The system of tubes that carries blood through the body is called the circulatory system and consists of the heart and the blood vessels that are connected to the heart. The heart is the power organ that propels the blood through the tubes by rhythmic diastole and contraction. The heart also has an endocrine function and the circulation is divided into pulmonary and body circulation. The left heart pushes blood back to the right heart through the body circulation; the right heart pushes blood back to the left heart through the pulmonary circulation. The realization of the blood transportation function depends on the circulatory function, which mainly transports fresh blood, rich in oxygen and high in nutrients, to the various organs of the body. Then the carbon dioxide and wastes generated by the various organs of the body, through the respiratory system and urinary system out of the body to realize the metabolism, to ensure the normal work and operation of the organs.