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How do the foramen ovale and ductus arteriosus function before birth?
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Circulatory system
Human circulatory system.
In the fetus, the foramen ovale and ductus arteriosus function as critical shunts that allow blood to bypass the non-functional fetal lungs, which do not yet participate in gas exchange.12
- Foramen Ovale: This opening in the septum between the two atria allows oxygenated blood arriving from the placenta via the inferior vena cava to pass directly from the right atrium into the left atrium. From there, the blood enters the left ventricle and is pumped into the aorta to supply the head and upper extremities.12
- Ductus Arteriosus: This channel connects the pulmonary artery to the aorta. It diverts the majority of deoxygenated blood that enters the right ventricle away from the lungs and into the dorsal aorta. This blood then travels back to the placenta for re-oxygenation.312
These structures close shortly after birth when the lungs inflate, establishing the independent pulmonary and systemic circulatory systems.32