It's this tube-like structure, which is made of many, many epithelial cells all directly adjacent to each other, is what separates the outside world from our internal bodies.

这些管状结构,也是由许许多多上皮细胞,互相连接而成的,它使体内和体外,区分开来

耶鲁公开课 - 生物医学工程探索课程节选

This tube, this hollow tube, which food passes through is made up of many, many epithelial cells which directly abut one another and would be a flat sheet except that it's rolled up into a tube.

这个管道,这个中空的管道,食物可以穿行其中,而它就是由许多许多上皮细胞构成的,上皮细胞一个连着一个,形成了一个平坦的细胞层,但实际上它们还在肠管中卷成管状

耶鲁公开课 - 生物医学工程探索课程节选