A portal vein or portal vein (Latin: Vena portae ) is a vein that branches off again into capillary areas. In mammals , there are two in birds and reptiles three Pfortadern:
- Hepatic portal vein ( Vena portae hepatis ), usually referred to only as portal vein ( Vena portae )
- Pituitary portal veins ( Venae portales hypophysiales )
- Renal portal vein ( Vena portalis renalis ): only in birds, reptiles and amphibians
All portal veins have in common that they pass substances released into the blood from a capillary area in high concentration to the capillary of a target organ.
Portal (liver) vein
The portal vein ( Vena portae ) collects the blood from the unpaired abdominal organs ( stomach , small intestine , large intestine , parts of the rectum , pancreas , spleen ) and delivers it to the liver .
The blood of the portal vein is low in oxygen and rich in nutrients (from the digestive organs) or metabolic products (e.g. bilirubin ) after eating . The veins of the organs mentioned unite to form the portal vein, which flows into the liver at the porta hepatic along with the hepatic artery ( arteria hepatica propria ). In the capillaries of the liver, the liver sinusoids , the nutrient-rich blood from the portal vein mixes with the oxygen-rich blood from the hepatic artery and is thus available for the metabolism of the liver cells.
The task of the portal vein is to supply the liver with the nutrients and possible toxins that have been developed in the intestine. The latter are largely metabolized in the liver before they enter the bloodstream. This can also have the undesirable effect that drugs may be broken down to a large extent in the liver before they can reach the target organ via the bloodstream (→ first-pass effect ). Certain substances that are released from the liver via the gallbladder into the intestinal lumen can also pass through the portal vein system several times before they enter the large bloodstream (→ enterohepatic circulation ). In order to bypass the portal vein system when administering medication, these can be administered parenterally .
The portal vein lies horizontally behind the pancreas and then ascends to the upper right in the ligamentum hepatoduodenale into the porta hepatic ( porta hepatis ). It arises embryonically from the left yolk vein ( vena vitellina sinistra ). The portal vein collects blood from:
- the vv. gastricae dextrae and sinistrae (gastric veins)
- the pyloric vein (vein of the gastric gatekeeper )
- the cystic vein
- the paraumbilical veins
- the superior mesenteric vein (superior intestinal vein), known in animals as the cranial mesenteric vein (anterior intestinal vein)
- the inferior mesenteric vein (lower intestinal vein), known in animals as the caudal mesenteric vein (posterior intestinal vein)
- the vein splenic (splenic vein; Veterinary Anatomy splenic vein , in human anatomy outdated name, in the hospital but quite common)
The confluence of the splenic vein and the superior mesenteric vein is the actual beginning of the portal vein and is called the confluens. After entering the hepatic portal, the portal vein divides early into a branch to the right and left lobes of the liver and then branches into further small branches up to the liver sinusoids. The blood of the liver leaves the organ from the central veins via the hepatic veins in the direction of the inferior vena cava and the right anterior chamber (this is no longer part of the portal vein system, however).
Nutrients and other substances absorbed via the intestine reach the liver via the portal vein, where they are partially metabolized before they enter the somatic bloodstream. In some cases, substances are also released back into the intestine via the bile. From here they can be reabsorbed and returned to the liver via the portal vein. This phenomenon is known as the enterohepatic cycle . This can be important for drugs, among other things.
Parasites can get through the portal vein directly into the liver, and thus into the first capillary system , and insert there. In order to reproduce, some of them have adapted directly to the intestinal, portal vein, liver and gallbladder system (see the Diseases section ).
The hepatic portal vein is a potential transport route for pathogens to the liver. As an example of the might parasites of humans counting fox tapeworm serve the larva sets in which the liver of an intermediate host, and thereby the alveolar hydatid disease triggers. Also flukes attack the liver in this way. Depending on the type, a pathogen can settle here, migrate to the gallbladder or float to other organs via the blood.
If the blood is congested in the portal vein or liver, the portal vein circulation is bypassed. The blood from the abdominal organs can no longer take its natural route back to the heart via the portal vein, liver and inferior vena cava ( inferior vena cava ) , but instead gives way to other veins, and portacaval anastomoses are formed . Possible routes here are the veins of the esophagus ( esophageal varices ), deep and superficial veins of the abdominal and chest wall ( caput medusae ) and veins of the rectum.
Thrombosis of the portal vein
In addition to portal hypertension, thrombosis of the portal vein, for example in liver cirrhosis or liver cancer , can rarely be found.
Air in the portal vein
In very rare cases, air can be detected in the portal vein in severe, mostly fatal intestinal diseases, for example in necrotizing enterocolitis or in the rare gastric volvulus .
Persistent ductus venosus
The ductus venosus is a physiological portacaval anastomosis between the portal vein and the lower (in animals, posterior) vena cava in the fetus . It usually closes before or shortly after birth. If this does not occur, the blood (and thus also the pollutants absorbed in the intestine) gets directly into the body's circulation, bypassing the liver.
- Indirect splenoportography (indirect vascular imaging via the splenic artery)
- CT and MRI
- Width about 8 to 15 mm
- Length about 4 to 5 cm
- Flow rate about 13 to 23 cm / s
- Pressure 5–20 mmHg (difficult to measure)