Third Week of Development
Gastrulation and Germ Layer Formation
During gastrulation, the embryo develops three germ layers (endoderm, mesoderm, and ectoderm), which differentiate into distinct tissues.
Following gastrulation, the neurulation process develops the neural tube in the ectoderm, above the notochord of the mesoderm.
Somites develop from the paraxial mesoderm and participate in the facilitation of multiple developmental processes.
Cardiovascular System Development
The circulatory system develops initially via vasculogenesis, with the arterial and venous systems developing from distinct embryonic areas.
Chorionic Villi and Placenta Development
In the placenta, chorionic villi develop to maximize surface area contact with maternal blood for nutrient and gas exchange.