Which organ contains the nephron as its functional unit?

• A. Liver
• B. Kidney
• C. Spleen
• D. Pancreas

Answer: (B)

Nephrons are the workhorse units that filter blood and reabsorb or secrete substances to form urine, so the organ that contains them is the kidney. A kidney houses millions of nephrons, each with a glomerulus for filtration and a tubular system (proximal tubule, loop of Henle, distal tubule, collecting duct) that reclaims water and ions and adjusts urine composition, ultimately concentrating urine as needed. This arrangement lets the kidney regulate fluid and electrolyte balance, remove waste, and maintain acid-base homeostasis. Other organs listed have different specializations and units—liver with hepatic lobules, spleen with its immune and filtering roles, and pancreas with acini and islets—so they don’t contain nephrons. So the organ that contains the nephron as its functional unit is the kidney.