The circulatory system consists of the heart, blood, and blood vessels, which work together to circulate blood throughout the body. Blood contains plasma and corpuscles, including red blood cells, white blood cells, and platelets. Red blood cells contain hemoglobin and carry oxygen, while white blood cells provide immunity by destroying germs. Platelets help the blood to clot and stop bleeding. The circulatory system transports nutrients, oxygen, carbon dioxide, wastes, hormones, and more around the body, and defends against disease. Arteries carry blood away from the heart through thick muscular walls, while veins return blood to the heart via thin walls under lower pressure.