| Portal vein | |
|---|---|
 Theportal vein (in light blue) and its tributaries. It is formed by thesuperior mesenteric vein, inferior mesenteric vein, andsplenic vein.Lienal vein is an old term forsplenic vein. | |
| Details | |
| System | Hepatic portal system |
| Drains from | Gastrointestinal tract,spleen,pancreas |
| Source | Splenic vein,superior mesenteric vein,inferior mesenteric vein,pancreatic vein |
| Drains to | Liver sinusoid |
| Identifiers | |
| Latin | vena portae hepatis |
| MeSH | D011169 |
| TA98 | A12.3.12.001 |
| TA2 | 5092 |
| FMA | 50735 |
| Anatomical terminology | |
Theportal vein orhepatic portal vein (HPV) is ablood vessel that carriesblood from thegastrointestinal tract,gallbladder,pancreas andspleen to theliver. This blood containsnutrients andtoxins extracted from digested contents. Approximately 75% of total liver blood flow is through the portal vein, with the remainder coming from thehepatic artery proper. The blood leaves the liver to the heart in thehepatic veins.
The portal vein is not a truevein, because it conducts blood tocapillary beds in the liver and not directly to the heart. It is a major component of thehepatic portal system, one of twoportal venous systems in the human body; the other being thehypophyseal portal system. Some reptiles have an additionalrenal portal system not present in mammals.
The portal vein is usually formed by the confluence of thesuperior mesenteric,splenic veins,inferior mesenteric,left,right gastric veins and thepancreatic vein.
Conditions involving the portal vein cause considerable illness and death. An important example of such a condition is elevatedblood pressure in the portal vein. This condition, calledportal hypertension, is a major complication ofcirrhosis. Inabdominal obesity fats, inflammatorycytokines and other toxic substances are transported by the portal vein fromvisceral fat into the liver, leading tohepaticinsulin resistance andmetabolic dysfunction–associated steatotic liver disease.[1][2]
Measuring approximately 8 cm (3 inches) long in adults,[3] the portal vein is located in theright upper quadrant of the abdomen, originating behind the neck of thepancreas.[4]
In most individuals, the portal vein is formed by the union of thesuperior mesenteric vein and thesplenic vein.[5] For this reason, the portal vein is occasionally called thesplenic-mesenteric confluence.[4] Occasionally, the portal vein also directly communicates with theinferior mesenteric vein, although this is highly variable. Other tributaries of the portal vein include thecystic and theleft andright gastric veins.[6] and also pararumbilical vein and prepyloric vein.
Immediately before reaching the liver, the portal vein divides into right and left. It ramifies further, forming smaller venous branches and ultimately portal venules. Each portal venule courses alongside a hepatic arteriole and the two vessels form the vascular components of theportal triad. These vessels ultimately empty into thehepatic sinusoids to supply blood to the liver.[6]
Theportal venous system has severalanastomoses with thesystemic venous system. In cases ofportal hypertension these anastomoses may become engorged, dilated, or varicosed and subsequently rupture.
Accessory hepatic portal veins are those veins that drain directly into the liver without joining the hepatic portal vein. These include theparaumbilical veins as well as veins of thelesser omentum,falciform ligament, and those draining thegallbladder wall.[4]
The portal vein andhepatic arteries form the liver's dual blood supply, with 90% of hepatic blood flow and 70% of oxygen supplied by the portal vein, and the remainder by hepatic arteries. Due to its double blood supply, the liver is far less affected by vascular disease compared to other major internal organs.[7]
Unlike most veins, the portal vein does not drain into theheart. Rather, it is part of aportal venous system that delivers venous blood into anothercapillary system, thehepatic sinusoids of the liver. In carrying venous blood from thegastrointestinal tract to the liver, the portal vein accomplishes two tasks: it supplies the liver with metabolic substrates and it ensures that substances ingested are first processed by the liver before reaching thesystemic circulation. This accomplishes two things. First, possible toxins that may be ingested can be detoxified by the hepatocytes before they are released into the systemic circulation. Second, the liver is the first organ to absorb nutrients just taken in by theintestines. After draining into the liversinusoids, blood from the liver is drained by thehepatic vein.
Increasedblood pressure in the portal vein, calledportal hypertension, is a major complication of liver disease, most commonlycirrhosis.[8] A dilated portal vein (diameter of greater than 13 or 15 mm) is a sign of portal hypertension, with asensitivity estimated at 12.5% or 40%.[9] OnDoppler ultrasonography, the main portal vein (MPV) peak systolic velocity normally ranges between 20 cm/s and 40 cm/s.[10] A slow velocity of <16 cm/s in addition to dilatation in the MPV are diagnostic of portal hypertension.[10]
Clinicalsigns of portal hypertension include those of chronic liver disease:ascites,esophageal varices,spider nevi,caput medusae, andpalmar erythema.[11]
Portal vein pulsatility can be measured by Doppler ultrasonography. An increased pulsatility may be caused bycirrhosis, as well as increased right atrial pressure (which in turn may be caused by rightheart failure ortricuspid regurgitation).[10] Portal vein pulsatility can be quantified by pulsatility indices (PI), where an index above a certain cutoff indicates pathology:
| Index | Calculation | Cutoff |
|---|---|---|
| Average-based | (Max - Min) / Average[10] | 0.5[10] |
| Max-based | (Max - Min) / Max[12] | 0.5[12][13] - 0.54[13] |
Pylephlebitis is infection of the portal vein, usually arising from an infectious intra-abdominal process such asdiverticulitis.[14][15]
Hepatic portal venous gas is a rare finding on radiological exams. Gas is shown to enter the portal venous system. It is most commonly caused by intestinal ischemia but has also been associated with colon cancer.[16]
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