来自《耶鲁大学开放课程：生物医学工程探索 第17集 第17集》

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  or just the movement of molecules down concentration gradients,
  或者说就是分子沿浓度梯度的运动规律
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  and it also happens by active transport.
  同样也包括主动运输
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  We talked about active transport earlier.
  我们前面说过主动运输了
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  We talked--for example when we were talking about the action potential,
  我们谈到 比如我们讲动作电位的时候
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  we talked about this active transport system
  谈到过其中的主动运输系统
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  that's able to shuttle sodium and potassium molecules across membranes.
  能够将钠和钾离子跨膜转运
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  So, most cells in the body have this active transport system
  身体内细胞大多都具有这种主动运输系统
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  called the sodium potassium pump, or the sodium potassium ATPase.
  称为钠钾泵 或者说钠钾ATP酶
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  Its main function is to bring sodium from inside the cell,
  它的主要功能是将钠从细胞内部
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  pump it out, take potassium from outside the cell and pump it in.
  泵到外部 并把钾从细胞外部泵进来
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  As a result of the action of this pump
  钠钾泵作用的结果
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  that's what creates this normal state that you have
  就是使得细胞处于正常状态