What is the function of the human excretory (renal) system?

• A. It digests fats
• B. It filters the blood
• C. It stores minerals
• D. It produces hormones

Answer: (B)

The main idea is that the renal system filters the blood and forms urine to remove waste while keeping the body's fluids and electrolytes in balance. The kidneys act on blood to remove waste products like urea, excess water, and salts, and they adjust how much water and minerals are reabsorbed, helping maintain pH and overall homeostasis. They also contribute to hormone production, such as erythropoietin and renin, and activate vitamin D, but these roles support the filtration and regulation they perform. The other options don’t fit because fat digestion happens in the digestive system, minerals aren’t stored by the kidneys, and while the kidneys do produce some hormones, the primary function described here is filtration and excretion.