The hepatic portal vein is a component of the hepatic portal system of human body. By definition, the hepatic portal vein drains deoxygenated, but nutrient rich blood from different organs to the liver. Thus it is not a true vein, which by definition should drain the deoxygenated blood into the heart.
The portal vein drains blood from the abdominal part of the gastrointestinal tract, which includes lower third of esophagus, stomach, all three parts of small intestine, all parts of the large intestine and upper half of the anal canal. It also drains blood from the accessory organs of digestive system including spleen, pancreas and gall bladder.
Origin and course of portal vein:
The portal vein is about 3 inches long and is formed behind the neck of the pancreas by the union of the superior mesenteric vein and splenic vein. After its origin, it ascends to the right behind the first part of duodenum to enter the lesser omentum. It then runs upward in front of the opening into the lesser omentum (epiploic foramen), and reaches the porta hepatis, where it divides into right and left terminal branches.
Portal vein in the liver:
Immediately before reaching the liver, the hepatic portal vein divides into right and left branches. Each branch enters the corresponding lobe of the liver, where they divide further into smaller venous branches leading into the portal venules. Each portal venule courses alongside a hepatic arteriole and the two vessels form the vascular components of the portal triad. The venules ultimately empty into the sinusoids of liver, which supply blood to the organ. From the sinusoids, the blood passes into the hepatic veins, which joint the inferior vena cava.
Tributaries of portal vein:
It leaves the hilum of the spleen and passes to the right in the splenicorenal ligament, where it lies below the splenic artery. Behind the neck of the pancreas, it unites with the superior mesenteric vein to form the portal vein. Thus the splenic vein is one of the major tributaries of the portal vein.
The splenic vein also receives a number of other veins that connect to the portal system through it. These veins include short gastric vein, left gastroepiploic vein, inferior mesenteric vein and pancreatic veins.
Inferior mesenteric vein:
The inferior mesenteric vein is not a direct tributary of the hepatic portal vein. Instead, it joints the splenic vein, which conveys all its blood to the portal vein. It ascends on the posterior abdominal wall and joins the splenic vein behind the body of the pancreas. It receives a number of tributaries including the superior rectal, sigmoid and left colic veins.
Superior mesenteric vein:
Along with the splenic vein, it is the major tributary of the hepatic portal vein. It ascends in the root of the mesentery of the small intestine on the right side of the superior mesenteric artery. It passes in front of the third part of duodenum and joins the splenic vein behind the neck of the pancreas. It receive a great number of other smaller veins including the jejunal, ileal, ileocolic, right colic, middle colic, inferior pancreaticoduodenal and right gastroepiploic veins.
Left gastric vein:
This vein drains the left portion of the lesser curvature of the stomach. It also drains the distal part of the esophagus. It opens directly into the portal vein and is thus a direct tributary of it.
Right gastric vein:
It is the counterpart of the left gastric vein and drains the right portion of the lesser curvature of the stomach. It also drains directly into the portal vein.
These are the veins of gall bladder and may drain into the portal vein or directly into the liver. Nevertheless, they form a component of the hepatic portal system