Integrated use of the expressions and partial sentences you learnt from the text by translation ______1______(循环系统或心血管系统) is___________2______(封闭的器官和血管) that_____3________(将血液输送到全身). The primary purposes of the circulatory system are to deliver nutrients, immune factorsand oxygen to tissues and to carry away___4_______(废物) for elimination. The heart is a four-chambered pump that propels the blood throughout the body.____5________(贫氧的血液) enters _______6_____(右心房) through_______7_____(上腔和下腔静脉) after returning from the body. The blood next_________8_________(经三尖瓣进入右心室). When the heart contracts, the blood from the right ventricle is pumped_____9________(经肺动脉至肺). There, _____10_______(血液充氧) at the alveoli and returns to the heart through the pulmonary veins. The oxygenated blood is received at the left atrium and proceeds____11_______(经二尖瓣至左心室). When the heart contracts, the oxygenated blood is pumped throughout the body via a series of_______12___(血管) called arteries. The first and largest artery is called the ____13_____. The arteries sequentially branch and decrease in size (and are called arterioles) until they end in a network of smaller vessels called capillaries. The capillary beds are located in the ¬¬_____14______(胞间隙) within tissues and release nutrients, immune factors, and oxygen to those tissues. _____15__________(其他器官在循环系统中也起着重要作用). ____16__________(淋巴系统)is also a network of vessels that____17______(遍布全身). However, these vessels do not form a full circulating system and are not pressurized by the heart. Rather, the lymphatic system is an___18______(开放系统)with the fluid ____19_________(向同一方向流动) from the extremities toward two drainage points into veins just above the heart. _______20__________(淋巴液比血液流动慢) because they are not pressurized. Small lymph capillaries interact with blood capillaries in the interstitial spaces in tissues. Fluids from the tissues enter the lymph capillaries and are drained away. These fluids, termed lymph, also contain large numbers of white blood cells.