The circulatory system consists of three main parts: blood vessels, heart, and blood. The blood vessels include arteries, capillaries and veins that transport blood throughout the body. The heart has four chambers and pumps blood through the body in a continuous cycle. It circulates oxygenated blood from the lungs through the arteries and returns deoxygenated blood to the lungs through veins. The blood carries oxygen, nutrients, waste and defenses through this cardiovascular network.