The system of tubes that carry blood through the body is called the circulatory system and consists of the heart and the blood vessels that connect to it. The heart is the power organ that drives blood through the tubes by rhythmic diastole and contraction. The heart also has an endocrine function, and the blood circulation is divided into pulmonary and somatic circulation. The left heart drives blood back to the right heart through the body circulation; the right heart drives blood back to the left heart through the pulmonary circulation. The fulfillment of the blood transport function is dependent on the circulatory function, which primarily transports fresh blood, rich in oxygen and high in nutrients, to the various organs of the body. Then the carbon dioxide and waste generated by each organ of the body are excreted through the respiratory and urinary systems to realize the metabolism and ensure the normal work and operation of the organs.