Union of the superior mesenteric and splenic veins behind the neck of the pancreas
Mnemonic
“Superior mesenteric plus splenic, behind the neck of the pancreas, at L1”.
- Formed by the union of the superior mesenteric and splenic veins
- The inferior mesenteric vein usually joins the splenic vein
- Runs in the free edge of the lesser omentum as part of the portal triad
The portal triad arrangement is “duct to the right, artery to the left, vein behind”: common bile duct anterolateral on the right, hepatic artery anteromedial on the left, portal vein posterior. This is the structure occluded in the Pringle manoeuvre, entering through the epiploic foramen.
The portal vein has no valves, which is why portal hypertension transmits pressure freely back into the portosystemic anastomoses and produces varices.
Expansion
- Formed by the union of the superior mesenteric vein and the splenic vein, behind the neck of the pancreas, at about L1
- The inferior mesenteric vein usually joins the splenic vein
- Ascends in the free edge of the lesser omentum, posterior to the bile duct and hepatic artery
- Divides at the porta hepatis into right and left branches
It carries about 75 per cent of hepatic blood flow but only about half its oxygen, draining the whole gastrointestinal tract from the lower oesophagus to the upper rectum, plus the spleen, pancreas and gallbladder.
It has no valves, which is why raised pressure is transmitted backwards throughout the system and produces varices at the sites of portosystemic anastomosis. Other tributaries of note are the left and right gastric veins, the cystic vein and the paraumbilical veins.