What balance do the kidneys maintain?

• A. Oxygen transport and cellular respiration
• B. Reabsorption of nutrients in the small intestine
• C. Maintenance of water, electrolyte and acids/base balance
• D. Immune function in the lymphatic system

Answer: (C)

The kidneys regulate water, electrolyte levels, and the body's acid-base status. They filter the blood, then selectively reabsorb what the body needs (such as water and essential ions) and excrete what’s in excess as urine. This control over fluid volume and osmolarity, together with precise handling of ions like sodium, potassium, and bicarbonate, keeps electrolyte balance stable. They also manage pH by reabsorbing bicarbonate and secreting hydrogen ions, adjusting urine composition to maintain blood pH around 7.35–7.45. Hormones like ADH and aldosterone fine-tune these processes, shaping water reabsorption and ion balance in response to the body’s needs. That coordination is what maintains overall fluid, electrolyte, and acid-base balance. The other options point to functions handled by different systems (oxygen transport by the blood, nutrient absorption by the GI tract, immune work by the lymphatic system).