The fine hair on a newborn infant is known as lanugo. It helps to anchor vernix caseosa (“cheese-like varnish”), a waxy substance that protects the fetus from maceration by the amniotic fluid.
At birth, placental blood flow ceases and lung respiration begins. The sudden drop in right atrial pressure pushes the septum primum against the septum secundum, closing the foramen ovale. The ductus arteriosus begins to close almost immediately, and may be kept open by the administration of prostaglandins. Other embryonic circulatory vessels are slowly obliterated and remain in the adult only as fibrous remnants.
Table 17 - Adult Remnants of Fetal Circulatory Structures
Patent Foramen Ovale
Failure of the foramen ovale to close at birth, e.g., due to faulty development of the septum primum and/or septum secundum. This condition is usually physiologically insignificant.
Patent Ductus Arteriosus
Failure of the ductus arteriosus to close after birth.
Patients with some heart anomalies can survive only if they have a patent
ductus arteriosus. Administration of prostaglandins can delay the closure of the
ductus arteriosus. Conversely,
drugs that inhibit prostaglandin synthesis (e.g. with indomethacin) can
sometimes be used to close the ductus arteriosus without surgery.