Blood circulation Blood circulation:circulation system is made up of the heart and vessels in which blood is flowing in certain direction ,going round and begin again. 血液循环：心脏和血管组成机体的循环系统，血 液在其中按一定方向流动，周而复始。 Cardiac structureBlood circulation: circulation system is made up of the heart and vessels in which blood is flowing in certain direction ,going round and begin again. 血液循环：心脏和血管组成机体的循环系统，血 液在其中按一定方向流动，周而复始。 Blood circulation Cardiac structure