The first three days of embryonic development occur in the fallopian tube as the embryo moves from the ovary to the uterus. Cell division continues and forms a hollow ball of cells (the blastocyst).
Six days after fertilization, the embryo begins implantation into the lining of the uterus. During the next few weeks the placenta begins producing the hormones that will cause the mother to supply the embryo with nutrients and oxygen.
In addition, the placenta protects the fetus from immune attack by the mother, removes waste products from the fetus, induces the mother to bring more blood to the placenta, and near the time of delivery, produces hormones that mature the fetal organs in preparation for life outside of the uterus.
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