- membrane which encloses amniotic fluid, broken at birth. 
- protects foetus against mechanical shock, drying out and temperature fluctuations 
Placenta and umbilical cord
A placenta, connected by an umbilical cord, develops from the embryo.
The placenta anchors the embryo in the uterus.
It also allows:
- nutrients and oxygen to move from the mother to the embryo
- waste materials and CO2 to move from the embryo to the mother
There is no physical connection between the circulatory systems of the embryo and its mother, so their blood doesn’t mix.
These materials pass from one to the other by diffusion. 
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