The Anatomy of the Portal Vein

The portal vein is the main blood vessel that delivers blood to the liver from the gastrointestinal (GI) tract, including the stomach, intestines, spleen, and pancreas. This blood contains all the products absorbed by the GI tract. Some are filtered by the liver and discarded as waste, and others are broken down for use in the body.

Congenital portal vein defects may require surgical correction. The portal vein is also vulnerable to diseases like cirrhosis, which can change the structure of the vessel and reduce the flow of blood into the liver. This leads to a serious medical complication known as portal hypertension.

This article describes the anatomy and function of the portal vein. It also reviews common medical problems associated with the portal vein and ways to treat those conditions.

Portal Vein Location and Anatomy

The portal vein is formed by the merging of the splenic vein, which brings blood from the spleen, and the superior mesenteric vein, which brings blood from the intestines. Smaller veins from the stomach and pancreas also contribute to portal vein blood flow.

The splenic vein and superior mesenteric vein join behind the neck of the pancreas to form the main portal vein. This then travels within the hepatoduodenal ligament toward the portion of the liver called the liver hilum.

There, the vein splits into the right and left portal vein branches. These enter the main section of the liver. The right and left portal veins then branch further to supply the different lobes of the liver.

Collectively, these veins are called the hepatic portal venous system. If you have chronic liver disease, this system is at risk for serious complications.

Anatomical Variations

Up to 29% of people have variations in the branching pattern of the portal vein. These variants don’t usually cause symptoms or disease but become important if liver surgery is being planned.

Rarely, children may be born with an absent or underdeveloped portal vein. This condition, known as congenital agenesis of the portal vein, may be associated with abnormalities of the liver or cardiovascular system. Symptoms may be caused by blood flowing directly from the intestines and spleen into the systemic veins (portosystemic shunts).

For someone born with congenital agenesis of the portal vein, their prognosis depends on the nature of the liver and cardiac disease. Location of the shunts also affects your overall health. The condition can sometimes be managed with medications or minimally invasive surgical procedures. In severe cases, a liver transplant may be necessary.

Function

Like any organ, the liver requires a constant flow of blood to maintain life. The liver has a dual blood supply derived from the portal vein and the hepatic artery. Most of the blood flow comes from the portal vein, which is responsible for providing much of the liver’s oxygen and nutrients.

The liver helps metabolize carbohydrates, proteins, and fats that you eat. It also detoxifies many harmful substances (drugs and toxins) which are absorbed by the gastrointestinal (GI) tract. Nutrients and other substances that are absorbed in the intestines travel via the portal vein to the liver, where they can be processed before being released to the rest of the body.

Related Conditions

A number of conditions can affect the hepatic portal venous system while problems that originate with the portal vein can lead to other health complications.

Cirrhosis and Liver Disease

Chronic liver disease including cirrhosis can impede portal vein function and your general health. One issue is the build-up of fluid called “ascites” in the abdominal cavity.

Cirrhosis causes pressure to be exerted on the portal venous; it also causes sodium retention. These factors lead to a situation in which fluid seeps out, causing ascites to build up in the abdominal cavity. These fluid ascites can cause a variety of issues including:

• Increased abdominal girth
• Pressure on the diaphragm, abdominal wall, and stomach
• Shortness of breath
• Abdominal pain
• Feeling full after even small meals or snacks

Heading Encephalopathy

Hepatic encephalopathy is a complication of cirrhosis characterized by problems with cognitive and motor function. In severe cases, hepatic encephalitis can affect your consciousness.

This condition increases pressure on the vein and forces blood away from the liver. Toxic substances—normally processed by the liver—are allowed to circulate throughout the body. This affects brain function.

Portal Hypertension

Liver cirrhosis and other chronic liver diseases may disrupt blood flow in the portal vein. In addition, cirrhosis actually distorts the liver's structure, causing blood congestion in the portal vein and, ultimately, raising your blood pressure. This state is called portal hypertension.

Portal hypertension is responsible for the major complications of cirrhosis such as:

• Ascites
• Hepatic encephalopathy
• GI bleeding

With portal hypertension, blood in the portal venous system attempts to bypass the liver as portal pressure increases. Abnormal connections (portosystemic collaterals) form between the portal venous system and the systemic veins. Large portosystemic collaterals around the stomach and esophagus (called varices) can cause gastrointestinal bleeding that may be life-threatening.

Portal Vein Thrombosis

Portal hypertension can also be caused by clots forming in the portal vein. This is called portal vein thrombosis.

In adults, thrombosis of the portal vein may result from genetic conditions that increase the likelihood of clot formation.

Treatment of Portal Vein Disorders

Treating portal vein disorders starts with treating the underlying issue.

In cases of cirrhosis, the source of the cirrhosis must be eliminated. Thus, you may need to abstain completely from alcohol or undergo special treatment for a virus. These changes can ease symptoms significantly.

Medications may also reduce blood flow into portosystemic collaterals or reduce blood flow within the liver. Your healthcare provider may recommend stopping or switching a medication.

Patients with refractory ascites or GI bleeding may benefit from the surgical placement of shunts between the portal and systemic circulation. For example, a transjugular intrahepatic portosystemic shunt (TIPS) is a shunt placed inside the liver that carries blood directly from the portal veins into the systemic circulation.

A Word From Verywell

The hepatic portal venous system is different from most veins in the body. Those other systemic veins carry blood to the heart, while the portal vein drains blood from the GI tract.

This gives the venous system a unique and important role in how your body works. It also means that it's at risk of becoming ineffective if parts of the GI tract are damaged.

Because of its location, cirrhosis and liver disease have the greatest impact on the portal vein. Keeping your liver healthy is essential to keeping this part of your circulatory system in tip-top shape and avoiding a host of serious medical complications.