The yolk sac gives rise to the first blood islandsthat will form the
vitelline vessels.
Passive immunity is transfered to the fetus by transport of
immunoglobulin G(IgG) from the maternal to the fetal circulation.
Excess amniotic fluid is swallowed by the fetus, absorbed by the fetal
GI tract, transferred to the fetal circulation, and finally crosses the placen-
tal membranes to the maternal circulation.
Hormones secreted by the placenta include chorionic gonadotropin
(HCG), estrogen, progesterone, and chorionic somatostatin (placental
lactogen).
High-Yield Facts 13