Blood flows from the inferior vena cava, the superior vena cava and the coronary sinus into the right atrium. This blood can then move into the left ventricle and is pumped out directly to the aorta. The foramen ovale is a pulmonary shunt that allows blood to bypass the nonfunctional lungs. Blood that flows from the right atrium to the right ventricle is pumped out into the pulmonary trunk. The ductus arteriosus transfers most of the blood in the pulmonary trunk directly into the aorta, again bypassing the lungs.
Blood is carried to all parts of the fetus through systemic arteries that branch off the aorta.
The umbilical arteries extend to the placenta through the umbilical cord. The umbilical arteries subdivide into fetal capillaries in the placenta. The wastes in the fetal blood pass through the placenta and are then picked up by the mother's bloodstream. Oxygen and nutrients pass through the placenta from the mother's blood and are picked up by the fetal capillaries. The fetal capillaries join to form the umbilical vein, which carries the blood back to the fetus.