Which organ is primarily responsible for filtering blood to produce urine?

• A. Heart
• B. Liver
• C. Kidney
• D. Lungs

Answer: (C)

The kidneys are responsible for filtering blood to form urine. Inside each kidney, nephrons do the work: blood is filtered in the glomerulus to create a filtrate that contains water, electrolytes, and waste. As this filtrate moves through the tubules, essential substances and most of the water are reabsorbed back into the bloodstream, while additional waste is secreted into the filtrate. The result is urine, a concentrated waste product ready for excretion.

The heart’s role is to pump blood, not to filter it into urine; the liver processes nutrients and detoxifies chemicals, and the lungs exchange gases. None of those organs forms urine the way the kidneys do.