Which organ is primarily responsible for filtering blood and producing urine?

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

Answer: (B)

Filtering blood and producing urine is the function of the kidneys. Each kidney contains nephrons, the tiny filtering units that remove waste products and excess substances from the blood, then reabsorb what the body needs and secrete additional wastes into the forming urine. This urine collects and exits the body, while the process helps regulate fluid balance, electrolyte levels, and acid-base balance, and even influences blood pressure through hormonal signaling. The other organs serve different roles: the liver processes nutrients and toxins, the heart pumps blood, and the spleen helps filter blood and support immunity. So the kidneys are the organ most directly responsible for filtering blood and producing urine.