The umbilical vein is an important part of the fetal circulation. Unlike regular veins in adulthood, the fetal umbilical vein carries oxygenated blood from the placenta into the growing fetus. During fetal life, the umbilical vein arises within the placenta and passes through the umbilical cord, along with the paired umbilical arteries. After emerging from the umbilical cord, it passes superiorly within the layers of the falciform ligament to reach the porta hepatis.
Soon after birth, this vein usually obliterates and persists as the round ligament (ligamentum teres) of the liver. However, the lumen of the umbilical vein may reopen and by 5–6 mm in certain pathologic conditions.
|Drains from||Small venules of the placenta|
|Tributaries||Left branch of the portal vein|
|Drains to||Ductus venosus|
This article will discuss the anatomy and function of the umbilical vein.
Anatomy and course
During early fetal development, the umbilical vein exists as a paired vessel: a right and left umbilical vein. However, later in the development, the right umbilical vein atrophies completely leaving the left as the persisting vessel. For didactic purposes, we will only describe the left umbilical vein and refer to it as the umbilical vein.
The umbilical vein arises from multiple small veins within the placenta which carry oxygen and nutrient rich blood derived from the maternal blood circulation via the chorionic villi. From here, it enters the umbilical cord, along with the paired umbilical arteries. After emerging from the umbilical cord into the abdominal cavity of the fetus, it passes within the layers of the falciform ligament, running superiorly and to the right towards the porta hepatis. Near the porta hepatis, it gives off several large intrahepatic branches to the fetal liver and anastomoses with the left branch of the portal vein. Here, the umbilical vein ends by joining the ductus venosus, which drains into the inferior vena cava. Thus, the function of the umbilical vein is to carry oxygenated blood from the placenta to the ductus venosus, bypassing the liver and draining directly into the inferior vena cava.
Due to the changes in pressure after birth, the lumen of the umbilical vein obliterates. The fibrous remnant of the umbilical vein forms a cord that becomes the round ligament (ligamentum teres hepatis) in the adult. The supraumbilical falciform ligament encloses the remnant of the embryonic umbilical vein and the accompanying paraumbilical veins in its free edge.
Ductus venosus and ligamentum venosum
The ductus venosus receives the fetal umbilical vein, immediately after arising from the left branch of the portal vein. It continues for about 2–3 cm within the layers of the lesser omentum, running in a groove between the left and caudate lobes of the liver. It usually terminates in the inferior vena cava, however it may terminate in the left hepatic vein right before it joins the inferior vena cava.
It undergoes obliteration that begins in the second postnatal week and ends by the second or third month after birth, in which the ductus venosus becomes the ligamentum venosum. The function of ductus venosus is to shunt the blood from the umbilical vein into the inferior vena cava, thereby bypassing the liver.