Circulation is provided by the cardiovascular system, including both the heart and the blood vessels. There are three major categories of blood vessels:
-The arteries (number 1) transport oxygen and nutrients to tissues.
-The veins (number 2), convey the wastes from the tissues.
-Capillaries: Only the capillaries are in close contact with the cells and allow exchanges between the blood and the interstitial fluid that bathes the cells (nutrients, gases and wastes).
