These cells around the outside form the interface, the placenta, where the maternal blood circulation meets the embryonic circulation and nutrients are passed back and forth that way in a very highly regulated and important way.

外层的细胞形成接触面,即胎盘,是母血与胎血,进行血液交换,及营养物质交换的场所,整个过程高度有序并且非常重要

耶鲁公开课 - 生物医学工程探索课程节选