the Vitelline and Umbilical Systems

• The blood vessels of the yolk sac give rise to the arteries and veins of the vitelline system
• anastomosis →connection formed between two vessels
• Body folding and growth of the embryo

  1. Reduces the size of the yolk sac

  2. Leads to fusion of the vitelline arteries and veins to the vascular plexus of the future gastrointestinal tract and the dorsal aorta

  3. Arteries and veins of the vitelline system lose their connection with the yolk sac altogether
• Remnants of the arterial vitelline system

  1. Anastomose with the ventral gastrointestinal branches of the dorsal aorta

  2. Supplying blood from the dorsal aorta to the gastrointestinal tract
• The arterial vitelline plexus


  Connected to the vitelline veins that empty in the horns of the sinus venosus
• Vessels of the arterial vitelline plexus in the gut

  1. Become surrounded by the growing liver

  2. Give rise to the liver sinusoids
• Liver sinusoids


  Form a dense network of anastomosing veins
• Disappearance of the left horn of the sinus venosus

  1. Due to remodeling of the inflow end of the heart

  2. The left vitelline vein also diminishes

  3. By the third month, the left vitelline vein has fully disappeared
• Blood that originally drained into the left vitelline vein

  Is now redirected through multiple anastomoses to the right vitelline vein
• Portion of the right vitelline vein in between the liver and the heart


  Becomes the terminal portion of the inferior vena cava
• Ductus venosus


  • A large vessel formed amidst the liver sinusoids
  • Forms a shunt between the (left) umbilical vein and the heart, draining directly into the inferior vena cava
• The ductus venosus is crucial for fetal life, permitting the incoming oxygenated placental blood to bypass the liver sinusoids to distribute it to the organs that need it most (e.g. the heart and brain)
• Vitelline veins caudal to the liver

  1. Regress during the second and third months

  2. Except for the portion directly caudal to the liver (and its associated anastomoses)
• Hepatic portal vein (vena portae)


  The main vein of the portal system which drains blood from the gastrointestinal tract to the liver sinusoids
• The portal vein contains parts of the original left and right vitelline veins
• The right umbilical vein completely regresses during the second month of the development.
• The left umbilical vein persists but loses its connection to the left sinus horn (which disappears during heart remodeling).
• The left umbilical vein transports all the oxygenated and nutrient-rich blood from the placenta directly to the ductus venosus, bypassing the liver.