During fetal circulation, which structure allows blood to bypass the liver?

In fetal circulation, the ductus venosus plays a crucial role by allowing a significant portion of the blood from the umbilical vein to bypass the liver. This structure connects the umbilical vein directly to the inferior vena cava, directing oxygen-rich blood into the systemic circulation and ensuring that nutrients and oxygen from the placenta reach the developing fetus efficiently.

By bypassing the liver, which is not fully functional in the fetus, the ductus venosus helps prioritize the delivery of oxygenated blood to vital organs, such as the heart and brain, during critical stages of fetal development. Additionally, once the baby is born and the umbilical cord is cut, this structure typically closes and becomes a ligament known as the ligamentum venosum, marking the transition from fetal to postnatal circulation.

The other structures listed serve different functions in fetal circulation. For instance, the ductus arteriosus connects the pulmonary artery to the aorta and allows blood to bypass the lungs, while the foramen ovale permits blood flow between the right and left atria, also reducing pulmonary circulation. The pulmonary trunk is a major vessel carrying blood to the lungs, rather than a structure that bypasses any organs. Understanding these distinctions helps clarify