It is an essential vein that receives blood from the body and transports it to the liver for filtering and processing.
The term “hepatic” means or is related to the liver. Therefore, the hepatic portal vein is a blood vessel that sends blood rich in nutrients from the gastrointestinal tract and the spleen to the liver.
Veins of the liver
The liver is divided into eight numbered segments. Segments I to IV include the left anatomical liver and segments V to VIII, the right.
The right and left anatomical hemivicules are separated by an imaginary line that goes from the medial aspect of the gallbladder fossa to the inferior vena cava, parallel to the fissure of the round ligament.
This division is known as the Cantlie line or the central plane and marks the course of the middle hepatic vein.
The liver is divided into four sectors and eight segments based on the branching of the portal triad and the hepatic veins.
The portal triad structures (hepatic artery, portal vein, and bile duct) are separated in their extrahepatic path. However, they enter the hepatic hilum wrapped in a thickened layer of the Glisson capsule.
The central lobar fissure, also known as the principal plane or line of Cantlie, divides the right and left anatomical liver; there, we find the right suprahepatic vein, middle suprahepatic vein, left suprahepatic vein, central portal vein, right portal vein, left portal vein and vena cava.
The three central hepatic veins divide the liver into sectors, each of which is supplied by a portal pedicle:
- The right posterior sector (segments VI and VII).
- The right anterior sector (segments V and VIII).
- The left medial sector (segment IV).
The branches of the hepatic artery and the bile ducts follow those of the portal vein.
Portal vein function
The portal vein is a blood vessel that ensures the circulation of deoxygenated blood from the digestive organs and the spleen to the liver.
It gathers digestion products that contain carbohydrates and proteins from the intestines and transports them to the liver, releasing carbohydrates from the diet, which are used to fuel liver activity.
In addition to this critical function, the whole system of the portal acts as a reservoir of blood for the needs of the general circulation.
It has been calculated that the portal system can contain approximately one third of the total amount of blood in the body.
The portal vein transmits approximately 70 percent of the blood to the liver.
The remaining 30 percent is oxygenated blood, passing to the liver through the hepatic artery.
The amount of blood can be increased or decreased by physiological variations in the width of the arteries that enter the system and the terminal portions of the hepatic veins, through which it abandons it.
The portal vein is not a true vein, which means it does not drain into the heart.
Instead, it brings nutrient-rich blood to the liver from the gastrointestinal tract and spleen.
Once there, the liver can process the nutrients of the blood and filter the toxic substances it contains before the blood returns to the general circulation.
The condition can cause the growth of new blood vessels that bypass the liver, which can cause the circulation of unfiltered blood throughout the body.
Portal hypertension is one of the possible severe complications of liver cirrhosis, a condition in which normal liver tissue is replaced with scar tissue.
The increase in blood pressure in the hepatic portal vein leads to a certain number of clinical signs; this causes remarkably the enlargement of the spleen, called splenomegaly, accumulation of fluid in the abdomen, called ascites, and the development of a superficial venous circulation abnormally visible in the abdomen.
Occurrences of esophageal varices, where the veins of this organ are dilated, can lead to severe digestive hemorrhages.
Portal vein anatomy
This is a thick vein formed by the fusion of the mesenteric and superior splenic veins.
The portal vein is short, about 8 centimeters long in adults, and is found in the upper right quadrant of the abdomen.
The portal vein is peculiar between the veins because it begins like other veins because of the union of tributaries but ends as an artery when it divides into branches.
The spleen can be considered a specialized portion of the portal reservoir.
The valves are absent from the portal vein and its large tributaries but are present in some of its smaller tributaries, especially in the gastric veins.
While there may be some variation between individuals, the hepatic portal vein is usually formed by the convergence of the superior mesenteric and splenic veins, known as the splenic mesenteric confluence.
In some individuals, the hepatic portal vein also directly attaches to the inferior mesenteric vein. The cystic and gastric veins are even less common but also possible anastomoses.
The portal vein forms behind the neck of the pancreas by joining the veins. Run up to the right, behind the first part of the duodenum, and enter the lesser omentum.
Then it ascends in front of the opening in the lower sac towards the portal vein, where it is divided into right and left terminal branches.
Portal vein relations
The bile duct and the gastroduodenal artery lie between the portal vein and the first part of the duodenum, and there it faces the vena cava.
In the lesser omentum, it is separated from the vena cava by the opening in the lower sac. Its previous relationships are the bile duct again and the hepatic artery.
Its branches are located behind the branches of the hepatic artery and the hepatic ducts.
The portal vein receives direct tributaries such as the splenic and superior mesenteric veins. A pancreaticoduodenal vein is joined behind the duodenum, and right and left gastric veins join immediately before entering the lesser omentum.
Moreover finally, the cystic vein of the gallbladder that joins its right branch, the mesenteric vein of the small and large intestines, and the rectal vein of the rectum and anus.
Branches of the portal vein
The hepatic portal vein bifurcates into two distinct sections, with a branch penetrating each side of the liver, which originates behind the neck of the pancreas and is part of the hepatic portal system.
The right branch of the portal vein receives the cystic vein and then sinks into the right lobe of the liver.
The left branch, narrower and extended, runs towards the left end of the portal to sink into the left lobe.
Portal vein communications
At the left end of the portal, the left branch is joined by the venous ligament from behind and the round ligament from the front.
Some small veins, called paraumbilical veins, run around the long ligament and connect the left branch with the superficial veins around the navel when there is an obstruction to blood flow through the liver.
The paraumbilical veins enlarge and drain part of the blood in enlarged superficial veins that radiate from the navel, the so-called caput-medusae or palm tree sign.
Other communications are established with systemic veins by some of the peripheral veins of the splenic system, especially at the lower end of the esophagus by the left gastric vein and in the pelvis by the superior rectal vein.
The portal circulation begins as a capillary plexus in the organs that drain and empties its blood from the gastrointestinal tract.
The portal system begins in the capillaries and venules of the digestive system.
It collects venous blood from the lower part of the esophagus, the stomach, the duodenum, the jejunum, the ileum, the colon, and the spleen and administers it to the liver through the portal vein.
Consequently, portal blood contains the substances absorbed by the digestive tract. The average hepatic circulation is a system of high flow and low resistance.
The portal vein branches release 1000 to 1500 ml of blood per minute in the sinusoids of the hepatic lobes. The blood passes through the sinusoids and drains into the inferior vena cava.
The normal portal venous pressure is 5 to 10 mm Hg. When the pressure of the portal vein is more significant than 10 mm Hg, it may indicate portal hypertension.