<Ul> <Li> The inner cell mass, also known as the embryoblast, gives rise to the primitive endoderm and the epiblast . <Ul> <Li> The primitive endoderm develops into the amniotic sac which forms the fluid - filled cavity that the embryo resides in during pregnancy . </Li> <Li> The epiblast gives rise to the three germ layers of the developing embryo during gastrulation (endoderm, mesoderm, and ectoderm). </Li> </Ul> </Li> <Li> The trophoblast is a layer of cells forming the outer ring of the blastocyst that combines with the maternal endometrium to form the placenta . Trophoblast cells also secrete factors to make the blastocoel . <Ul> <Li> After implantation, cytotrophoblast is the inner layer of the trophoblast, composed of stem cells which give rise to cells comprising the chorionic villi, placenta, and syncytiotrophoblast . </Li> <Li> After implantation, syncytiotrophoblast is the outermost layer of the trophoblast . These cells secrete proteolytic enzymes to break down the endometrial extracellular matrix to allow for implantation of the blastocyst in the uterine wall . </Li> </Ul> </Li> </Ul> <Li> The inner cell mass, also known as the embryoblast, gives rise to the primitive endoderm and the epiblast . <Ul> <Li> The primitive endoderm develops into the amniotic sac which forms the fluid - filled cavity that the embryo resides in during pregnancy . </Li> <Li> The epiblast gives rise to the three germ layers of the developing embryo during gastrulation (endoderm, mesoderm, and ectoderm). </Li> </Ul> </Li> <Ul> <Li> The primitive endoderm develops into the amniotic sac which forms the fluid - filled cavity that the embryo resides in during pregnancy . </Li> <Li> The epiblast gives rise to the three germ layers of the developing embryo during gastrulation (endoderm, mesoderm, and ectoderm). </Li> </Ul> <Li> The primitive endoderm develops into the amniotic sac which forms the fluid - filled cavity that the embryo resides in during pregnancy . </Li>

The medical term meaning embedding of the zygote in the uterine lining is