In light blue, the mesenteric vein draining the bowel and the splenic vein draining the spleen join to form the main portal vein that enters the liver and gives the intrahepatic portal veins. This allows the blood coming from the bowel with products of digestion to be filtered through the liver before getting to the heart via the hepatic veins

In purple, the inferior vena cava drains the blood from the inferior part of the body and receives the two renal veins and the hepatic vein just before joining the heart in the right atrium.

After birth, there is no direct communication between the portal and systemic veins.