How does the ductus arteriosus typically close after birth?

The closure of the ductus arteriosus after birth primarily occurs due to elevated oxygen tension and decreasing vascular resistance. This anatomical structure, which connects the pulmonary artery to the aorta during fetal development, serves to bypass the non-functioning lungs. After birth, when the newborn takes its first breaths, the lungs expand and oxygen levels in the blood markedly increase.

As the oxygen tension rises in the blood, it leads to changes in the smooth muscle tone of the ductus arteriosus. The increased oxygen levels induce vasoconstriction of the ductal smooth muscle, promoting its closure. Additionally, the decrease in pulmonary vascular resistance allows blood to flow through the lungs, changing the dynamics of blood circulation. This combination of high oxygen tension and reduced resistance effectively causes the ductus arteriosus to close and eventually form a fibrous ligament known as the ligamentum arteriosum.

Other mechanisms, such as mechanical pressure from breathing, can contribute to the functional closure of the ductus during the initial moments after birth, but the critical factors that facilitate permanent closure are the changes in oxygen levels and vascular resistance.