Which description best captures the primary functions of the kidneys?

• A. They regulate oxygen transport in the blood
• B. They filter waste, regulate fluids and electrolytes, and maintain acid-base balance
• C. They control heart rate
• D. They coordinate muscle movement

Answer: (B)

The kidneys’ main job is to keep the body's internal environment stable by filtering waste from the blood, balancing fluids and electrolytes, and maintaining acid-base balance. Nephrons filter blood to remove waste products like urea and creatinine, while reabsorbing needed substances and concentrating urine. They finely adjust fluid volume and electrolyte levels (such as sodium, potassium, and bicarbonate) to keep blood chemistry in balance. They also regulate pH by reclaiming bicarbonate and excreting hydrogen ions, helping keep blood pH within a narrow, healthy range. Other choices describe functions for the heart, lungs, or muscles, which are not roles of the kidneys.