Portal Vein (Hepatic Portal Vein)
The hepatic portal vein drains blood from the abdominal part of the Gastrointestinal tract from the lower third of the esophagus to halfway down the anal canal. It also drains blood from the spleen, pancreas, and gallbladder. The hepatic portal vein enters the liver and breaks up into sinusoids, from which blood passes into the hepatic veins that join the inferior vena cava. The portal vein is about 2 inch (5 cm) long and forms behind the neck of the pancreas by the union of the superior mesenteric and splenic veins. It ascends to the right, behind the first part of the duodenum, and enters the lesser omentum. It then runs upward in front of the opening into the lesser
sac to the porta hepatis, where it lies behind the bile duct and the hepatic artery. Finally, it divides into right and left terminal branches.
Tributaries of the Hepatic portal vein
Splenic vein:
Splenic vein leaves the hilum of the spleen and passes to the right in the splenorenal ligament. It unites with the superior mesenteric vein behind the neck of the pancreas to form the portal vein. It receives the short gastric, left gastro-omental, inferior mesenteric, and pancreatic veins.
Inferior mesenteric vein:
Inferior mesenteric vein ascends on the posterior abdominal wall and joins the splenic vein behind the body of the pancreas. It receives the superior rectal veins, the sigmoid veins, and the left colic vein.
Superior mesenteric vein:
Superior Mesenteric vein ascends in the root of the mesentery of the small intestine. It passes in front of the third part of the duodenum and joins the splenic vein behind the neck of the pancreas. It receives the jejunal, ileal, ileocolic, right colic, middle colic, inferior pancreaticoduodenal, and right gastro-omental veins.
Left gastric vein:
Left gastric vein drains the left portion of the lesser curvature of the stomach and the distal part of the esophagus. It opens directly into the portal vein.
Right gastric vein:
Right gastric vein drains the right portion of the lesser curvature of the stomach and drains directly into the portal vein.
Cystic veins:
Cystic veins either drain the gallbladder directly into the liver or join the portal vein.
Clinical Notes on Hepatic Portal Vein
Portal–Systemic Anastomoses
Under normal conditions, the portal venous blood traverses the liver anddrains into the inferior vena cava of the systemic venous circulation by way of the hepatic veins. This is the direct route. However, other, smaller communications exist between the portal and systemic systems, and they become important when the direct route becomes blocked.
These communications are as follows:
Gastroesophageal anastomosis.
At the lower third of the esophagus,the esophageal branches of the left gastric vein (portal tributary) anastomose with the esophageal veins draining the middle third of the esophagus into the azygos veins (systemic tributary).Anorectal anastomosis. Halfway down the anal canal, the superior rectal veins (portal tributary) draining the upper half of the anal canal anastomose with the middle and inferior rectal veins (systemic tributaries), which are tributaries of the internal iliac and internal pudendal veins, respectively.
Paraumbilical anastomosis.
The paraumbilical veins connect the left branch of the portal vein with the superficial veins of the anterior abdominal wall (systemic tributaries). The paraumbilical veins travel in the falciform ligament and accompany the ligamentum teres.
Retroperitoneal anastomoses.
The veins of retroperitoneal organs (duodenum, pancreas, ascending colon, and descending colon), plus the liver (portal tributaries), anastomose with the renal, lumbar, and phrenic veins (systemic tributaries).
Portal Hypertension
Portal hypertension is a common clinical condition that influences the portal–systemic anastomoses just described. Enlargement of the portal–systemic connections is frequently accompanied by congestive enlargement of the spleen. Portacaval shunts for the treatment of portal hypertension mayinvolve the anastomosis of the portal vein, because it lies within the lesser omentum, to the anterior wall of the inferior vena cava behind the entranceinto the lesser sac. The splenic vein may be anastomosed to the left renal vein after removing the spleen.
Blood Flow through Portal Vein and Malignant Disease
The portal vein conveys about 70% of the blood that enters the liver. The remaining 30% is oxygenated blood, which passes to the liver via the
hepatic artery. The wide angle of union of the splenic vein with the superior mesenteric vein to form the portal vein leads to streaming of the blood flow in the portal vein. The right lobe of the liver receives blood mainly from the intestine, whereas the left lobe plus the quadrate and caudate lobes receive blood from the stomach and the spleen. This distribution of blood may explain the distribution of secondary malignant deposits in the liver.
