Which organ is part of the circulatory system?

• A. Lymph node
• B. Liver
• C. Heart
• D. Kidney

Answer: (C)

Understanding which organ functions as the central pump of the circulatory system helps explain why this organ is part of that system. The circulatory system moves blood through a network of vessels, delivering oxygen and nutrients and carrying away wastes. The heart is the muscular organ that contracts to push blood into the arteries and then receives it back through the veins, maintaining the circulation to lungs and to every tissue. That pumping action defines its role in the circulatory system. Other organs listed serve different systems: lymph nodes belong to the lymphatic system and help fight infection; the liver handles metabolism and bile production; the kidneys filter blood to form urine and regulate fluid balance, aligning with the urinary and metabolic roles rather than serving as the main pump of circulation.