The fifth only carried the green protein in its placenta tissue at birth.
VOA: special.2009.06.23
The cells of this surrounding sheet have become different in some way and they develop into the placenta and the extra embryonic tissues.
环抱在周围的这一层细胞,已经开始逐渐分化,最终成为胎盘,及额外的胚胎组织
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
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