Final answer:
The foramen ovale is the opening in the interatrial septum that connects the right and left atrium in the fetal heart, allowing blood to bypass the lungs until after birth when it closes to become the fossa ovalis.option a.
Step-by-step explanation:
The opening in the interatrial septum of the fetal heart that connects the right and left atrium is known as the foramen ovale. This temporary opening allows blood to bypass the pulmonary circulation until the fetus begins breathing air after birth. Once the newborn starts to breathe, blood pressure changes cause this shunt to close, and the foramen ovale is replaced by the fossa ovalis, a depression in the septum marking the location of the closed shunt.
In contrast, the ductus arteriosus is a provisional vessel that connects the pulmonary trunk to the aorta. This structure along with the foramen ovale plays a critical role in fetal circulation by ensuring that oxygenated blood is efficiently distributed to the body, bypassing the non-functioning fetal lungs. After birth, the ductus arteriosus also closes and eventually forms the ligamentum arteriosum. The ductus venosus has a different role, diverting blood from the umbilical vein to the inferior vena cava, hence it is not related to the interatrial septum.