About 6 days after fertilization, the egg has become a hollow ball of
cells (blastocyst), which implants on the inside wall of the uterus
(endometrium). After implantation, the blastocyst begins to develop into
the:
-
Embryo (the group of cells that will become the
fetus).
- Sac that contains the embryo (the
amniotic sac).
-
Placenta, which allows oxygen and other substances to
pass from the mother's blood to the embryo or fetus. The placenta also allows
wastes to pass from the fetus to the mother's blood and then to her kidneys for
elimination.
