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The body requires oxygen to carry on the process of life. A network of arteries and veins transport oxygen-rich blood to the body and return oxygen-poor blood to the lungs. At the center of this continuous process is the heart, a beating muscle about the size of your fist.The heart pumps approximately five quarts of blood every minute, and each heartbeat circulates blood to both the lungs and the body. This is possible because of the heart's complex internal structure.
机体在生命过程中需要氧气。动静脉网把富含氧气的血液运送到机体，将乏氧血液运送到肺。这个连续过程在中心是和你的拳头一样大小的跳动肌肉——心脏。心脏每分钟泵出大约5夸脱的血液，每次心跳使机体和肺内的血液循环。这个过程得以进行是因为心脏内部复杂的结构。
The heart is divided into the right side and the left side. The right side comprises the right atrium and right ventricle; these chambers collect oxygen-poor blood and pump it to the lungs, where oxygen is replenished. The left side of the heart comprises the left atrium and left ventricle; these chambers collect and pump the oxygen-rich blood to the body.
心脏被分为左部和右部。右部由右心房和右心室组成，这两个腔将乏氧血液泵入肺，在肺内氧重新得到补充。左部由左心房和左心室组成，这两个腔收集富含氧气的血液并将其泵入机体。
