Formation
Almost right immediately after the infant is born, the foramen ovale and ductus arteriosus close. The major changes that are made by the body are done right at the first breath (in the case of heart and lung functions) and up to weeks after birth (such as the liver's enzyme synthesis). The foramen ovale becomes the fossa ovalis as the foramen closes. This enables respiration and circulation independent from the mother's.
With the child's first breath, the lung sends oxygenated blood to the left atrium. As a resulting pressure in the left atrium is higher than that of the right, and the increased pressure holds the interatrial flap (which covers the foramen ovale) shut, therefore closing the foramen ovale as well. In normal development, the close foramen ovale fuses with the interatrial wall. During the first breath, vasoconstriction causes the ductus arterious to close, and during adult years, tissue occludes what once was the ductus arterious, creating the ligamentum arteriosum.
Read more about this topic: Fossa Ovalis (heart)
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