The fetal circulation is different from the normal adult circulation. This is because these reasons, the fetus gets its blood supply from the mother's placenta and the lungs is still not capable for air exchange. That is why there are 3 types of openings in their circulation.
|simple drawing on normal fetal circulation|
The first one is the Ductus venosus, this opening is the conjunction between the child's liver and heart. The blood supply from the placenta will pass through this opening before it can enter the heart. This normally closes when the umbilical cord is cut and it will then result as ligamentum venosus.
The second opening is the foramen ovale. This can be found in between the two atrias. About 80% of blood supply from the right atrium will be shunted to the left atrium. Since the lungs of the fetus is still immature, it cannot hold too much blood supply. That is why some of the blood are shunted to the left atria. Foramen ovale closes due to the pressure from the left side of the heart coming from the lungs upon delivery and child's first breath.
The third opeing is the Ductus arteriosus. This is located as a conjunction between the pulmonary artery and aorta. The same reason applies to with the foramen ovale. Bare in mind that the lungs of the fetus is not used for air exchange while it is still inside the womb. The blood supply coming from the mother already carries nutrients and oxygen supply for the fetus. Blood supply that is distributed to the lungs are only for perfusion purposes. Ductus arteriousus normally closes within the first 6 weeks of life after child delivery.
|Normal fetal blood circulation diagram|