Final answer:
The fossa ovalis is a small depression in the interatrial septum of the fetal heart. It is the remnant of the foramen ovale, which allows blood to flow from the right atrium to the left atrium during the fetal period. After birth, the foramen ovale closes and the fossa ovalis serves to isolate deoxygenated and oxygenated blood within the heart.
Step-by-step explanation:
The fossa ovalis is a small depression in the interatrial septum of the fetal heart. It is the remnant of the foramen ovale, an opening that allows blood to flow from the right atrium to the left atrium in the fetal period. This helps the developing fetus bypass the non-functioning fetal lungs.
After birth, as the newborn begins to breathe and blood pressure in the atria increases, the foramen ovale closes and the fossa ovalis remains as a permanent structure marking the former site of the opening. It isolates deoxygenated and oxygenated blood within the heart, directing it to the appropriate chambers for circulation.