Which best describes the primary function of the kidney?

• A. Filters blood and produces urine
• B. Stores urine
• C. Produces red blood cells
• D. Regulates body temperature

Answer: (A)

The kidneys’ main job is to filter the blood and form urine so waste products are removed and fluid, electrolyte, and acid-base balance are maintained. This happens in the nephrons, where blood is filtered in the glomerulus, the filtrate is then reabsorbed or secreted along the tubules, and the final urine is collected and excreted. This filtering-and-forming-urine process is what lets the body clear wastes like urea and creatinine while keeping necessary substances in balance. The other options point to functions of other organs or to secondary roles: storing urine is the bladder’s job, erythropoietin from the kidneys can influence red blood cell production but is not the kidney’s primary function, and regulating body temperature is not a primary renal role.