions in this segment of the nephron. By blocking this symporter, furosemide prevents the reabsorption of these electrolytes, leading to an increase in the osmotic pressure within the tubular fluid. As a result, water follows these solutes through osmosis, leading to increased urine output or diuresis.

This mechanism explains its effectiveness in treating conditions such as heart failure, edema, and hypertension, where the goal is to reduce fluid overload. The choice indicating that furosemide acts at the ascending limb of the loop of Henle accurately captures its primary site of action and the physiological processes involved in fluid and electrolyte balance.