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Liver
Liver of a sheep: (1) right lobe, (2) left lobe, (3) caudate lobe, (4) quadrate lobe, (5) hepatic artery and portal vein, (6) hepatic lymph nodes, (7) gall bladder.
Position of the liver (red) in the abdomen.
Details
Precursorforegut
Arteryhepatic artery
Veinhepatic vein, portal vein
Nerveceliac ganglia, vagus[1]
Identifiers
MeSHD008099
TA98A05.8.01.001
TA23023
FMA7197
Anatomical terminology

The liver is an organ present in vertebrates and some other animals. It plays a major role in metabolism and has a number of functions in the body, including glycogen storage, plasma protein synthesis, and detoxification. This organ also is the largest gland in the human body. It lies below the diaphragm in the thoracic region of the abdomen.[2] It produces bile, an alkaline compound which aids in digestion. It also performs and regulates a wide variety of high-volume biochemical reactions requiring specialized tissues.

Medical terms related to the liver often start in hepato- or hepatic from the Greek word for liver, hēpar (ήπαρ[3]).


Anatomy

The adult human liver normally weighs between 1.7 - 3.0 kilograms (3.5 - 6.5 pounds), and it is a soft, pinkish-brown "boomerang shaped" organ. It is the second largest organ (the largest organ being the skin) and the largest gland within the human body.It is the heaviest organ in the body. It is located on the right side of the upper abdomen below the diaphragm. The liver lies on the right of the stomach and makes a kind of bed for the gallbladder (which stores bile).

Flow of blood

The splenic vein, joins the inferior mesenteric vein, which then together join with the superior mesenteric vein to form the portal vein, bringing venous blood from the spleen, pancreas, small intestine, and large intestine, so that the liver can process the nutrients and byproducts of food digestion.

The hepatic veins drain directly into the inferior vena cava.

The hepatic artery is generally a branch from the celiac trunk, although occasionally some or all of the blood can be from other branches such as the superior mesenteric artery.

Approximately 60% to 80% of the blood flow to the liver is from the portal venous system, and 1/4 is from the hepatic artery.

Flow of bile

The bile produced in the liver is collected in bile canaliculi, which merge to form bile ducts.

These eventually drain into the right and left hepatic ducts, which in turn merge to form the common hepatic duct. The cystic duct (from the gallbladder) joins with the common hepatic duct to form the common bile duct.

Bile can either drain directly into the duodenum via the common bile duct or be temporarily stored in the gallbladder via the cystic duct. The common bile duct and the pancreatic duct enter the duodenum together at the ampulla of Vater.

The branchings of the bile ducts resemble those of a tree, and indeed the term "biliary tree" is commonly used in this setting.

Regeneration

The liver is among the few internal human organs capable of natural regeneration of lost tissue; as little as 25% of remaining liver can regenerate into a whole liver again. App. 67% of a liver can grow back in one week.

This is predominantly due to the hepatocytes acting as unipotential stem cells (i.e. a single hepatocyte can divide into two hepatocyte daughter cells). There is also some evidence of bipotential stem cells, called oval cells, which can differentiate into either hepatocytes or cholangiocytes (cells that line the bile ducts).

Traditional (Surface) anatomy

Peritoneal ligaments

Apart from a patch where it connects to the diaphragm, the liver is covered entirely by visceral peritoneum, a thin, double-layered membrane that reduces friction against other organs. The peritoneum folds back on itself to form the falciform ligament and the right and left triangular ligaments.

These "ligaments" are in no way related to the true anatomic ligaments in joints, and have essentially no functional importance, but they are easily recognizable surface landmarks.

Lobes

Traditional gross anatomy divided the liver into four lobes based on surface features.

The falciform ligament is visible on the front (anterior side) of the liver. This divides the liver into a left anatomical lobe, and a right anatomical lobe.

If the liver flipped over, to look at it from behind (the visceral surface), there are two additional lobes between the right and left. These are the caudate lobe (the more superior), and below this the quadrate lobe.

From behind, the lobes are divided up by the ligamentum venosum and ligamentum teres (anything left of these is the left lobe), the transverse fissure (or porta hepatis) divides the caudate from the quadrate lobe, and the right sagittal fossa, which the inferior vena cava runs over, separates these two lobes from the right lobe.

Each of the lobes is made up of lobules, a vein goes from the centre of each lobule which then joins to the hepatic vein to carry blood out from the liver.

On the surface of the lobules there are ducts, veins and arteries that carry fluids to and from them.

Modern (Functional) anatomy

The central area where the common bile duct, portal vein, and hepatic artery enter the liver is the hilum or "porta hepatis". The duct, vein, and artery divide into left and right branches, and the portions of the liver supplied by these branches constitute the functional left and right lobes.

The functional lobes are separated by a plane joining the gallbladder fossa to the inferior vena cava. This separates the liver into the true right and left lobes. The middle hepatic vein also demarcates the true right and left lobes. The right lobe is further divided into an anterior and posterior segment by the right hepatic vein. The left lobe is divided into the medial and lateral segments by the left hepatic vein. The fissure for the ligamentum teres (the ligamentum teres becomes the falciform ligament) also separates the medial and lateral segmants. The medial segment is what used to be called the quadrate lobe. In the widely used Couinaud or "French" system, the functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein. The caudate lobe is a separate structure which receives blood flow from both the right- and left-sided vascular branches.[4][5] The subsegments corresponding to the anatomical lobes are as follows:

Segment* Couinaud segments
Caudate 1
Lateral 2, 3
Medial 4a, 4b
Right 5, 6, 7, 8
  • or lobe in the Caudate's case.

Each number in the list corresponds to one in the table.

  1. Caudate
  2. Superior subsegment of the lateral segment
  3. Inferior subsegment of the lateral segment
    1. Superior subsegment of the medial segment
    2. Inferior subsegment of the medial segment
  5. Inferior subsegment of the anterior segment
  6. Inferior subsegment of the posterior segment
  7. Superior subsegment of the posterior segment
  8. Superior subsegment of the anterior segment

Physiology

The various functions of the liver are carried out by the liver cells or hepatocytes.

Currently, there is no artificial organ or device capable of emulating all the functions of the liver. Some functions can be emulated by liver dialysis, an experimental treatment for liver failure.

Diseases of the liver

Many diseases of the liver are accompanied by jaundice caused by increased levels of bilirubin in the system. The bilirubin results from the breakup of the hemoglobin of dead red blood cells; normally, the liver removes bilirubin from the blood and excretes it through bile.

There are also many pediatric liver disease, including biliary atresia, alpha-1 antitrypsin deficiency, alagille syndrome, and progressive familial intrahepatic cholestasis, to name but a few.

A number of liver function tests are available to test the proper function of the liver. These test for the presence of enzymes in blood that are normally most abundant in liver tissue, metabolites or products.

Liver transplantation

Main article: Liver transplantation

Human liver transplant was first performed by Thomas Starzl in USA and Roy Calne in England in 1963 and 1965 respectively.

Liver transplantation is the only option for those with irreversible liver failure. Most transplants are done for chronic liver diseases leading to cirrhosis, such as chronic hepatitis C, alcoholism, autoimmune hepatitis, and many others. Less commonly, liver transplantation is done for fulminant hepatic failure, in which liver failure occurs over days to weeks.

Liver allografts for transplant usually come from non-living donors who have died from fatal brain injury. Living donor liver transplantation is a technique in which a portion of a living person's liver is removed and used to replace the entire liver of the recipient. This was first performed in 1989 for pediatric liver transplantation. Only 20% of an adult's liver (Couinaud segments 2 and 3) is needed to serve as a liver allograft for an infant or small child.

More recently, adult-to-adult liver transplantation has been done using the donor's right hepatic lobe which amounts to 60% of the liver. Due to the ability of the liver to regenerate, both the donor and recipient end up with normal liver function if all goes well. This procedure is more controversial as it entails performing a much larger operation on the donor, and indeed there have been at least 2 donor deaths out of the first several hundred cases. A recent publication has addressed the problem of donor mortality, and at least 14 cases have been found.[6] The risk of postoperative complications (and death) is far greater in right sided hepatectomy than left sided operations.

Development

The liver develops as an endodermal outpocketing of the foregut called the hepatic diverticulum. Its initial blood supply is primarily from the vitelline veins that drain blood from the yolk sac. The superior part of the hepatic diverticulum gives rise to the hepatocytes and bile ducts, while the inferior part becomes the gallbladder and its associated cystic duct.

Fetal blood supply

In the growing fetus, a major source of blood to the liver is the umbilical vein which supplies nutrients to the growing fetus. The umbilical vein enters the abdomen at the umbilicus, and passes upward along the free margin of the falciform ligament of the liver to the inferior surface of the liver. There it joins with the left branch of the portal vein. The ductus venosus carries blood from the left portal vein to the left hepatic vein and then to the inferior vena cava, allowing placental blood to bypass the liver.

In the fetus, the liver develops throughout normal gestation, and does not perform the normal filtration of the infant liver. The liver does not perform digestive processes because the fetus does not consume meals directly, but receives nourishment from the mother via the placenta. The fetal liver releases some blood stem cells that migrate to the fetal thymus, so initially the lymphocytes, called T-cells, are created from fetal liver stem cells. Once the fetus is delivered, the formation of blood stem cells in infants shifts to the red bone marrow.

After birth, the umbilical vein and ductus venosus are completely obliterated two to five days postpartum; the former becomes the ligamentum teres and the latter becomes the ligamentum venosum. In the disease state of cirrhosis and portal hypertension, the umbilical vein can open up again.

Liver as food

Pork liver
Nutritional value per 100 g (3.5 oz)
Energy561 kJ (134 kcal)
2.5 g
3.7 g
21 g
Vitamins and minerals
VitaminsQuantity
%DV†
Vitamin A equiv.
722%
6500 μg
Riboflavin (B2)
231%
3 mg
Niacin (B3)
94%
15 mg
Vitamin B6
41%
0.7 mg
Folate (B9)
53%
212 μg
Vitamin B12
1083%
26 μg
MineralsQuantity
%DV†
Iron
128%
23 mg
Sodium
4%
87 mg
Beef and chicken liver are comparable.
†Percentages estimated using US recommendations for adults,[7] except for potassium, which is estimated based on expert recommendation from the National Academies.[8]

Mammal and bird livers are commonly eaten as food: products include liver pâté, Leberwurst, Braunschweiger, foie gras, chopped liver, leverpostej and liver sashimi.

Both animal and fish livers are rich in iron and Vitamin A and cod liver oil is commonly used as a supplement. Very high doses of Vitamin A can be toxic; Antarctic explorers Douglas Mawson and Xavier Mertz were both poisoned, the latter fatally, from eating husky liver. In the US, the USDA specifies 3000 μg per day as a tolerable upper limit, which amounts to about 50 g of raw pork liver or, as reported in a non scientific source, 3 g of polar-bear liver.[9] However, acute vitamin A poisoning is not likely to result from liver consumption, since it is present in a less toxic form than in many dietary supplements.[10]

Cultural allusions

In Greek mythology, Prometheus was punished by the gods for revealing fire to humans by being chained to a rock where a vulture (or an eagle, Ethon) would peck out his liver, which would regenerate overnight. Curiously, the liver is the only human internal organ that actually can regenerate itself to a significant extent, a characteristic which may have already been known to the Greeks, possibly due to survived injuries in battle.

The Talmud (tractate Berakhot 61b) refers to the liver as the seat of anger, with the gallbladder counteracting this.

In Arabic and Persian language, the liver is used in figurative speech to refer to courage and strong feelings, or "their best," e.g. "This Mecca has thrown to you the pieces of its liver!" [11]

The legend of Liver-Eating Johnson says that he would cut out and eat the liver of each man killed.

In the motion picture The Message, Hind bint Utbah is implied or portrayed eating the liver of Hamza ibn ‘Abd al-Muttalib during the Battle of Uhud.

Inuit will not eat the liver of polar bears or seals [12]

In The Silence of the Lambs, Hannibal Lecter says famously, "I ate his liver with some fava beans and a nice amarone Chianti."

Further reading

The following are standard medical textbooks:
  • Eugene R. Schiff, Michael F. Sorrell, Willis C. Maddrey, eds. Schiff's diseases of the liver, 9th ed. Philadelphia : Lippincott, Williams & Wilkins, 2003. ISBN 0-7817-3007-4
  • Sheila Sherlock, James Dooley. Diseases of the liver and biliary system, 11th ed. Oxford, UK ; Malden, MA : Blackwell Science. 2002. ISBN 0-632-05582-0
  • David Zakim, Thomas D. Boyer. eds. Hepatology: a textbook of liver disease, 4th ed. Philadelphia: Saunders. 2003. ISBN 0-7216-9051-3
These are for the lay reader or patient:
  • Sanjiv Chopra. The Liver Book: A Comprehensive Guide to Diagnosis, Treatment, and Recovery, Atria, 2002, ISBN 0-7434-0585-4
  • Melissa Palmer. Dr. Melissa Palmer's Guide to Hepatitis and Liver Disease: What You Need to Know, Avery Publishing Group; Revised edition May 24, 2004, ISBN 1-58333-188-3. her webpage.
  • Howard J. Worman. The Liver Disorders Sourcebook, McGraw-Hill, 1999, ISBN 0-7373-0090-6. his Columbia University web site, "Diseases of the liver"

See also

Look up liver in Wiktionary, the free dictionary.

References

  1. ^ Template:GeorgiaPhysiology
  2. ^ KMLE Medical Dictionary. "KMLE Medical Dictionary Definition of liver". {{cite web}}: External link in |author= (help) Retrieved 2007-02-16
  3. ^ The Greek word "ήπαρ" was derived from hēpaomai (ηπάομαι): to mend, to repair, hence hēpar actually means "repairable", indicating that this organ can regenerate itself spontaneously in the case of lesion.
  4. ^ http://dpi.radiology.uiowa.edu/nlm/app/livertoc/liver/liver.html
  5. ^ http://www.uni-bonn.de/~umm705/quiz0403.htm
  6. ^ Bramstedt K (2006). "Living liver donor mortality: where do we stand?". Am J Gastroenterol. 101 (4): 755–9. PMID 16494593.
  7. ^ United States Food and Drug Administration (2024). "Daily Value on the Nutrition and Supplement Facts Labels". FDA. Archived from the original on 2024-03-27. Retrieved 2024-03-28.
  8. ^ National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Food and Nutrition Board; Committee to Review the Dietary Reference Intakes for Sodium and Potassium (2019). Oria, Maria; Harrison, Meghan; Stallings, Virginia A. (eds.). Dietary Reference Intakes for Sodium and Potassium. The National Academies Collection: Reports funded by National Institutes of Health. Washington, DC: National Academies Press (US). ISBN 978-0-309-48834-1. PMID 30844154. Archived from the original on 2024-05-09. Retrieved 2024-06-21.
  9. ^ A. Aggrawal, Death by Vitamin A
  10. ^ Myhre et al., "Water-miscible, emulsified, and solid forms of retinol supplements are more toxic than oil-based preparations", Am. J. Clinical Nutrition, 78, 1152 (2003)
  11. ^ http://www.shawuniversitymosque.org/m/faq_qanda.php?id=94
  12. ^ http://www.studentbmj.com/issues/02/05/life/158.php

Additional images

  • Accessory digestive system.
    Accessory digestive system.
  • Digestive organs.
    Digestive organs.
  • The liver and the veins in connection with it, of a human embryo, twenty-four or twenty-five days old, as seen from the ventral surface.
    The liver and the veins in connection with it, of a human embryo, twenty-four or twenty-five days old, as seen from the ventral surface.
  • Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas.
    Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas.
  • Front of abdomen, showing surface markings for liver, stomach, and great intestine
    Front of abdomen, showing surface markings for liver, stomach, and great intestine
  • Topography of thoracic and abdominal viscera.
    Topography of thoracic and abdominal viscera.
  • Portal triad
    Portal triad
  • Frontal view from Gray's Anatomy(1918)
    Frontal view from Gray's Anatomy(1918)
  • Back view from Gray's Anatomy(1918)
    Back view from Gray's Anatomy(1918)
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