Ductus arteriosus functions in fetal circulation by connecting which structures?

• A. Opening between right and left atria
• B. Connection between right atrium and superior vena cava
• C. Vascular connection between the pulmonary artery and the aorta allowing bypass of lungs
• D. Valve between ventricles

Answer: (C)

In fetal life, the lungs aren’t used for oxygenating blood, so most blood must bypass them. The ductus arteriosus creates a direct vascular link between the pulmonary artery and the aorta. This shunt lets blood pumped into the pulmonary artery flow into the aorta and onward to the rest of the body, ensuring that oxygenated blood from the placenta reaches systemic circulation despite the nonfunctional lungs. After birth, increased oxygen and decreased prostaglandins cause it to constrict and eventually form the ligamentum arteriosum.