Dr Sevag Demirjian, director of Critical Care Nephrology at Cleveland Clinic, reviews the mechanism of action of furosemide (Lasix) in the kidney. He describes the nephron (basic functional unit of human kidney), and how through a series of channels, furosemide is first secreted in the proximal renal tubular epithelial cells then travels to block the sodium, potassium chloride symporter in the ascending loop of Henle.