The apoptotic bodies distributed in all layers of the epithelial cells in the esophagus, but mainly located near the free surface of epithelium in the intestines.

食管上皮中凋亡小体分布于上皮各层，而肠上皮中主要在上皮游离面。

youdao

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