Assertion: placenta | /r/CapableOf | take over nourishing the embryo
Facets:
value: at week
type: TEMPORAL
Source sentences:
text: When the placenta takes over nourishing the embryo at approximately week 4, the yolk sac has been greatly reduced in size and its main function is to serve as the source of blood cells and germ cells (cells that will give rise to gametes).