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Superior and inferior mesenteric 'Veins

  1. Superior mesenteric vein is a large vein which drains blood from the small intestine, the appendix, the caecum, the ascending colon and the transverse colon. It is formed by the union of tributaries from ileocaecal region. It accompanies superior mesenteric artery and lies on right side of artery. It terminates, behind the neck of pancreas, by joining the splenic vein to form the portal vein. Its tributaries are: -
    1. Veins corresponding to the branches of SMA,
    2. Right gastroepiploic vein and
    3. Inferior pancreaticoduodenal vein.
  2. Inferior mesenteric vein drains blood from the rectum, the anal canal, the sigmoid colon and descending colon. It begins as superior rectal vein from the upper part of the internal rectal venous plexus. Superior rectal vein crosses left common iliac vessels and continues upwards as 'inferior mesenteric vein and drains into splenic vein. Its tributaries correspond to the branches of inferior mesenteric artery.

Portal vein

  1. The portal vein is about 8 cm long. It is formed by union of superior mesenteric vein and splenic veinbehind the neck of pancreasat the level of L2, vertebrae in front of inferior vena cava (IVC). The blood flow in portal vein is slow and there are no valves in portal vein. There is stream line flow, i.e. blood in superior mesenteric vein drains into right lobe of liver and blood in splenic vein (receiving inferior mesenteric vein) drains into left lobe.
  2. Before entering the liver through porta hepatis, portal vein divides into right and left bronchus. Right branch is shorter and wider, and after receiving cystic vein it enters the right lobe of liver. Left branch is longer and narrower, and just before entering the left lobe it receives: i) Paraumblical vein along with ligamentum teres (remnant of leftumbilical vein), and ii) Ligamentum venosum (remnant of ductus venosus).
  3. Portal vein passes behind 1st part of duodenum. Thus it can be divided into infraduodenal, retroduodenal and supraduodenal parts. Its relations are :
    1. Infraduodenal part
      1. Anterior: Neck of pancreas
      2. Posterior: IVC
    2. Retroduodenal part
      1. Anterior: 1st part of duodenum, bile duct, gastroduodenal artery.
      2. Posterior: IVC
    3. Supraduodenal part
      1. Anterior: Hepatic artery, bile duct
      2. Posterior:IVC, separated by epiploic foramen.
  1. Development of portal vein :
    1. Infra-duodenal part - part of left vitelline vein distal to the dorsal anastomosis.
    2. Retro-duodenal part - dorsal anastomosis between two vitelline veins.
    3. Supra-duodenal part - cranial part of right vitelline vein.
  2. The portal vein receives the following veins -
    1. Splenic vein,
    2. Superior mesenteric vein,
    3. Left gastric,
    4. Right gastric,
    5. Superior pancreatico-duodenal,
    6. Cystic and Paraumbilical veins.

Portal venous system refers to a venous system where vein begins from a capillary plexus and ends in a capillary plexus by dividing into branches like an artery. Venous blood circulates through an organ before reaching heart. Largest portal system is hepatic portal system formed by portal vein where its main tributary, the superior mesenteric vein, begins in one set of capillaries and portal vein ends in another set of capillaries in liver.


Portocaval anastomoses (portosystemic communications)

  • Tributaries of hepatic portal system anastomose with tributaries of systemic circulation, called portocaval anastomosis.

Sites of portocaval anastomoses


Portal vein

Systemic vein

Lower end of esophagus

Left gastric

Esophageal veins (tributaries of hemiazygous vein)



Above - Superior epigastric, lateral thoracic

Below - Superior epigastric, inferior epigastric

Sides - Posterior intercostal, lumbar

Lower end of rectum

Superior rectal

Middle and inferior rectal

Posterior abdominal wall


Left renal vein and other tributaries of IVC(veins of Retzius)

Bare area of liver

Portal radicles


Falciform ligament



Ligamentum venosum

Left branch of portal

IVC via ductus venosus

Posterior vaginal wall

Superior rectal

Vaginal venous plexus


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