The circulatory system which we'll talk about in a couple of weeks, the heart, the blood vessels, and the blood work together to form a totally internal function.

例如过几周我们要讲的循环系统,心脏,血管,血液,三者协同工作,形成一个完全在体内发挥作用的体系

耶鲁公开课 - 生物医学工程探索课程节选

Internal refers to the transformation, the changing of the form.

内在是指转变，形态的改变。

哈佛公开课 - 幸福课课程节选