The organ responsible for filtering metabolic waste from the bloodstream to form urine is the

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

Answer: (D)

The kidneys filter metabolic waste from the bloodstream to form urine. They do this through tiny filtering units called nephrons. In the nephron, blood is filtered at the glomerulus, allowing water and small solutes to enter the tubule. As this filtrate travels through the renal tubules, the body reabsorbs back into the blood what it needs, such as water and essential ions, while waste products like urea are concentrated into urine by secretion into the filtrate. The urine then travels to the collecting ducts and exits the body. This filtering and processing keep fluid balance, electrolyte levels, and waste removal in check. Other organs have different roles: the liver metabolizes many substances and helps detoxify the blood but doesn’t form urine; the spleen filters blood and supports immunity; the stomach digests food.