What is the functional unit of the kidney?

• A. Renal corpuscle
• B. Cortex
• C. Glomerulus
• D. Nephron

Answer: (D)

The nephron is the functional unit of the kidney. It carries out the complete process of urine formation: filtration at the renal corpuscle (which includes the glomerulus within Bowman's capsule), followed by selective reabsorption and secretion along the renal tubules (proximal tubule, loop of Henle, distal tubule) and final concentration in the collecting duct. The glomerulus and renal corpuscle are essential components, but they are only parts of a nephron—while the cortex houses many nephrons, the cortex itself is not the functional unit. Thus, the nephron—the whole filtering and processing unit—is what enables the kidney to regulate body fluids and waste.