What is the functional unit of the kidney?

• A. Glomerulus
• B. Renal pelvis
• C. Nephron
• D. Ureter

Answer: (C)

The nephron is the kidney’s functional unit. It carries out filtration, reabsorption, and secretion to transform blood into urine. Filtration happens in the glomerulus, a tiny capillary tuft inside Bowman's capsule, creating a filtrate that then passes through the tubule system (proximal tubule, loop of Henle, distal tubule, and collecting duct). Along these tubules, most water and useful solutes are reabsorbed back into the blood, while wastes and excess ions are secreted into the tubule for excretion. The collecting ducts drain into the renal pelvis and then into the ureter. The renal pelvis and ureter are pathways for urine, not sites that form it, so the nephron best fits as the functional unit responsible for urine formation.