What structure serves as a protective barrier between the maternal and fetal blood supplies during pregnancy?

The placenta serves as a crucial protective barrier between the maternal and fetal blood supplies during pregnancy. It is a specialized organ that develops in the uterus and facilitates the exchange of nutrients, gases, and waste between the mother and the developing fetus while ensuring that their blood supplies do not mix. The placenta allows for the transfer of oxygen and nutrients from the mother's blood to the fetus, and it helps remove carbon dioxide and waste products from the fetal blood. Additionally, the placenta plays a vital role in producing hormones that support pregnancy and fetal development.

The amniotic sac, while important for cushioning and protecting the fetus, does not function as a barrier to blood supply. The umbilical cord primarily serves as the conduit through which blood, nutrients, and waste products travel between the placenta and the fetus, but it does not provide the same protective barrier as the placenta. Chorioamnion refers to the membranes that surround the fetus (chorion and amnion) and are involved in providing protection, but they do not manage the maternal-fetal blood supply relationship directly. Therefore, the placenta is the correct structure that fulfills the protective function described in the question.