What is the function of the kidneys?

• A. They filter blood from the renal arteries and produce urine as waste
• B. They store bile
• C. They pump blood to lungs
• D. They break down carbohydrates

Answer: (A)

The kidneys mainly filter waste from the blood and produce urine. Blood enters through the renal arteries and is filtered in the nephrons, where waste products like urea and excess salts are pulled from the blood to form urine. At the same time, essential substances and most of the water are reabsorbed back into the bloodstream to maintain fluid and electrolyte balance, as well as blood pressure. The kidneys also help regulate acid-base balance, secrete certain ions, and release hormones such as erythropoietin and renin, plus activate vitamin D for calcium balance. Urine is then excreted from the body through the urinary tract. The other options describe functions of the liver/gallbladder, the heart, and the digestive system, which are not kidney functions.