View source for Portal vein

{{short description|Vein carrying blood from the GI tract, gallbladder, pancreas and spleen to the liver}}
{{about|the vein of the liver|portal veins in general|Portal venous system}}
{{Infobox vein
| Name        = Portal vein
| Latin       = vena portae hepatis
| Image       = Gray591-Portal vein.png
| Caption     = The '''portal vein''' (in light blue) and its tributaries. It is formed by the [[superior mesenteric vein]], inferior mesenteric vein, and [[splenic vein]].  ''Lienal vein'' is an old term for ''splenic vein''.

| Image2      =
| Caption2    =
| DrainsFrom  = [[Gastrointestinal tract]], [[spleen]], [[pancreas]]
| Source      = [[Splenic vein]], [[superior mesenteric vein]], [[inferior mesenteric vein]], [[pancreatic vein]]
| DrainsTo    = [[Liver sinusoid]]
| Artery      =
| System = [[Hepatic portal system]]
}}
The '''portal vein''' or '''hepatic portal vein''' ('''HPV''') is a [[blood vessel]] that carries [[blood]] from the [[gastrointestinal tract]], [[gallbladder]], [[pancreas]] and [[spleen]] to the [[liver]]. This blood contains [[nutrients]] and [[toxins]] extracted from digested contents. Approximately 75% of total liver blood flow is through the portal vein, with the remainder coming from the [[hepatic artery proper]]. The blood leaves the liver to the heart in the [[hepatic veins]].

The portal vein is not a true [[vein]], because it conducts blood to [[capillary]] beds in the liver and not directly to the heart. It is a major component of the [[hepatic portal system]], one of two [[portal venous system]]s in the human body; the other being the [[hypophyseal portal system]]. Some reptiles have an additional [[renal portal system]] not present in mammals.

The portal vein is usually formed by the confluence of the [[superior mesenteric vein|superior mesenteric]], [[splenic vein]]s, [[inferior mesenteric vein|inferior mesenteric]], [[left gastric vein|left]], [[right gastric vein]]s and the [[pancreatic vein]].

Conditions involving the portal vein cause considerable illness and death. An important example of such a condition is elevated [[blood pressure]] in the portal vein. This condition, called [[portal hypertension]], is a major complication of [[cirrhosis]]. In [[abdominal obesity]] fats, inflammatory [[cytokine]]s and other toxic substances are transported by the portal vein from [[Organ (biology)|visceral]] fat into the liver, leading to [[Liver|hepatic]] [[insulin resistance]] and [[metabolic dysfunction–associated steatotic liver disease]].<ref name="pmid23107257">{{cite journal | vauthors=Item F, Konrad D| title=Visceral fat and metabolic inflammation: the portal theory revisited | journal=[[Obesity Reviews]] | volume=13 | issue=Suppl&nbsp;2 | pages=30–39 | year=2012 | doi = 10.1111/j.1467-789X.2012.01035.x | pmid=23107257| s2cid=25169877 | url=https://www.zora.uzh.ch/id/eprint/66137/5/Rev_Portal_Hypothesis-akzeptiertes_Ms.pdf }}</ref><ref name="pmid32818561">{{cite journal | vauthors=Dhawan D, Sharma S | title=Abdominal Obesity, Adipokines and Non-communicable Diseases | journal=[[The Journal of Steroid Biochemistry and Molecular Biology]] | volume=203 | article-number=105737 | year=2020| doi = 10.1016/j.jsbmb.2020.105737 | pmc=7431389 | pmid=32818561}}</ref>

==Structure==
Measuring approximately 8&nbsp;cm (3 inches) long in adults,<ref name="isbn0-7817-7174-9">{{cite book |author1=Harold M Chung |author2=Chung, Kyung Won |title=Gross anatomy |url=https://archive.org/details/brsgrossanatomy00chun_910 |url-access=limited |publisher=Wolters Kluwer Health/Lippincott Williams & Wilkins |location=Philadelphia |year=2008 |pages=[https://archive.org/details/brsgrossanatomy00chun_910/page/n354 208] |isbn=978-0-7817-7174-0 }}</ref> the portal vein is located in the [[right upper quadrant]] of the abdomen, originating behind the neck of the [[pancreas]].<ref name="phtn"/>

In most individuals, the portal vein is formed by the union of the  [[superior mesenteric vein]] and the [[splenic vein]].<ref name="isbn1-55009-364-9">{{cite book |author1=Benjamin L. Shneider |author2=Sherman, Philip M. |title=Pediatric Gastrointestinal Disease |publisher=PMPH-USA |location=Connecticut |year=2008 |page=751 |isbn=978-1-55009-364-3 }}</ref> For this reason, the portal vein is occasionally called the '''''splenic-mesenteric confluence'''''.<ref name="phtn">{{cite book |author1=Plinio Rossi |author2=L. Broglia |title=Portal Hypertension: Diagnostic Imaging and Imaging-Guided Therapy |publisher=Springer |location=Berlin |year=2000 |page=51 |isbn=978-3-540-65797-2 }}</ref> Occasionally, the portal vein also directly communicates with the [[inferior mesenteric vein]], although this is highly variable. Other tributaries of the portal vein include the [[cystic vein|cystic]] and the [[left gastric vein|left]] and [[right gastric vein]]s.<ref name="grays"/> and also pararumbilical vein and prepyloric vein.

{| class="wikitable" style="float:right; border-collapse:collapse" border="1" cellpadding="3"
|+ Tributaries of the hepatic portal vein<ref name="grays">{{cite book |author=Henry Gray |title=Anatomy, Descriptive and Surgical |url=https://archive.org/details/anatomydescript07graygoog |publisher=Lea Brothers |location=Philadelphia |year=1901 |page=619 |edition=16 }}</ref>
|-
|
* [[Splenic vein]]
* [[Superior mesenteric vein]]
* [[Inferior mesenteric vein]]
* [[Left gastric vein|Left]] and [[right gastric vein]]s
* [[Cystic 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 the [[portal triad]]. These vessels ultimately empty into the [[hepatic sinusoid]]s to supply blood to the liver.<ref name="grays"/>

===Portacaval anastomoses===
The [[portal venous system]] has several [[anastomoses]] with the [[systemic venous system]]. In cases of [[portal hypertension]] these anastomoses may become engorged, dilated, or varicosed and subsequently rupture.

===Accessory hepatic portal veins===
Accessory hepatic portal veins are those veins that drain directly into the liver without joining the hepatic portal vein. These include the [[paraumbilical vein]]s as well as veins of the [[lesser omentum]], [[falciform ligament]], and those draining the [[gallbladder]] wall.<ref name="phtn"/>

==Function==
The portal vein and [[hepatic 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.<ref>{{Cite book |last=Cross |first=Simon S. |title=Underwood's Pathology: a Clinical Approach |year=2013 |isbn=978-0-7020-4672-8 |edition=6th |pages=362}}</ref>

Unlike most veins, the portal vein does not drain into the [[heart]]. Rather, it is part of a [[portal venous system]] that delivers venous blood into another [[capillary system]], the [[hepatic sinusoid]]s of the liver. In carrying venous blood from the [[gastrointestinal]] 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 the [[systemic 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 the [[intestines]]. After draining into the liver [[sinusoids]], blood from the liver is drained by the [[hepatic vein]].

==Clinical significance==

===Portal hypertension===
{{main|Portal hypertension}}

Increased [[blood pressure]] in the portal vein, called [[portal hypertension]], is a major complication of liver disease, most commonly [[cirrhosis]].<ref name="isbn0-632-05582-0">{{cite book |author1=Dooley, James |author2=Sherlock, Sheila |title=Diseases of the liver and biliary system |publisher=Blackwell Science |location=Oxford |year=2002 |isbn=978-0-632-05582-1 }}</ref> A dilated portal vein (diameter of greater than 13 or 15&nbsp;mm) is a sign of portal hypertension, with a [[sensitivity and specificity|sensitivity]] estimated at 12.5% or 40%.<ref>{{cite journal|author=Al-Nakshabandi NA|title=The role of ultrasonography in portal hypertension|journal=Saudi J Gastroenterol|volume=12|issue=3|pages=111–7|year=2006|doi=10.4103/1319-3767.29750|pmid=19858596|doi-access=free}}</ref> On [[Doppler ultrasonography]], the main portal vein (MPV) peak systolic velocity normally ranges between 20&nbsp;cm/s and 40&nbsp;cm/s.<ref name="IranpourLall2016">{{cite journal|last1=Iranpour|first1=Pooya|last2=Lall|first2=Chandana|last3=Houshyar|first3=Roozbeh|last4=Helmy|first4=Mohammad|last5=Yang|first5=Albert|last6=Choi|first6=Joon-Il|last7=Ward|first7=Garrett|last8=Goodwin|first8=Scott C|title=Altered Doppler flow patterns in cirrhosis patients: an overview|journal=Ultrasonography|volume=35|issue=1|year=2016|pages=3–12|issn=2288-5919|doi=10.14366/usg.15020|pmid=26169079|pmc=4701371}}</ref> A slow velocity of <16&nbsp;cm/s in addition to dilatation in the MPV are diagnostic of portal hypertension.<ref name="IranpourLall2016"/>

Clinical [[Medical sign|signs]] of portal hypertension include those of chronic liver disease: [[ascites]], [[esophageal varices]], [[spider nevi]], [[caput medusae]], and [[palmar erythema]].<ref name="isbn1-85996-164-9">{{cite book |title=Key Topics in General Surgery |publisher=Informa Healthcare |year=2002 |edition=2 |isbn=978-1-85996-164-3 }}</ref>

===Pulsatility===
[[File:Doppler ultrasonography of the portal vein in cirrhosis.jpg|thumb|[[Doppler ultrasonography]] of the portal vein over 5 seconds, showing peaks of '''max'''imal velocity, as well as points of '''min'''imal velocity.]]

Portal vein pulsatility can be measured by Doppler ultrasonography. An increased pulsatility may be caused by [[cirrhosis]], as well as increased right atrial pressure (which in turn may be caused by right [[heart failure]] or [[tricuspid regurgitation]]).<ref name="IranpourLall2016">{{cite journal|last1=Iranpour|first1=Pooya|last2=Lall|first2=Chandana|last3=Houshyar|first3=Roozbeh|last4=Helmy|first4=Mohammad|last5=Yang|first5=Albert|last6=Choi|first6=Joon-Il|last7=Ward|first7=Garrett|last8=Goodwin|first8=Scott C|title=Altered Doppler flow patterns in cirrhosis patients: an overview|journal=Ultrasonography|volume=35|issue=1|year=2016|pages=3–12|issn=2288-5919|doi=10.14366/usg.15020|pmid=26169079|pmc=4701371}}</ref> Portal vein pulsatility can be quantified by pulsatility indices (PI), where an index above a certain cutoff indicates pathology:

{|class="wikitable"
|+Pulsatility indices (PI)
! Index !! Calculation !! Cutoff
|-
| Average-based || (Max - Min) / Average<ref name="IranpourLall2016"/> || 0.5<ref name="IranpourLall2016"/>
|-
| Max-based || (Max - Min) / Max<ref name="GoncalvesovaVarga2013">{{cite journal|last1=Goncalvesova|first1=E.|last2=Varga|first2=I.|last3=Tavacova|first3=M.|last4=Lesny|first4=P.|title=Changes of portal vein flow in heart failure patients with liver congestion|journal=European Heart Journal|volume=34|issue=suppl 1|year=2013|pages=P627|issn=0195-668X|doi=10.1093/eurheartj/eht307.P627|doi-access=free}}</ref> || 0.5<ref name="GoncalvesovaVarga2013"/><ref name=Dancygier2009>[https://books.google.com/books?id=ZfJN6NS0ZY4C&pg=PA367 Page 367] in: {{cite book|title=Clinical Hepatology: Principles and Practice of Hepatobiliary Diseases|volume=1|author=Henryk Dancygier|publisher=Springer Science & Business Media|year=2009|isbn=978-3-540-93842-2}}</ref> - 0.54<ref name=Dancygier2009/>
|}

===Infection===
{{main|Pylephlebitis}}

[[Pylephlebitis]] is infection of the portal vein, usually arising from an infectious intra-abdominal process such as [[diverticulitis]].<ref name="pmid8589130">{{cite journal |vauthors=Plemmons RM, Dooley DP, Longfield RN |title=Septic thrombophlebitis of the portal vein (pylephlebitis): diagnosis and management in the modern era |journal=Clin. Infect. Dis. |volume=21 |issue=5 |pages=1114–20 |date=November 1995 |pmid=8589130 |doi= 10.1093/clinids/21.5.1114}}</ref><ref name="pmid8488411">{{cite journal |vauthors=Perez-Cruet MJ, Grable E, Drapkin MS, Jablons DM, Cano G |title=Pylephlebitis associated with diverticulitis |journal=South. Med. J. |volume=86 |issue=5 |pages=578–80 |date=May 1993 |pmid=8488411 |doi= 10.1097/00007611-199305000-00020}}</ref>

===Portal venous gas===
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.<ref name="Li">{{cite journal |last1=Li |first1=Z |last2=Su |first2=Y |last3=Wang |first3=X |last4=Yan |first4=H |last5=Sun |first5=M |last6=Shu |first6=Z |title=Hepatic portal venous gas associated with colon cancer: A case report and literature review. |journal=Medicine |date=December 2017 |volume=96 |issue=50 |article-number=e9352 |doi=10.1097/MD.0000000000009352 |pmid=29390409|pmc=5815821 }}</ref>

==Additional images==
<gallery>
File:Gray476.png|Human embryo with heart and anterior body-wall removed to show the sinus venosus and its tributaries
File:Gray1093.png|Section across the [[portal triad]] of the pig
File:Gray1090.png|Longitudinal section of a small portal vein and canal
File:Slide6gen.JPG|Hepatic portal vein. Plastination technique.
File:Slide22Gre.JPG|Hepatic portal vein. Abdominal cavity. Deep dissection.
File:Slide14CHA.JPG|Hepatic portal vein. Visceral surface of liver.
</gallery>

==References==
{{Reflist}}

==External links==
* {{SUNYAnatomyLabs|38|12|01|09}}—"Stomach, Spleen and Liver: The Visceral Surface of the Liver"
* {{SUNYAnatomyImage|7|9|59}}
* {{SUNYAnatomyImage|8|5|65}}
* {{SUNYAnatomyImage|8|6|97}}
* {{ViennaCrossSection|pembody/body8a}}
* {{DartmouthHumanAnatomy|figures/chapter_30/30-2.HTM}}

{{Cardiovascular_system}}
{{Veins of the abdomen and pelvis}}
{{Authority control}}

[[Category:Veins of the torso]]