The main function of the heart and blood vessels is to transport oxygen and nutrients to the body tissues. This is needed to remove metabolic waste products such as carbon dioxide, nitrogenous wastes, and acids from tissues to the kidneys for elimination. The heart provides a pumping mechanism, and the blood vessels provide the transport system. The arterial system delivers the blood to the tissues, whereas the venous system returns the blood to the heart. The cardiovascular system works in an integrated fashion and has both intrinsic and extrinsic control mechanisms to accomplish its task.