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What changes in circulation occur at birth when the lungs begin to exchange gases?

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Silhouette diagram of the human body highlighting the heart and major blood vessels, with labeled arteries in red and veins in blue to show the structure of the cardiovascular system. — Circulatory system Human circulatory system.

At birth, the transition to independent breathing triggers significant changes in the circulatory system to facilitate gas exchange in the lungs. As the lungs inflate with the first breaths and intrapulmonary fluid is evacuated, the pulmonary circulation—which was previously bypassed—opens to receive the full cardiac output.1

This shift involves the closure of specific fetal structures that once diverted blood away from the lungs:

Ductus arteriosus: This channel, which connects the pulmonary artery to the aorta in the fetus, normally closes after birth. Its closure separates the pulmonary and systemic circulations, ensuring that blood is properly routed through the lungs for oxygenation.23
Foramen ovale: This opening in the septum between the two atria of the heart, which allows blood to bypass the lungs during fetal life, also closes to ensure that blood flows through the pulmonary system.4

These adjustments allow the newborn to transition from receiving oxygen via the placenta to utilizing their own respiratory system for gas exchange.21