What Is the Portal Venous System?

The portal venous system, otherwise known as the hepatic portal system, is part of the human circulatory system. It is comprised of the hepatic portal vein and its branches. This system plays a small in the body’s circulation.

Directing blood from some parts of the gastrointestinal tract to the liver is done by the portal venous system. The section of the gastrointestinal tract that this system is responsible for extends from the lower esophagus section to the upper anal canal section. Venous drainage from the pancreas and the spleen are also included.

Portal blood that passes through this system has a lower perfusion pressure and partial gas pressure of oxygen. This is because the liver receives both oxygenated and deoxygenated blood. Blood flow goes through the portal vein and its branches into cavities in between the hepatocytes called sinusoids. The hepatic artery provides oxygen to the hepatocytes.

After the oxygenated blood from the hepatic vein and the blood from the portal vein mix in the sinusoids, it travels into a central vein and then drains into the hepatic vein. The mixed blood drains into the inferior vena cava. Through this pathway, the liver is provided with about 40 percent of the oxygen it requires in an average total of about 25 percent of the blood that flows through. The remaining amount of blood that goes to the liver from the portal venous system comes from the deoxygenated blood provided by the portal vein.

There are four main large veins that are part of the venous system. The superior mesmenteric vein and the splenic vein join to make the hepatic portal vein. For some people, the inferior mesenteric vein connects to the splenic vein. In other cases, the inferior mesenteric vein connects to either the superior mesenteric vein or the portal vein.

The liver processes and filters things before they travel to the heart. It is important for doctors to consider how the portal venous system functions when prescribing medication. Due to how the liver functions, it essentially detoxifies the blood, which can negate many medications. For this reason, different methods of delivery are used to bypass the portal system when it is necessary to reach the heart fully active. An example includes nitroglycerin given to treat heart conditions, which is delivered under the tongue to bypass the portal system.