Circulation through the liver

The fetus is supplied by oxygenated blood via two umbilical veins; the right umbilical vein regresses in late fetal life. The left vein persists to enter the abdomen via the umbilicus. It first travels to the liver within the falciform ligament. Before reaching the porta hepatis, it gives off several small branches which mainly enter the left lobe of the liver.

Within the porta hepatis, the left umbilical vein joins the left branch of the portal vein to form the ductus venosus. The ductus venosus joins the inferior vena cava having crossed the inferior surface of the liver within layers of lesser omentum. On route, it is joined by the left hepatic vein.

Hence, blood from the umbilical veins may take one of several routes through the liver:

• shunting directly through via the sinus venosus
• via the sinusoids and thence the hepatic veins and inferior vena cava in turn
• due to the greater pressure and flow within the umbilical vein relative to the portal vein, through branches of the latter to both lobes of the liver