人体内组织不断地进行着新陈代谢,从血液中摄取氧和各种营养,同时将二氧化碳和废物释出于血液之中。接受二氧化碳和废物的血液聚集于大静脉,返回心脏(废物在返回途中,被肾脏过滤得干干净净)。心脏具有“唧筒”样的作用,集中干大静脉的血液,被心脏的左右心室 Organizations in the body are constantly metabolizing, taking in oxygen and various nutrients from the blood while releasing carbon dioxide and waste into the blood stream. The blood that receives carbon dioxide and waste accumulates in the large veins and returns to the heart (the waste is filtered clean on the way back by the kidneys). The heart has a “pump” -like effect, focus on the blood of the dry large vein, the heart’s left ventricle