Which system eliminates nitrogenous wastes and regulates water, electrolyte and acid-base balance?

• A. Urinary system
• B. Digestive system
• C. Respiratory system
• D. Cardiovascular system

Answer: (A)

The system that eliminates nitrogenous wastes and regulates water, electrolyte, and acid-base balance is the urinary system. The kidneys filter blood to remove nitrogenous wastes such as urea, uric acid, and creatinine, forming urine that exits the body. They also control how much water you keep by concentrating or diluting urine, and they balance electrolytes (like sodium, potassium, and calcium) through selective reabsorption and secretion in the tubules. This same process manages acid-base balance by adjusting hydrogen ion and bicarbonate handling, helping keep blood pH within a narrow range. Other systems don’t perform this combination of waste elimination and homeostatic regulation: the digestive system mainly processes nutrients and expels indigestible material, the respiratory system mainly removes CO2 to influence pH, and the cardiovascular system transports wastes but does not excrete them.