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In the developing fetus, the ductus arteriosus (DA) is a shunt connecting the pulmonary artery to the aortic arch that allows much of the blood from the right ventricle to bypass the fetus' fluid-filled lungs. During fetal development, this shunt protects the lungs from being overworked and allows the right ventricle to strengthen.
Closure at birth
When the newborn takes its first breath, pulmonary vascular resistance falls due to physical opening of the pulmonary capillaries and attenuation of intrauterine hypoxic pulmonary vasoconstriction. Decreased pulmonary vascular resistance increases pulmonary blood flow while pulmonary vascular pressure falls below aortic pressure. At the same time, the lungs release bradykinin and falling prostaglandin levels cause constriction of the smooth muscle in wall of the DA, reducing flow. Additionally, because of reduced pulmonary resistance, more blood flows from the pulmonary arteries to the lungs and thus the lungs deliver more oxygenated blood to the left heart. This further increases aortic pressure so that flow in DA may transiently reverse.
In normal newborns, the DA is closed within 15 hours after birth, and is completely sealed after three weeks. A nonfunctional vestige of the DA, called the ligamentum arteriosum, remains near the adult heart.
Patent ductus arteriosus
Failure of a child's DA to close after birth results in a condition called patent ductus arteriosus. If left uncorrected, patency leads to pulmonary hypertension and possibly congestive heart failure and cardiac arrhythmias.
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