This is Fetal Circulation, Assignments of Anatomy

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Circulation during fetal development is necessarily different from that of an adult. During fetal development, the placenta is the site of the exchange of nutrients and oxygen from maternal blood to fetal blood

The umbilical vein brings oxygenated blood from the placenta to the fetus via the umbilical cord. The umbilical vein continues to the liver.

Near the liver, the umbilical vein gives off a branch, the ductus venosus, that by passes the liver to join a vein from the liver and merge with the inferior vena cava. This arrangement allows oxygen-rich blood to quickly enter the general circulation.

Two umbilical arteries carrying blood to the placenta are wrapped around the umbilical vein in the umbilical cord.

They are extensions of the hypogastric arteries (internal iliacs) that pass along each side of the urinary bladder.

During contraction, blood is pumped from the heart through both the pulmonary artery and the aorta. Since fetal lungs are non- functional, they receive less blood than adult lungs.

Much of the blood in the pulmonary artery passes into the aorta via the short ductus arteriosus and increases the volume of blood available to the body.

It subsequently becomes the ligamentum venosum of the liver. The umbilical vein becomes non-functional and is converted into the round ligament extending from the umbilicus to the liver.

The distal portions of the hypogastric arteries becomes fibrous cords, and the proximal portions remain functional and supply the urinary bladder.

The resulting increase in blood volume and pressure in the left atrium closes the flap on the foramen ovale. Subsequently, connective tissue seals this opening to permanently separate the atria.

Failure of the foramen ovale or ductus arteriosus to close after birth results in a circulatory defect that allows continued mixing of oxygenated and deoxygenated blood.