The circulatory system includes the heart, blood vessels, and blood. The heart is a muscular pump made of four chambers that pumps blood throughout the body. There are three types of blood vessels - arteries, which carry blood away from the heart; capillaries, where nutrient and gas exchange occurs; and veins, which carry blood back to the heart. Blood contains red blood cells to carry oxygen, white blood cells for immunity, platelets for clotting, and plasma. The circulatory system transports these components between tissues and organs.