the cardiovascular system is composed of the heart and blood vessels
heart is a hollow muscular organ lying in the mediastinum
mediastinum is the center of the thoracic cavity between the lungs
the pumping action of the heart propels blood containing oxygen, nutrients, and other vital products to body cells through a vast network of blood vessels called arteries
blood returns to the heart through blood vessels called veins
on its return trip to the heart, blood picks up waste products from the body cells to deliver them to the organs of excretion
trillions of body cells rely on the cardiovascular system for survival
when the transportation system fails, life at the cellular level is not possible and, ultimately, the organism will die
