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Fetal Circulation and Changes at Birth

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General
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.
Circulatory Changes at Birth
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
Fetal Structure
Foramen ovale
Ductus arteriosus
Left umbilical vein
Extra-hepatic portion
Intra-hepatic portion
(ductus venosus)
Left and right umbilical
arteries
Proximal portions
Distal portions
Adult Remnant
Fossa ovalis of the heart
Ligamentum arteriosum
Ligamentum teres hepatis
Ligamentum venosum
Umbilical branches of internal
iliac arteries
Medial umbilical ligaments
Clinical Correlations
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.
Copyright © 2015 Thomas R. Gest
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