The portal vein collects blood from all unpaired organs of the abdominal cavity, with the exception of the liver: from the entire gastrointestinal tract, where nutrients are absorbed through the portal vein to the liver for neutralization and deposition of glycogen; from the pancreas, where insulin comes from, which regulates sugar metabolism; from the spleen, from which the decay products of blood elements, used in the liver to produce bile, come from. The constructive connection of the portal vein with the gastrointestinal tract and its large glands (liver and pancreas) is due, in addition to the functional connection, and their common development (genetic connection).
V. portae, portal vein, is a thick venous trunk, located in lig. hepatoduodenale along with the hepatic artery and ductus choledochus. Composed v. portae behind the head of the pancreas from the splenic vein and two mesenteric – upper and lower. Heading to the gate of the liver in the above-mentioned bundle of peritoneum, it receives vv along the way. gastricae sinistra et dextra and v. The prepylorica and in the gates of the liver are divided into two branches that go into the liver parenchyma. In the parenchyma of the liver, these branches break up into many small branches that intertwine hepatic lobules (vv. Interlobulares); numerous capillaries penetrate into the lobules and are ultimately formed in vv. centrales (see “Liver”), which are collected in the hepatic veins flowing into the inferior vena cava. Thus, the portal vein system, unlike other veins, is inserted between two networks of capillaries: the first network of capillaries gives rise to venous trunks, of which the portal vein is folded, and the second is located in the liver substance, where the portal vein is divided into its final ramifications.
V. lienalis, the splenic vein, carries blood from the spleen, stomach (through v. Gastroepiploica sinistra and vv. Gastricae breves) and from the pancreas, along its upper edge behind and below the artery of the same name to v. portae.
Vv. mesentericae superior et inferior, superior and inferior mesenteric veins, correspond to the arteries of the same name. V. mesenterica superior on its way takes in the venous branches from the small intestine (vv. Intestinales), cecum, ascending colon and transverse colon (v. Colica dextra and v. Colica media), and, passing behind the head of the pancreas, connects to the inferior mesenteric vein. V. mesenterica inferior begins from the venous plexus of the rectum, plexus venosus rectalis. Heading up from here, it enters the pathway from the sigmoid colon (vv. Sigmoideae), from the descending colon (v. Colica sinistra) and from the left half of the transverse colon. Behind the head of the pancreas, having connected previously with the splenic vein or independently, it merges with the superior mesenteric vein.