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Fetal Circulation and Changes at Birth

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

Adult Remnant

Foramen ovale

Fossa ovalis of the heart

Ductus arteriosus

Ligamentum arteriosum

Left umbilical vein

 

Extra-hepatic portion

Ligamentum teres hepatis

Intra-hepatic portion (ductus venosus)

Ligamentum venosum

Left and right umbilical arteries

 

Proximal portions

Umbilical branches of internal iliac arteries

Distal portions

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.

 

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Last modified: Thursday, 06-Jan-2000 13:11:44 EST