The fossa ovalis is a remnant of which fetal structure?

The fossa ovalis is a remnant of which fetal structure?

• A. Ductus arteriosus
• B. Foramen ovale
• C. Umbilical vein
• D. Ductus venosus

Answer: (B)

The main idea tested is how fetal shunts become permanent structures after birth. In the fetus, the foramen ovale provides a direct passage from the right atrium to the left atrium, allowing blood to bypass the nonfunctional lungs. After birth, the pressure in the left atrium rises and the septa fuse to close this opening, leaving a shallow depression called the fossa ovalis—the remnant of the foramen ovale. The other options are different fetal structures with distinct postnatal remnants: the ductus arteriosus connects the pulmonary artery to the aorta and becomes the ligamentum arteriosum; the umbilical vein carries blood from the placenta and becomes the ligamentum teres hepatis; the ductus venosus shunts blood past the liver and becomes the ligamentum venosum.

The main idea tested is how fetal shunts become permanent structures after birth. In the fetus, the foramen ovale provides a direct passage from the right atrium to the left atrium, allowing blood to bypass the nonfunctional lungs. After birth, the pressure in the left atrium rises and the septa fuse to close this opening, leaving a shallow depression called the fossa ovalis—the remnant of the foramen ovale. The other options are different fetal structures with distinct postnatal remnants: the ductus arteriosus connects the pulmonary artery to the aorta and becomes the ligamentum arteriosum; the umbilical vein carries blood from the placenta and becomes the ligamentum teres hepatis; the ductus venosus shunts blood past the liver and becomes the ligamentum venosum.