What does the ductus arteriosus do in fetal circulation?

The ductus arteriosus plays a crucial role in fetal circulation by providing a pathway that bypasses the fetal lungs. In the womb, the fetus does not utilize its lungs for breathing; instead, it receives oxygen directly from the mother through the placenta. The ductus arteriosus is a vessel that connects the pulmonary artery (which would normally carry blood to the lungs) directly to the aorta. This connection allows most of the blood to flow from the right ventricle into the aorta rather than the lungs, which are filled with fluid and not functional for gas exchange at this stage. After birth, when the lungs inflate and begin to function, the ductus arteriosus typically closes, thus normalizing the flow of blood through the circulatory system.

In fetal circulation, the other options do not accurately describe the function of the ductus arteriosus. Blood supply to the brain and delivery of deoxygenated blood to the placenta involve different pathways in fetal circulation. Additionally, while some blood may supply oxygen to the heart, the primary role of the ductus arteriosus is specifically to bypass the lungs.