What structure connects the pulmonary artery to the aorta, bypassing the lungs in fetuses?

The ductus arteriosus is a crucial structure in fetal circulation that connects the pulmonary artery to the aorta, allowing blood to bypass the non-functioning lungs. In a developing fetus, the lungs are filled with fluid and do not serve the purpose of oxygenating blood, as the mother’s placenta provides oxygenated blood.

The ductus arteriosus enables oxygen-rich blood from the placenta, which typically enters through the umbilical vein, to flow into the aorta and be distributed to the rest of the body while redirecting some blood from the right ventricle away from the pulmonary artery. After birth, when the lungs expand and begin functioning, the ductus arteriosus normally closes and forms a fibrous band, becoming the ligamentum arteriosum. This change is essential to establish normal postnatal circulation patterns, where the right ventricle pumps blood into the lungs for oxygenation.

The other structures mentioned serve different purposes in fetal circulation. The ductus venosus facilitates blood flow from the umbilical vein directly to the inferior vena cava, bypassing the liver. The foramen ovale is an opening between the right and left atria, allowing blood to flow from the right atrium to the left