Final answer:
The interventricular septum separates the heart's lower chambers, the ventricles, and is quite thick to handle high pressures. The interatrial septum separates the upper chambers, the atria, and features the fossa ovalis, a remnant of a fetal circulation structure.
Step-by-step explanation:
The interventricular septum and interatrial septum serve as important internal structures of the heart, each separating different chambers within this vital organ. The interventricular septum separates the two lower chambers of the heart, which are the left and right ventricles. This septum is significantly thicker than the interatrial septum as it must withstand the greater pressure generated by the ventricles during contraction.
Conversely, the interatrial septum divides the two upper chambers, or atria, of the heart. In adults, the interatrial septum features a depression known as the fossa ovalis, a remnant of the fetal heart's foramen ovale, which allowed blood to bypass the pulmonary circuit before birth. After birth, the opening is closed, and the typical cardiac circulation pattern is established.