来自《耶鲁大学开放课程：生物医学工程探索 第13集 第13集》

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  This pattern repeats itself.
  血流按照如此模式循环往复
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  A pattern of flow, branch, branch, branch to ever smaller branches
  即通过不断产生分支 分支 更小的分支
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  so that you can serve ever smaller regions of tissue.
  来使血液能进入到组织中较小的部位
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  Now, these vessels that carry oxygenated blood are called arteries
  携氧血液流过的血管称为动脉
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  and they have thick muscular walls.
  动脉血管的管壁很厚
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  They're generally large diameter, a centimeter or so,
  直径也通常较大 有一厘米左右
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  there's a table in your book
  课本上有一个表
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  that gives you the diameters of different kinds of vessels.
  给出了各种血管的直径
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  They don't exchange materials with their outside environment.
  它们不与外界环境进行物质交换
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  You can think of these as conduits whose function
  这些动脉可以想象为一些水管
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  is to carry blood from the heart to a particular organ,
  其作用就是把血液由心脏送往特定器官
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  but not to exchange nutrients, not to exchange oxygen,
  但不进行营养和氧气交换