Circulation of blood: A = left atrium, B = left ventricle, C = right atrium, D = right ventricle, E = lungs, F = organs. 1 = aorta (artery), 2 = artery, 3 = capillaries, 4 = vein, 5 = inferior vena cava, 6 = superior vena cava, 7 = pulmonary artery, 8 = pulmonary vein, 9 = lymphatic vessel and lymph node.