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Title: Describe the events of embryonic development from conception until the fetal sta Post by: colleen on Oct 4, 2013 Describe the events of embryonic development from conception until the fetal stage, including development of the primary germ layers.
Title: Re: Describe the events of embryonic development from conception until the fetal sta Post by: padre on Oct 8, 2013 A fertilized egg ( zygote) undergoes rapid mitotic cell division in a stage called cleavage. Cleavage provides the building blocks for constructing the embryo, which develops until it has about 100 cells and then hollows out to form a blastocyst. The blastocyst has two areas: the trophoblast and the inner cell mass. The inner cell mass forms the primary germ layers, which are the ectoderm, the endoderm, and the mesoderm. The ectoderm gives rise to the nervous system, the epidermis, and the skin. The endoderm forms the mucosae and associated glands. The mesoderm gives rise to everything else. The trophoblast develops projections called chorionic villi which form the placenta along with tissues from the mother's uterus. By the eighth week, all the organ systems have been laid down and the embryo looks distinctly human. Beginning in the ninth week, the embryo is referred to as a fetus.
Title: Re: Describe the events of embryonic development from conception until the fetal sta Post by: jackie614 on Oct 8, 2013 thank u :)
Title: Re: Describe the events of embryonic development from conception until the fetal sta Post by: padre on Oct 8, 2013 |