| Vein: Umbilical vein | |
|---|---|
| Fetal circulation; the umbilical vein is the large, red vessel at the far left. | |
| Human embryo about fifteen days old. Brain and heart represented from right side. Digestive tube and yolk sac in median section. (Umbilical vein labeled at bottom right.) | |
| Latin | vena umbilicalis |
| Gray's | subject #135 519 |
| Artery | umbilical artery |
| Dorlands / Elsevier |
{{{DorlandsID}}} |
The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta to the growing fetus.
The blood pressure inside the umbilical vein is approximately 20 mmHg.[1]
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During embryologic development, there are two umbilical veins, left and right, that drain blood from the placenta to the heart.[2] The right umbilical vein regresses and under normal circumstances is completely obliterated during the second month of development.[2] The left umbilical vein persists and delivers blood from the placenta to the developing fetus.[2] The diameter of the intra-abdominal umbilical vein increases linearly, from 3 mm at 15 weeks of gestation to 8 mm at term.[3]
Within a week of birth, the infant's umbilical vein is completely obliterated and is replaced by a fibrous cord called the round ligament of the liver. It extends from the umbilicus to the transverse fissure, where it joins with the falciform ligament of the liver to separate the left and right lobes of the liver.
Closure of the umbilical vein usually occurs after the umbilical arteries have closed. This prolongs the communication between the placenta and fetal heart, allowing for a sort of autotransfusion of remaining blood from the placenta to the fetus.
Under extreme pressure, the round ligament may reopen to allow the passage of blood. Such recanalization is common in patients with cirrhosis and portal hypertension. Patients with cirrhosis experience rapid growth of scar tissue in and around the liver, often functionally obstructing nearby vessels. Vessel occlusion increases vascular resistance and therefore leads to hypertension. In portal hypertension, the vessels surrounding the liver are subjected to abnormally high blood pressure—so high, in fact, that the force of the blood pressing against the round ligament is sufficient to recanalize the structure.
A newborn baby has a patent umbilical vein for at least a week after birth. This umbilical vein may be catheterised for ready intravenous access. It may be used as a site for regular transfusion in cases of erythroblastosis or hemolytic disease.
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