ductus venosus

In the fetus, the ''ductus venosus'' (''"DV"''; Arantius' duct after Julius Caesar Aranzi) shunts a portion of umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver. Compared to the 50% shunting of umbilical blood through the ''ductus venosus'' found in animal experiments, the degree of shunting in the human fetus under physiological conditions is considerably less, 30% at 20 weeks, which decreases to 18% at 32 weeks, suggesting a higher priority of the fetal liver than previously realized. In conjunction with the other fetal shunts, the ''foramen ovale'' and ''ductus arteriosus'', it plays a critical role in preferentially shunting oxygenated blood to the fetal brain. It is a part of fetal circulation.

Anatomic course

The pathway of fetal umbilical venous flow is

umbilical vein $\rightarrow$ left portal vein $\rightarrow$ ''ductus venosus'' $\rightarrow$ ''inferior vena cava'' $\rightarrow$ eventually right atrium.

This anatomic course is important to recall when assessing the success of neonatal umbilical venous catheterization, as failure to cannulate through the ''ductus venosus'' results in malpositioned hepatic catheterization via the left or right portal veins. Complications of such positioning can include hepatic hematoma or abscess.

Postnatal closure

The ''ductus venosus'' is open at the time of birth, and that is the reason why a catheter inserted into the umbilical vein (umbilical vein catheterization / "UVC") can reach the inferior vena cava; absent a patent ''DV'', such a catheter would continue into the portal vein. The ''ductus venosus'' naturally closes during the first week of life in most full-term neonates; however, it may take much longer to close in pre-term neonates. Functional closure occurs within minutes of birth. Structural closure in term babies occurs within 3 to 7 days.

After the ''ductus venosus'' closes, its remnant is known as ''ligamentum venosum''.

If the ''ductus venosus'' fails to occlude after birth, it remains patent (open), and the individual is said to have a patent ''ductus venosus'' and thus an intrahepatic portosystemic shunt (PSS). This condition is hereditary in some dog breeds (e.g. Irish Wolfhound). The ''ductus venosus'' shows a delayed closure in preterm infants, with no significant correlation to the closure of the ''ductus arteriosus'' or the condition of the infant. Possibly, increased levels of dilating prostaglandins leads to a delayed occlusion of the vessel.

References

{{Veins

Embryology of cardiovascular system
Veins