Fetal Circulation The fetus- Has blood that is oxygenated in the placenta rather than in the lungs.
- Has three shunts that partially bypass the lungs and liver.
Foramen ovale- Is an opening in the septum secundum.
- Usually closes functionally at birth, but with anatomic closure occurring later.
- Shunts blood from the right atrium to the left atrium, partially bypassing the lungs (pulmonary circulation).
Ductus arteriosus- Is derived from the sixth aortic arch and connects the bifurcation of the pulmonary trunk.
- Closes functionally soon after birth, with anatomic closure requiring several weeks.
- Becomes the ligamentum arteriosum, which connects the left pulmonary artery (at its origin from the pulmonary trunk) to the concavity of the arch of the aorta.
- Shunts blood from the pulmonary trunk to the aorta, partially bypassing the lungs (pulmonary circulation
Ductus venosus- Shunts oxygenated blood from the umbilical vein (returning from the placenta) to the IVC, partially bypassing the liver (portal circulation).
- Joins the left branch of the portal vein to the IVC and is obliterated to become the ligamentum venosum after birth.
Umbilical arteries- Carry blood to the placenta for reoxygenation before birth.
- Become medial umbilical ligaments after birth, after their distal parts have atrophied.
Umbilical veins- Carry highly oxygenated blood from the placenta to the fetus.
- Consists of the right vein, which is obliterated during the embryonic period, and the left vein, which is obliterated to form the ligamentum teres hepatis after birth.
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