Circulatory system consists of heart and blood vessels. Consider heart as a pump and blood vessels as tubewells or channels. Blood vessels include arteries, veins and capillaries. Heart pumps fresh blood in arteries from where this blood is used by different body organs. The used blood that is impure blood is then carried from various organs by veins back to the heart. Capillaries are the small blood vessels which connect arteries with veins. Hope it clarifies your query.