在羊膜动物胚胎学，哺乳动物的上胚层是从内细胞团中所分化的组织；鸟类、爬虫类则是从胚盘所发育出来的。位于下胚层的上方。

在哺乳动物胚胎学，当下胚层的立方细胞逐渐靠近囊胚细胞；上胚层的柱状细胞与滋胚层细胞相连接， 上胚层与被称为第一外胚层，因为可以发展成之后的外胚层、中胚层、内胚层等三个胚层。这三个胚层之后会与原肠形成发育相关联。

上胚层多样性

人类上胚层是盘状构造，老鼠的上胚层则是杯状形状。

In amniote animal embryology, the epiblast is one of two distinct layers arising from the inner cell mass in the mammalian blastocyst or from the blastodisc in reptiles and birds. It derives the embryo proper through its differentiation into the three primary germ layers, ectoderm, mesoderm and endoderm, during gastrulation. The amnionic ectoderm and extraembryonic mesoderm also originate from the epiblast.