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Embryonic development
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Embryonic development is what happens to the embryo during its first eight weeks. In that time, a zygote, which is a single cell, becomes a fetus with several layers and with organs that already work, though still in a primitive, very basic way.
The key step comes in week 3 and is called gastrulation. The embryo organizes itself into three germ layers, the layers the organs later arise from: the endoderm, the mesoderm, and the ectoderm. Picture a three-layer cake that different organs grow from. The stage in which organs form from those layers is called organogenesis.
Each layer contributes its share. The endoderm gives rise to the organs of digestion and breathing, among others. The ectoderm gives rise to the skin and the nervous system. And the mesoderm gives rise to blood, bone, and muscle.
In brief
Embryonic development spans the first eight weeks: a single-celled zygote becomes a multilayered fetus with organs that function in a primitive way.
In week 3, gastrulation forms three germ layers (endoderm, mesoderm, and ectoderm) that give rise to the organs during organogenesis.
A three-layer cake that different organs grow from.
The endoderm gives rise to the digestive and respiratory organs, among others; the ectoderm, to the skin and nervous system; the mesoderm, to blood, bone, and muscle.
Sources (2)
- National Center for Biotechnology Information, StatPearls PublishingEmbryology, Week 1, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingEmbryology, Weeks 6-8, StatPearlsPublished
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