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Does the hepatic portal system form capillary beds?

Does the hepatic portal system form capillary beds?



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Does the hepatic portal system form capillary beds? If so, is the capillary bed coordinated with that of arterial capillaries?

What review paper might I look in?


In anatomy, a "portal circulation" is simply when you have a capillary bed that is interposed between two venous circulations BEFORE blood flows back to the heart. There are a couple of places in the body where this occurs, including the liver (hepatic portal system) and the pituitary (hypophyseal portal system).

To answer your question… yes, the hepatic portal circulation drains into the liver sinusoids, which is one large capillary circulation.

The hepatic arteries and portal vein give off branches that make up the portal triad which delivers blood (both arterial and venous blood) to the functional units of the liver which are the hepatic lobules.

The hepatic portal system drains into the liver and forms a highly fenestrated network of capillary beds within the liver parenchyma. In the case of the hepatic portal circulation, the flow through the liver sinusoids is considered this capillary bed. In humans, the flow of blood that makes up the hepatic portal circulation is mostly venous blood from the gastrointestinal tract. This allows blood to flow through the liver for clearance of substances like drugs and hormones before those substances reach the peripheral circulation. Specifically, arterial blood flows to the majority of the stomach, small intestine and colon from the celiac, superior and inferior mesenteric arteries. This arterial blood flows through the capillary beds in the mesenteric circulation (i.e. the capillary beds around the intestinal enterocytes) and then into the major veins that drain the intestinal tract. There are two major veins that drain the intestinal tract, the superior and inferior mesenteric veins. The inferior mesenteric vein drains into the splenic vein and then the splenic vein and superior mesenteric veins merge to form the portal vein of the liver. Once blood flows into the portal vein it flows through the hepatic sinusoids (another capillary bed) before flowing out of the hepatic veins into the inferior vena cava, and then back into the heart.


The figure below is a picture of the intestinal veins from Gray's Anatomy (wikipedia) that form the hepatic portal vein, the superior and inferior mesenteric as well as the splenic vein. In the figure the older term lienal vein is used instead of splenic vein. The latin word for spleen is lineal.



The picture below is a schematic of the hepatic lobule that receives its blood from a portal triad. In the center of the lobule is the "central vein". The blood flows from the portal triad to the central vein, and then the central veins coalesce to form the hepatic veins (which then drain into the inferior vena cava). The picture below is available from this website, along with some other text and picture for more information.


And another nice picture from wikipedia on "hepatic lobules". .


As for a "freely available review" that you asked for, I can't find any with better pictures from PubMed that what is already in this answer.


This picure is from Junqueira histology book:

as it shows a branch of hepatic portal vain and a branch of hepatic artery form hepatic sinusoid which is some sort of capillaries. hope it helps :)


The Hepatic Portal System

When blood passes through the gastrointestinal tract, it absorbs numerous substances from food. This may include vital nutrients (except fats that enter the blood via the lymphatic system), but also dangerous and harmful foreign particles and pathogens.

One of the important functions of the liver is the detoxification of the body. The blood carries these many substances from the gastrointestinal tract directly into the liver where they undergo biotransformation.

This way, harmful substances can be rapidly neutralized. In pharmacology, the presence of a first-pass effect must be taken into account when administering oral medications, and drug dosage must be adjusted to compensate for this effect. If a drug dosage is too low, the majority of the drug is metabolized in the liver and is no longer effective.

The liver must filter blood from the spleen as well since it is well known that red blood cells are degraded here. Their constituents accumulate in the blood and must be completely disassembled and recycled in the liver.


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What veins make up the hepatic portal system?

It is formed by the superior mesenteric vein, inferior mesenteric vein, and splenic vein. Lienal vein is an old term for splenic vein. The portal vein or hepatic portal vein is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver.

Secondly, what is the portal venous system? The portal venous system refers to the vessels involved in the drainage of the capillary beds of the GI tract and spleen into the capillary bed of the liver. Blood flow to the liver is unique in that it receives both oxygenated and deoxygenated blood.

Likewise, what makes up the hepatic portal system?

The hepatic portal system is a series of veins that carry blood from the capillaries of the stomach, intestine, spleen, and pancreas to capillaries in the liver. Its main function is to deliver de-oxygenated blood to the liver to be detoxified further before it returns to the heart.

What is the significance of hepatic portal system in the circulatory system?

circulatory system They are called the hepatic (liver) and renal (kidneys) portal systems. The hepatic system is important because it collects blood from the intestine and passes it to the liver, the centre for many chemical reactions concerned with the absorption of food into the body and the control of substances&hellip


The Small Intestine

Digestion within the small intestine produces a mixture of disaccharides, peptides, fatty acids, and monoglycerides. The final digestion and absorption of these substances occurs in the villi, which line the inner surface of the small intestine.

This scanning electron micrograph (courtesy of Keith R. Porter) shows the villi carpeting the inner surface of the small intestine.

  • more stem cells
  • Paneth cells, which secrete antimicrobial peptides [Link to discussion] that suppress the concentration of bacteria in the small intestine.
  • cells that migrate up the surface of the villus while differentiating into
      (the majority). They are responsible for digestion and absorption.
  • goblet cells, which secrete mucus
  • endocrine cells, which secrete a variety of hormones
    Link to Gut Hormones.

The continuous production of new epithelial cells replace older cells that after about 5 days die by apoptosis.

The villi increase the surface area of the small intestine to many times what it would be if it were simply a tube with smooth walls. In addition, the apical (exposed) surface of the epithelial cells of each villus is covered with microvilli (also known as a "brush border"). Thanks largely to these, the total surface area of the intestine is approximately 40 square meters, some 20 times the surface area of the exterior of the body (

The electron micrograph (courtesy of Dr. Sam L. Clark) shows the microvilli of a mouse intestinal cell.

  • aminopeptidases attack the amino terminal (N-terminal) of peptides producing amino acids.
  • disaccharidases These enzymes convert disaccharides into their monosaccharide subunits.
    • maltase hydrolyzes maltose into glucose.
    • sucrase hydrolyzes sucrose (common table sugar) into glucose and fructose.
    • lactase hydrolyzes lactose (milk sugar) into glucose and galactose.

    Humans with a rare genetic inability to form microvilli die of starvation.


    Portal Triad Anatomy

    See portal triad for discussion of misnomer mouseover for labeled slide references. The term however can be considered a misnomer since it contains other structures as well.

    The Liver Lobes Ligaments Vasculature Teachmeanatomy

    Inflammation is confined to the portal trials hirschfield 2011.

    Portal triad anatomy. The hepatic artery the hepatic portal vein and the hepatic ducts or bile ducts. Interlobular bile ducts drain into larger ones as septal or trabecular ducts. A portal triad is an arrangement in the liver which consists of a hepatic artery a portal vein and a bile duct.

    Each portal triad consists of connective tissue in which are embedded a branch of the portal vein arterioles and interlobular bile ducts in addition to lymphatics and nerves. Portal triads may contain a small number of lymphocytes. It can refer both to the largest branch of each of these vessels running inside the hepatoduodenal ligament and to the smaller branches of these vessels inside the liver.

    The portal triad is an area at the liver named after its triangular shape and its three major components. Injured bile ducts surrounded by a dense infiltrate of mononuclear cells most of which are lymphocytes these florid asymmetric destructive lesions of interlobular bile ducts are irregularly scattered throughout the portal triads and often seen only on large surgical biopsies of the liver in which adequate representation of small bile ducts occurs. The bile duct carries bile products away from the hepatocytes to the larger ducts and gall bladder.

    Portal triad portal triads are composed of three major tubes. Branches of the hepatic artery carry oxygenated blood to the hepatocytes while branches of the portal vein carry blood with nutrients from the small intestine. The misnomer portal triad traditionally has included only the first three structures and was named before lymphatic vessels were discovered in the structure.

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    The Large Intestine (colon)

    The large intestine receives the liquid residue after digestion and absorption are complete. This residue consists mostly of water as well as any materials that were not digested. The colon contains an enormous (

    4 13 ) population of microorganisms. Our bodies consist of about the same number (

    3 13 ) of cells. Most of the species live there perfectly harmlessly that is, they are commensals. Some are actually beneficial as they synthesize vitamins and digest polysaccharides for which we have no enzymes (providing an estimated 10% of the calories we acquire from our food).

    Most of the bacteria belong to the Firmicutes and Bacteroidetes (although used as an indicator of water pollution by feces, E. coli is actually a minor component). In both obese mice (ob/ob) and humans, the relative proportion of Bacteroidetes declines and, in mice at least, the efficiency with which residual food is absorbed increases. Putting humans on a diet causes them to regain the normal proportion of Bacteroidetes. Why this relationships exists remains to be discovered. Bacteria flourish to such an extent that as much as 50% of the dry weight of the feces may consist of bacterial cells.

    Reabsorption of water is the chief function of the large intestine. The large amounts of water secreted into the stomach and small intestine by the various digestive glands must be reclaimed to avoid dehydration. If the large intestine becomes irritated, it may discharge its contents before water reabsorption is complete causing diarrhea. On the other hand, if the colon retains its contents too long, the fecal matter becomes dried out and compressed into hard masses causing constipation.


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    Portal Hypertension

    The liver serves many purposes within the body from making carbohydrates, proteins and fats to synthesizing bile to help digest food. Because of this, the liver requires a significant blood supply. As opposed to other organs in the body, the majority of this blood supply (75%) comes from the venous system through the portal system. Blood vessels from the stomach, small intestine, pancreas, and spleen converge and form the portal vein delivering nutrients and chemical building blocks to the liver. Once in the liver, the portal vein and hepatic artery (which accounts for 25% of the liver's blood supply) come together to form sinusoids, spaces where the blood is filtered. From there, blood makes its way to the vena cava, the largest vein in the body to return to the heart.

    Portal hypertension describes elevated pressure within the portal system, including the portal vein and the tributary veins that drain into it. The pressure within the portal system is not normally measured and is not an issue except if an illness or disease occurs that makes it difficult for blood to flow through the liver tissue. This damming effect increases pressure within the portal venous system and causes potential problems with liver function. It is the onset of symptoms associated with liver disease that might cause the health care professional to look for the presence of portal hypertension.

    What causes portal hypertension?

    Portal hypertension occurs when there is an obstruction of blood flow through the liver, and pressure rises within the portal vein. This obstruction can be intrahepatic (intra=within +hepatic=liver), pre-hepatic (pre=before) or post- hepatic (post=after).

    Intrahepatic causes of portal hypertension

    Intrahepatic causes of portal hypertension include cirrhosis and hepatic fibrosis or scarring. A wide variety of illnesses are implicated as the cause of portal hypertension. Examples include the following:

      , and C infections, (NASH, non-alcoholic steatohepatitis),
  • Wilson's disease, an abnormality of copper metabolism, (iron overload), excess iron buildup , a hardening of the bile ducts
  • Biliary atresia, poorly formed bile ducts
  • Parasite infections such as schistosomiasis
  • Pre-hepatic causes of portal hypertension

    • Portal vein thrombosis or blood clots within the portal vein
    • Congenital portal vein atresia or failure of the portal vein to develop

    Post-hepatic causes of portal hypertension

    Post-hepatic causes are due to obstruction of blood flow from the liver to the heart and can include:

    • Hepatic vein thrombosis
    • Inferior vena cava thrombosis
    • Restrictive pericarditis, where the lining of the heart stiffens and does not allow the heart to relax and expand when blood returns to it. Causes may include tuberculosis, fungal infections, tumors, connective tissue disorders (for example, scleroderma), and complications from radiation therapy.

    Portal Hypertension Symptoms & Signs

    Portal hypertension is a condition characterized by elevated pressure within the portal venous system, including the portal vein that carries blood to the liver and its smaller branches.

    Signs and symptoms of portal hypertension are related to the backup of pressure within the venous system. These can include varices, or enlarged veins, in the esophagus or stomach. Varices can cause vomiting blood or black, tarry stool. Other associated symptoms can include

    • ascites,
    • confusion,
    • lethargy,
    • splenomegaly or enlargement of the spleen,
    • anemia,
    • thrombocytopenia, and
    • decreased white blood cell counts.

    What are the symptoms of portal hypertension?

    When blood cannot easily flow through the liver architecture (from portal vein to sinusoids to hepatic vein to vena cava), it tries to bypass the portal system, using the systemic venous system to return to the heart. Symptoms of portal hypertension are due to the complications of decreased blood flow through the liver, and from increased pressure within the veins where blood is shunted.

    • Varices describe enlarged veins. Blood, meant for the portal system, is diverted to and gathers in other veins as it makes its way to the heart. These varices can occur in the esophagus, stomach, around the umbilicus and in the anus and rectum.
    • Esophageal and gastric varices are at risk for life-threatening bleeding and can have signs and symptoms with vomiting blood and blood in the stool. Melena describes black, tarry stool that is the result of upper gastrointestinal bleeding.
    • Ascites describes abnormal fluid collection within the peritoneum (the sac that contains the intestines within the abdominal cavity) and is due to a combination of factors, including increased pressure in the portal system and decrease protein in the body. The liver produces the body's protein portal hypertension and the underlying liver disease decrease its ability to function.
    • Hepatic encephalopathy is another complication of liver disease, causing confusion and lethargy due to the buildup of waste products and the inability of the liver to adequately filter them.
    • Splenomegaly or enlargement of the spleen. Because of portal hypertension, blood backs up, and this also can trap the components of blood (red blood cells, white blood cells, and platelets) within the spleen causing anemia and thrombocytopenia (low platelet count in the bloodstream).
    • Decreased white blood cell counts increase the risk of general infection. Spontaneous bacterial peritonitis is an infection within the peritoneal sac within the abdomen, and is seen as a consequence of long-standing portal hypertension.

    SLIDESHOW

    How is the diagnosis of portal hypertension made?

    Portal hypertension usually is diagnosed well after the process has begun in the body, and only after a complication occurs. When a patient develops ascites or has gastrointestinal bleeding, the health care professional will look for potential causes, including portal hypertension.

    Once the diagnosis is a possibility, it can be confirmed by blood tests, X-rays, CT or MRI, and endoscopy. Pressures within the portal vein are not routinely measured except in specific situations (see TIPS procedure).

    What is the treatment for portal hypertension?

    Treatment for portal hypertension is often directed at preventing complications. This includes treating the underlying cause and avoidance of alcohol. Because of the risk of further liver damage, over-the-counter medications that contain acetaminophen (Tylenol, Panadol, for example) should also be avoided.

    Dietary restrictions include limiting salt to prevent further ascites fluid accumulation. Protein may also be restricted, since increased protein load can overwhelm the liver's ability to synthesize it and may lead to hepatic encephalopathy.

    Medications such as beta-blockers and nitroglycerin may be appropriate to decrease pressure within the portal system. Lactulose may be prescribed as a treatment for hepatic encephalopathy.

    Endoscopy may be required to band or tie off varices in the esophagus to prevent catastrophic and life-threatening bleeding.

    A TIPS procedure (transjugular intrahepatic portosystemic shunt) may be an option to decrease the pressure within the portal system. An interventional radiologist attempts to place a tube that connects the portal vein with the hepatic vein. This may decrease the pressure within the liver and may also reduce pressure within the veins of the stomach and esophagus, hopefully decreasing the risk of bleeding.

    If portal hypertension and liver dysfunction become bad enough, liver transplantation may be necessary.


    Examples of hepatic portal system in the following topics:

    Blood Supply to the Liver

    • In the hepaticportalsystem, the liver receives a dual blood supply from the hepaticportal vein and hepatic arteries.
    • In the hepaticportalsystem, the liver receives a dual blood supply from the hepaticportal vein and hepatic arteries.
    • Oxygen is provided from both sources approximately half of the liver's oxygen demand is met by the hepaticportal vein, and half is met by the hepatic arteries.
    • The majority of capillaries in the body drain directly into the heart, making portalsystems unusual.
    • The hepaticportalsystem connects the capillaries of the gastrointestinal tract with the capillaries in the liver .

    Hepatic Portal Circulation

    • The hepaticportalsystem is responsible for directing blood from parts of the gastrointestinal tract to the liver.
    • The hepaticportalsystem is the system of veins comprising the hepaticportal vein and its tributaries.
    • The hepaticportal vein supplies about 75% of the blood the liver requires, with the other 25% supplied by the hepatic artery.
    • Blood from the hepatic artery is oxygenated but nutrient-poor compared to that supplied by the hepaticportal vein.
    • Since blood received from the hepaticportal vein may be contaminated with pathogens such as bacteria, the liver is rich in specialized immune cells called Kupffer cells that detect and destroy foreign organisms.

    Transport of Hormones

    • The endocrine system is a system of ductless glands that secrete hormones directly into the circulatory system to be carried long distances to other target organs that regulate key body and organ functions.
    • Some endocrine glands secrete into a portalsystem rather than the systemic circulation that allows for the direct targeting of hormones.
    • For example, hormones secreted by the pancreas pass into the hepaticportal vein that transports them directly to the liver.
    • Once within the circulatory system a small proportion of hormones circulate freely, however the majority are bound with a transport protein.
    • Describe the way in which hormones are transported in the endocrine system

    Veins

    • Although most veins take blood back to the heart, portal veins carry blood between capillary beds.
    • For example, the hepaticportal vein takes blood from the capillary beds in the digestive tract and transports it to the capillary beds in the liver.
    • Since this is an important function in mammals, damage to the hepaticportal vein can be dangerous.
    • Blood clotting in the hepaticportal vein can cause portal hypertension, which results in a decrease of blood fluid to the liver.
    • Systemic veins - Systemic veins drain the tissues of the body and deliver deoxygenated blood to the heart.

    Principal Veins

    • In the circulatory system, veins are blood vessels that carry blood towards the heart.
    • The above veins form part of the systemic circulatory system.
    • The renal and hepatic veins from the kidneys and liver respectively also feed into the inferior vena cava.
    • The hepaticportal vein carries blood from the gastrointestinal tract to the liver.
    • The portal vein is often described as a false vein because it conducts blood between capillary networks rather than between a capillary network and the heart.

    Associated Organs

    • The pancreas, liver, and gallbladder are the essential associated organs of the digestive system.
    • The liver is supplied by two main blood vessels on its right lobe: the hepatic artery and the portal vein.
    • The portal vein brings venous blood from the spleen, pancreas, and small intestine, so that the liver can process the nutrients and byproducts of food digestion.
    • The hepatic veins drain directly into the inferior vena cava.
    • These eventually drain into the right and left hepatic ducts, which in turn merge to form the common hepatic duct.

    Anatomy of the Liver and Gallbladder

    • It is connected to two large blood vessels, the hepatic artery and the portal vein.
    • The hepatic artery carries blood from the aorta to the liver, whereas the portal vein carries blood containing digested nutrients from the entire gastrointestinal tract and also from the spleen and pancreas to the liver.
    • Each lobule is made up of millions of hepatic cells which are the basic metabolic cells of the liver.
    • The neck tapers and connects to the biliary tree via the cystic duct, which then joins the common hepatic duct to become the common bile duct.

    Liver Function

    • The human liver is thought to be responsible for up to 500 separate functions, usually in combination with other systems and organs.
    • The liver is responsible for immunological effects, acting as a 'sieve' for antigens carried to it via the portalsystem.
    • This type of tissue is most common in alcoholic hepatitis (prevalence of 65%) and alcoholic cirrhosis (prevalence of 51%).

    The Portacaval Shunt

    • A connection is made between the portal vein, which supplies 75% of the liver's blood, and the inferior vena cava, the vein that drains blood from the lower two-thirds of the body.
    • The most common causes of liver disease resulting in portal hypertension are cirrhosis , caused by alcohol abuse, and viral hepatitis (hepatitis B and C).
    • Less common causes include diseases such as hemochromatosis, primary biliary cirrhosis (PBC), and portal vein thrombosis.

    Portals of Microbe Entry

    • In droplet contact and other airborne transmission it is generally the respiratory system through the nose, mouth, or eye surfaces.
    • Sexually transmitted diseases such as HIV and Hepatitis B are thought to be transmitted through unprotected sexual intercourse (including anal and oral routes), contaminated blood transfusions, sharing hypodermic needles, and from mother to child during pregnancy, delivery, or breastfeeding.
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