The umbilical veins are a pair of developmental vessels passing between the placenta and the sinus venosus of the heart. They carry oxygenated blood.
From the fifth week of development, part of the umbilical veins becomes incorporated into the region of the developing liver. The veins enlarge and anastomose within the developing parenchyma. They merge with the vitelline veins to form sinusoids.
Then, the right umbilical vein regresses along with the part of the left umbilical vein that is nearest to the heart. The distal part of the left umbilical vein is left to become the main channel through the liver. It forms an anastomosis with the right hepatocardiac channel, one of a pair of early vessels running between the liver and the heart. The route so formed provides a shunt to bypass the hepatic sinusoids. By three months' development, the right hepatocardiac channel has enlarged and is termed the ductus venosus.
The left umbilical vein regresses at birth into a fibrous cord; this forms the ligamentum teres hepatis. Also, the ductus venosus forms a fibrous cord, the ligamentum venosum.
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