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extraembryonic membranes

Thursday 17 February 2022

Extraembryonic membranes

The yolk sac, amnion , chorion , and allantois are the four extraembryonic membranes that lie outside of the embryo and are involved in providing nutrients and protection to the developing embryo.

They form from the inner cell mass; the first to form is the yolk sac followed by the amnion which grows over the developing embryo.

The amnion remains an important extraembryonic membrane throughout prenatal development.

The third membrane is the allantois, and the fourth is the chorion which surrounds the embryo after about a month and eventually fuses with the amnion.