EMBRYOLOGY OF THE UMBILICAL VEIN

2 - 4 WEEKS

• Two paired umbilical veins appear as paired structures, which join the vitelline and common cardinal veins and drain into the sinus venosus by 4-6 weeks.
• Three major vein pairs connect to the primitive fetal heart.
• Vitelline veins draining blood from yolk sac.
• Cardinal veins collecting blood from the embryo.
• Umbilical veins carry blood from placenta to embryo.
• The liver bud develops and the umbilical veins loose their connection to the sinus venosus and develop connections to the hepatic sinusoids (if this connection is not formed the right umbilical artery may persist).

4.5 WEEKS

• The right umbilical vein regresses and left umbilical vein persists and enters the hepatic sinusoids.
• The left umbilical vein later drains into the portal venous system. Later on a direct communication is established between the left portal vein and systemic circulation (ductus venosus).
• Still later on the umbilical vein shifts to the midline and occupies the free edge of the falciform ligament.