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282 SECTION III CARDIOvASCuLAR ``CARdIOvASCulAR—EMbRYOlOGY CARDIOvASCuLAR ``CARdIOvASCulAR—ANATOMY
Fetal circulation Blood in umbilical vein has a Po 2 of ≈ 30 mm Hg
and is ≈ 80% saturated with O 2 . Umbilical
S Ductus arteries have low O 2 saturation.
arteriosus
3 important shunts:
LA Blood entering fetus through the
Superior vena cava umbilical vein is conducted via the ductus
Pulmonary venosus into the IVC, bypassing hepatic
R Foramen ovale RA artery
circulation.
RV LV Most of the highly Oxygenated blood
Q Ductus reaching the heart via the IVC is directed
venosus
through the foramen Ovale into the left
Aorta atrium.
Deoxygenated blood from the SVC
Inferior vena cava passes through the RA RV main
pulmonary artery Ductus arteriosus
Descending aorta; shunt is due to high
Portal vein
fetal pulmonary artery resistance (due
partly to low O 2 tension).
At birth, infant takes a breath resistance
Umbilical vein in pulmonary vasculature left atrial
pressure vs right atrial pressure foramen
ovale closes (now called fossa ovalis); in O 2
Internal iliac artery (from respiration) and in prostaglandins
(from placental separation) closure of ductus
Umbilical High O 2 arteriosus.
To placenta arteries Moderate O 2 Indomethacin helps close the patent Ductus
From placenta Low O 2 arteriosus ligamentum arteriosum (remnant
of ductus arteriosus). Come In and close the
Very low O 2
Door.
Prostaglandins E 1 and E 2 kEEp PDA open.
Fetal-postnatal derivatives
FETAl STRuCTuRE POSTNATAl dERIvATIvE NOTES
Ductus arteriosus Ligamentum arteriosum Near the left recurrent laryngeal nerve
Ductus venosus Ligamentum venosum
Foramen ovale Fossa ovalis
Allantois urachus Median umbilical ligament Urachus is part of allantoic duct between
bladder and umbilicus
Umbilical arteries Medial umbilical ligaments
Umbilical vein Ligamentum teres hepatis (round ligament) Contained in falciform ligament
Notochord Nucleus pulposus
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