Final answer:
In prenatal development, oxygenated blood enters the fetus via the umbilical vein from the placenta. The fetal circulatory system includes shunts such as the ductus venosus, umbilical vein, ductus arteriosus, and foramen ovale to facilitate efficient blood flow.
Step-by-step explanation:
The fetus receives oxygenated blood from the placenta via the umbilical vein. This blood flow is part of the prenatal circulation, an essential component of fetal development. Within the prenatal circulatory system, there are three major shunts, one of which is the umbilical vein that connects to the ductus venosus, allowing oxygen-rich blood to bypass the liver and flow directly to the fetus's heart. After the blood nourishes the fetus, it returns to the placenta through the umbilical arteries, carrying carbon dioxide and waste products away from the fetus to be expelled by the mother's body.
Additionally, the fetal circulatory system uses adaptive pathways like the ductus arteriosus and the foramen ovale to redirect blood from the pulmonary circulation to the systemic circulation due to nonfunctioning fetal lungs.