After fetal circulation shifts, which structure carries oxygen-rich blood from the lungs to the heart?

After fetal circulation shifts, the pulmonary vein plays a crucial role in carrying oxygen-rich blood from the lungs to the heart. In a fetus, most of the oxygen-rich blood comes from the placenta through the umbilical vein. However, after birth, the lungs become the primary source of oxygen as the newborn begins to breathe air.

Once the lungs are functional, oxygenated blood that has returned to the heart from the lungs is channeled through the pulmonary veins. These vessels transport oxygen-rich blood from each lung directly into the left atrium of the heart, thereby allowing this oxygenated blood to be pumped out to the rest of the body via the aorta. This shift is vital for the newborn’s transition to life outside the womb.

The other structures mentioned, like the aorta, umbilical vein, and inferior vena cava, serve different roles in the circulatory system and do not transport oxygen-rich blood from the lungs to the heart in the context of postnatal circulation. The aorta distributes oxygenated blood to the body, while the umbilical vein is only relevant prior to birth, carrying oxygen-rich blood from the placenta. The inferior vena cava brings deoxygenated blood from the lower body to the heart, rather