There's no point where the circulatory system crosses the boundary between being inside you and outside of you, it's totally internal.

循环系统绝不会,跨越人体的内外界限,它完全位于体内

耶鲁公开课 - 生物医学工程探索课程节选

The respiratory system plays an important role in maintaining our internal environment at the proper level of oxygen, by bringing the right amount in.

呼吸系统的重要性在于,通过向体内输入适量的氧气,维持人体内环境中的氧平衡

耶鲁公开课 - 生物医学工程探索课程节选

This is the internal pressure of the system.

这是内部压强。

麻省理工公开课 - 热力学与动力学课程节选

Depending on what you call external and internal environment, this path that I'm tracing here, deep within your digestive system, is really directly connected to the outside world through both ends.

基于你们所谓的外环境和内环境,我在这里我所指的消化系统内部通路,它的两端确实与外界环境直接相通

耶鲁公开课 - 生物医学工程探索课程节选