The Cardiovascular System
The cardiovascular system and the lymphatic system form what is collectively called the circulatory system. Together, these systems transport oxygen, nutrients, cell wastes, hormones, and many other substances to and from all cells in the body. The trillions of cells in the human body take up nutrients and excrete wastes every minute of every day. Although the pace of this exchange may increase with activity or slow with rest, it happens continuously. If it stops, so does life. Of the two systems, the cardiovascular system is the primary transport operator; the lymphatic system aids it in its function.