Definition – What is the Foramen ovale?
The heart consists of two atria and two chambers, which are normally separated from each other. However, the Foramen ovale represents an opening, which causes blood to pass from the right atrium to the left atrium in the fetus. Normally, blood would pass from the right atrium into the right chamber and via the pulmonary circulation into the left atrium.
In fetal circulation, most of the pulmonary circulation is drained from the blood stream, which is functionally enabled by the short circuit through the foramen ovale. The reason for the detour of the blood is that the lungs are not yet able to take over respiratory function in the fetus and therefore only little blood circulation is required initially. The foramen ovale closes due to the birth process and the functional absorption of the lung.
Anatomy of the heart
The heart consists of a right and a left atrium as well as a right and a left ventricle. Between the two atria is the atrial septum, which divides the heart into a right and a left half. The atrial septum is thinner compared to the ventricular septum and has a thinner muscle layer.
Blood enters the right atrium via two major body veins, the inferior vena cava and superior vena cava. From there, the blood is directed to the right ventricle and further into the pulmonary circulation. Via the pulmonary veins, the oxygen-enriched blood from the pulmonary circulation returns to the left atrium.
Here it is passed on via the left ventricle into the aorta and thus into the large circulation of the body. In the fetal circulation, there is an opening between the right and left atrium called the oval foramen. This opening is absolutely normal, since the lungs are not yet ventilated in the fetal circulation.
After birth, when the pulmonary circulation is opened, changes in pressure within the heart cause the blood circulation to change, now via the right ventricle and the pulmonary circulation into the left atrium. The Foramen ovale is no longer needed, so that it usually closes quickly. If the Foramen ovale does not close or closes incompletely, pathological clinical pictures may occur.
