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How does blood circulation change in a newborn after breathing begins?
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prenatal development
An ultrasound image of a human fetus.
In the fetus, the circulatory system is designed to bypass the nonfunctional lungs, relying instead on the placenta for oxygenation. This is facilitated by specific structures, including the ductus arteriosus, which connects the pulmonary artery to the aorta, and the foramen ovale, an opening between the heart's atria.1234
When a newborn begins to breathe, the lungs inflate and intrapulmonary fluid is evacuated. This transition triggers significant physiological changes:15
- Pulmonary Circulation: The lungs open to accept the full cardiac output, allowing blood to flow through the pulmonary system for oxygenation rather than being bypassed.5
- Closure of Shunts: The ductus arteriosus normally closes shortly after birth, effectively separating the pulmonary and systemic circulations.12
- Systemic Integration: With the lungs functional and the fetal shunts closed, the newborn's heart and blood vessels reorganize to support independent respiration and circulation.5
Failure of these structures to close properly can lead to conditions such as patent ductus arteriosus, which may require medical or surgical intervention to prevent circulatory complications.12