Foramen secundum

The foramen secundum, or ostium secundum is a foramen in the septum primum, a precursor to the interatrial septum of the human heart. It is not the same as the foramen ovale, which is an opening in the septum secundum. The foramen secundum (from Latin, meaning 'second opening') is formed from small perforations that develop in the septum primum. The septum primum is a septum that grows down between the single primitive atrium of the developing heart to separate it into left and right atria. Once a baby is born, blood should flow through the lungs, which now function to provide oxygen to the blood. The foramen secundum and foramen ovale act as a shunt where blood bypasses the lungs and does not become oxygenated. To provide proper blood flow as a newborn, the foramen secundum and foramen ovale must close at birth. Since the lungs now require a significant amount of blood flow, the vessels going to and from the lungs undergo dilation. While the pulmonary artery and pulmonary veins are dilating, the umbilical artery and umbilical vein are severed at the cutting of the umbilical cord, or the funiculus umbilicalis. This combination results in a reversal of pressure differences between the atria, and the septum primum is permanently forced against the septum secundum. This holds true even during atrial diastole, when the pressure is significantly less than atrial systole. The septum primum is on the left side of the heart in the left atrium while the septum secundum is much thicker and is located on the right side, in the right atrium. During development, blood shunts from the floor of the right atrium through the foramen ovale in the septum secundum then up through the foramen secundum in the septum primum. The foramen secundum is positioned so that blood exits in the ceiling of the left atrium and then out through the left ventricle and the aorta. The position of the foramen secundum and the size of the septum primum are crucial to ensuring that blood not flow backwards from the left atrium to the right atrium. The septum primum, being much thinner, is easily pressed against the septum secundum if blood attempts to flow in the reverse direction, effectively sealing off both the foramen secundum and the foramen ovale. An ostium secundum that persists at large size can be a source of atrial septal defects. Foramen secundum atrial septal defects are the most common atrial septal defects. This defect can arise as a result of defects of the septum primum and the septum secundum. For the septum primum, the problem can arise as a result of excess resorption of the septum during the process of apoptosis in order to form the foramen secundum. For the septum secundum, its inadequate growth can cause atrial septal defect since it is supposed to grow and eventually overlap the foramen secundum so as to form the oval foramen. Newborns with small foramen secundum atrial septal defects have been shown to spontaneously correct by the third or fourth year of life. Therefore, medical supervision is generally accepted as a preventive measure for those diagnosed in infancy, rather than surgical intervention or use of other medical devices. If surgery is required, it is performed using minimally invasive techniques via robotic surgery that often requires only a few days of hospital stay. Surgical intervention should result in full closure of the foramen secundum, and mortality rates are similar to those for general anesthesia. The repair can be made by suturing the atrial septum or, if the foramen secundum is large in size, a patch can be made from the patient's pericardium to fully separate each atrium. The synthetic material Dacron may also be used to create a repair patch.