Cardio Embryology

How are the caudal vena cava and azygos v. formed? What is a portosystemic shunt?

Bilateral caudal cardinal vv. give rise to the caudal vena cava and azygos v. in a complicated process that involve proliferation of supra-cardinal and sub-cardinal veins. The adult caudal vena cava is patched together by anastomosis and degeneration of these cardinal veins plus vitelline veins. The patchwork process (illustrated below) produces venous variability. Embryonic vitelline veins gives rise to the adult portal v., which conveys blood from intestine to the liver. Placental blood is conveyed to the ductus venosus within the liver by one umbilical v. (the right umbilical v. atrophies). A postnatal portosystemic shunt anomaly allows portal blood from intestine to bypass liver detoxification. The intestinal blood reaches the heart and eventually impairs the brain. The shunt can result from a persistent ductus venosus or from development of anatomoses between the portal v. and either the caudal vena cava or the azygos vein.