The portal vein or hepatic portal vein (HPV) is a

blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...

that carries

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

from the gastrointestinal tract,

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an en ...

and

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

to the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

. 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 hepatic artery proper (also proper hepatic artery) is the artery that supplies the liver and gallbladder. It raises from the common hepatic artery, a branch of the celiac artery. Structure The hepatic artery proper arises from the common ...

. The blood leaves the liver to the heart in the

hepatic veins In human anatomy, the hepatic veins are the veins that drain venous blood from the liver into the inferior vena cava (as opposed to the hepatic portal vein which conveys blood from the gastrointestinal organs to the liver). There are usually thre ...

. The portal vein is not a true

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenat ...

, because it conducts blood to

capillary A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the bod ...

beds in the liver and not directly to the heart. It is a major component of the hepatic portal system, one of only two portal venous systems in the body – with the

hypophyseal portal system The hypophyseal portal system is a system of blood vessels in the microcirculation at the base of the brain, connecting the hypothalamus with the anterior pituitary. Its main function is to quickly transport and exchange hormones between the hypo ...

being the other. The portal vein is usually formed by the confluence of the superior mesenteric, splenic veins, inferior mesenteric, left,

right gastric vein The right gastric vein (pyloric vein) drains blood from the lesser curvature of the stomach into the hepatic portal vein. It is part of the portal circulation. Structure The right gastric vein passes right along the lesser curvature of the stoma ...

s and the

pancreatic vein In human anatomy, the pancreatic veins consist of several small blood vessels which drain the body and tail of the pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in t ...

. 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 Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue rep ...

. In abdominal obesity fats, inflammatory

cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

s and other toxic substances are transported by the portal vein from visceral fat into the liver, leading to hepatic insulin resistance and non-alcoholic fatty liver disease.

Structure

Measuring approximately 8 cm (3 inches) long in adults, the portal vein is located in the

right upper quadrant The human abdomen is divided into quadrants and regions by anatomists and physicians for the purposes of study, diagnosis, and treatment. The division into four quadrants allows the localisation of pain and tenderness, scars, lumps, and other ...

of the abdomen, originating behind the neck of the

. In most individuals, the portal vein is formed by the union of the superior mesenteric vein and the splenic vein. For this reason, the portal vein is occasionally called the ''splenic-mesenteric confluence''. 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 and the left and

s. 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 the portal triad. These vessels ultimately empty into the hepatic sinusoids to supply blood to the liver.

Portacaval anastomoses

The portal venous system has several

anastomoses An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be norm ...

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 veins as well as veins of the

lesser omentum The lesser omentum (small omentum or gastrohepatic omentum) is the double layer of peritoneum that extends from the liver to the lesser curvature of the stomach, and to the first part of the duodenum. The lesser omentum is usually divided into th ...

falciform ligament In human anatomy, the falciform ligament () is a ligament that attaches the liver to the front body wall and divides the liver into the left lobe and right lobe. The falciform ligament is a broad and thin fold of peritoneum, its base being dire ...

, and those draining the

wall.

Function

The portal vein and hepatic arteries form the liver's dual blood supply. Approximately 75% of hepatic blood flow is derived from the portal vein, while the remainder is from the hepatic arteries. Unlike most veins, the portal vein does not drain into the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...

. Rather, it is part of a portal venous system that delivers venous blood into another capillary system, the hepatic sinusoids of the liver. In carrying venous blood from the

gastrointestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

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 The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

. After draining into the liver sinusoids, blood from the liver is drained by the hepatic vein.

Clinical significance

Portal hypertension

Increased blood pressure in the portal vein, called portal hypertension, is a major complication of liver disease, most commonly

. A dilated portal vein (diameter of greater than 13 or 15 mm) is a sign of portal hypertension, with a sensitivity estimated at 12.5% or 40%. On

Doppler ultrasonography Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform imaging of the movement of tissues and body fluids (usually blood), and their relative velocity to the probe. By calculating the frequency shift of ...

, the main portal vein (MPV) peak systolic velocity normally ranges between 20 cm/s and 40 cm/s. A slow velocity of <16 cm/s in addition to dilatation in the MPV are diagnostic of portal hypertension. Clinical signs of portal hypertension include those of chronic liver disease:

ascites Ascites is the abnormal build-up of fluid in the abdomen. Technically, it is more than 25 ml of fluid in the peritoneal cavity, although volumes greater than one liter may occur. Symptoms may include increased abdominal size, increased weight, a ...

, esophageal varices, spider nevi,

caput medusae Caput medusae is the appearance of distended and engorged superficial epigastric veins, which are seen radiating from the umbilicus across the abdomen. The name ''caput medusae'' (Latin for "head of Medusa") originates from the apparent similar ...

, and palmar erythema.

Pulsatility

Doppler ultrasonography of the portal vein in cirrhosis

Portal vein pulsatility can be measured by Doppler ultrasonography. An increased pulsatility may be caused by

, as well as increased right atrial pressure (which in turn may be caused by right heart failure or

tricuspid regurgitation Tricuspid regurgitation (TR), also called tricuspid insufficiency, is a type of valvular heart disease in which the tricuspid valve of the heart, located between the right atrium and right ventricle, does not close completely when the right ventr ...

). Portal vein pulsatility can be quantified by pulsatility indices (PI), where an index above a certain cutoff indicates pathology:

Infection

Pylephlebitis is infection of the portal vein, usually arising from an infectious intra-abdominal process such as diverticulitis.

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.

Additional images

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.

References

External links

* - "Stomach, Spleen and Liver: The Visceral Surface of the Liver" * * * * * {{Authority control Veins of the torso