What is the portal vein circulation?
The portal vein circulation is a part of the large blood circulation. The main vessel is the portal vein (Vena portae hepatis). It transports deoxygenated blood from the stomach, intestines and other abdominal organs to the liver. The blood contains numerous substances that have been absorbed from the digestive organs. These include nutrients, but also active ingredients from medications, for example.
What is the portal vein system for?
The reason is that the liver is the central metabolic organ: When the blood flows through the capillary network of the liver, the substances absorbed in the intestine can be processed immediately – they are stored, transformed or broken down as required.
Detoxification and drug metabolism
After being absorbed in the digestive tract, various drugs are also first transported to the liver via the portal circulation. Part of the active ingredients is metabolized here, and only the remainder continues to pass through the bloodstream and can distribute itself throughout the body and exert its effect (first-pass effect). In order to circumvent the portal vein circulation and thus this first-pass effect, some drugs are therefore introduced directly into the bloodstream (as infusion or injection).
The portal vein circulation is also used by the bile produced in the liver: It passes through the bile ducts into the gall bladder (storage site) and on to the intestine, where it supports fat digestion. Later, much of the bile is reabsorbed back into the blood through the intestinal wall and returned to the liver via the portal vein (enterohepatic circulation).
Problems in the area of the portal vein circulation
Possible intrahepatic causes include acute or chronic liver inflammation (hepatitis), liver cirrhosis, liver tumors and sarcoidosis. Posthepatic causes of blood backpressure and thus an increase in pressure in the portal circulation include cardiac diseases such as right heart failure or “armored heart” (pericarditis constrictiva).
