Which statement about the renal system is true?

• A. It detoxifies poisons through the liver
• B. It controls voluntary muscle movement
• C. It regulates blood glucose via insulin
• D. It filters blood and produces urine to maintain fluid and electrolyte balance

Answer: (D)

The renal system maintains homeostasis by filtering blood and producing urine to regulate fluid volume and electrolyte balance. The kidneys receive blood, filter it through the glomeruli, reabsorb what the body needs, and excrete waste into urine. This filtering and urine formation establish and maintain the right balance of water and key ions such as sodium, potassium, calcium, and bicarbonate, keeping blood volume, osmolality, and pH within narrow limits. While the kidneys do contribute to blood pressure regulation and can influence red blood cell production and vitamin D activation, the statement that best captures their primary role is filtering blood and producing urine to maintain fluid and electrolyte balance. The other options point to functions of other organs: the liver detoxifies poisons, the nervous system controls voluntary movement, and the pancreas regulates blood glucose with insulin.