Which function is performed by the lymphatic system?

• A. Produces red blood cells
• B. Secretes digestive enzymes
• C. Filters urine
• D. Returns excess interstitial fluid to the blood

Answer: (D)

The lymphatic system mainly handles fluid balance in the body. As fluids seep out of capillaries into tissues, some of that interstitial fluid needs a way back into the bloodstream. Lymphatic vessels collect this fluid, transport it as lymph, and return it to the blood, helping maintain circulating blood volume and prevent tissue swelling. Lymph nodes along the way filter the lymph and help defend against invaders, and fats absorbed from the gut also travel through lymph. This is why returning excess interstitial fluid to the blood is the function described.

The other options belong to different systems: red blood cells are produced in bone marrow, digestive enzymes are secreted by glands such as the pancreas, and urine is filtered by the kidneys.