The function of the circulatory system is to transport nutrients and oxygen to cells and carry wastes away from cells to the organs responsible for eliminating them from the body.The heart is a muscular pump.when the heart contracts,it produces pressure on the blood in the circulatory system.This pressure pushes blood through the body.The body travels away from the heart in vessels called arteries. it returns to the heart through vessels called veins.To stop blood from flowing backwards,flexible flaps of tissue called valves are found throughout the circulatory system in the heart and veins.Arteries and veins in close contact with the organs and tissues of the body.The exchange of nutrients,wastes,oxygen and carbon dioxide occur between tissues and the blood through the walls of these small vessels.