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 awa ...
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,
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 ...
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 i ...
. This blood contains
nutrients
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...
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
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 oxygenated ...
, 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
In human anatomy, the hepatic portal system is the system of veins comprising the hepatic portal vein and its tributaries. It is also called the portal venous system (although it is not the only example of a portal venous system) and splanchnic ...
, one of only two
portal venous system
In the circulatory system of animals, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are con ...
s 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 hy ...
being the other.
The portal vein is usually formed by the confluence of the
superior mesenteric,
splenic veins,
inferior mesenteric,
left,
right gastric veins 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
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "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
Abdominal obesity, also known as central obesity and truncal obesity, is a condition when excessive visceral fat around the stomach and abdomen has built up to the extent that it is likely to have a negative impact on health. Abdominal obesity h ...
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 au ...
s and other toxic substances are transported by the portal vein from
visceral
In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a f ...
fat into the liver, leading to
hepatic insulin resistance and
non-alcoholic fatty liver disease
Non-alcoholic fatty liver disease (NAFLD), also known as metabolic (dysfunction) associated fatty liver disease (MAFLD), is excessive fat build-up in the liver without another clear cause such as alcohol use. There are two types; non-alcoholic ...
.
Structure
Measuring approximately 8 cm (3 inches) long in adults,
the portal vein is located in the
right upper quadrant of the abdomen, originating behind the neck of the
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 ...
.
In most individuals, the portal vein is formed by the union of the
superior mesenteric vein
In human anatomy, the superior mesenteric vein (SMV) is a blood vessel that drains blood from the small intestine (jejunum and ileum). Behind the neck of the pancreas, the superior mesenteric vein combines with the splenic vein to form the hepa ...
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
In human anatomy, the inferior mesenteric vein (IMV) is a blood vessel that drains blood from the large intestine. It usually terminates when reaching the splenic vein, which goes on to form the portal vein with the superior mesenteric vein (SM ...
, although this is highly variable. Other tributaries of the portal vein include the
cystic and the
left and
right gastric veins.
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
In histology (microscopic anatomy), the lobules of liver, or hepatic lobules, are small divisions of the liver defined at the microscopic scale. The hepatic lobule is a building block of the liver tissue, consisting of a portal triad, hepatocy ...
. These vessels ultimately empty into the
hepatic sinusoid
A liver sinusoid is a type of capillary known as a sinusoidal capillary, discontinuous capillary or sinusoid, that is similar to a fenestrated capillary, having discontinuous endothelium that serves as a location for mixing of the oxygen-rich bl ...
s to supply blood to the liver.
Portacaval anastomoses
The
portal venous system
In the circulatory system of animals, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are con ...
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
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, t ...
. 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
In the course of the round ligament of liver, small veins (paraumbilical) are found which establish an anastomosis between the veins of the anterior abdominal wall and the hepatic portal, hypogastric, and iliac veins.
The best marked of these sm ...
s as well as veins of the
lesser omentum,
falciform ligament, and those draining the
gallbladder 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 (biology), 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 ca ...
. Rather, it is part of a
portal venous system
In the circulatory system of animals, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are con ...
that delivers venous blood into another
capillary system
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 body: ...
, the
hepatic sinusoid
A liver sinusoid is a type of capillary known as a sinusoidal capillary, discontinuous capillary or sinusoid, that is similar to a fenestrated capillary, having discontinuous endothelium that serves as a location for mixing of the oxygen-rich bl ...
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
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, t ...
. 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
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 body: ...
, blood from the liver is drained by the
hepatic vein
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 thr ...
.
Clinical significance
Portal hypertension
Increased
blood pressure
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure ...
in the portal vein, called
portal hypertension, is a major complication of liver disease, most commonly
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 ...
.
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 a ...
, 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,
esophageal varices,
spider nevi
A spider angioma or spider naevus (plural: spider naevi), also nevus araneus, is a type of telangiectasis (swollen, spider-like blood vessels on the skin) found slightly beneath the skin's surface, often containing a central red spot and deep redd ...
,
caput medusae, and
palmar erythema
Palmar erythema is reddening of the palms at the thenar and hypothenar eminences.James, William; Berger, Timothy; Elston, Dirk (2005). ''Andrews' Diseases of the Skin: Clinical Dermatology''. (10th ed.). Saunders. .
Causes
It is associated with va ...
.
Pulsatility
Portal vein pulsatility can be measured by Doppler ultrasonography. An increased pulsatility may be caused by
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 ...
, as well as increased right atrial pressure (which in turn may be caused by right
heart failure
Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...
or
tricuspid regurgitation).
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
In histology (microscopic anatomy), the lobules of liver, or hepatic lobules, are small divisions of the liver defined at the microscopic scale. The hepatic lobule is a building block of the liver tissue, consisting of a portal triad, hepatocy ...
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"
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Veins of the torso