Liver
Overview
 
The liver is a vital organ present in vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

. The liver is necessary for survival; there is currently no way to compensate for the absence of liver function long term, although liver dialysis
Liver dialysis
Liver dialysis is a detoxification treatment for liver failure and has shown promise for patients with hepatorenal syndrome. It is similar to hemodialysis and based on the same principles...

 can be used short term.

This organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...

 plays a major role in metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 and has a number of functions in the body, including glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...

 storage, decomposition of red blood cells, plasma protein synthesis, hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

 production, and detoxification.
Unanswered Questions
Encyclopedia
The liver is a vital organ present in vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

. The liver is necessary for survival; there is currently no way to compensate for the absence of liver function long term, although liver dialysis
Liver dialysis
Liver dialysis is a detoxification treatment for liver failure and has shown promise for patients with hepatorenal syndrome. It is similar to hemodialysis and based on the same principles...

 can be used short term.

This organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...

 plays a major role in metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 and has a number of functions in the body, including glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...

 storage, decomposition of red blood cells, plasma protein synthesis, hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

 production, and detoxification. It lies below the diaphragm in the abdominal-pelvic region of the abdomen. It produces bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...

, an alkaline compound which aids in digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

 via the emulsification of lipids. The liver's highly specialized tissues
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

 regulate a wide variety of high-volume biochemical reactions, including the synthesis and breakdown of small and complex molecules, many of which are necessary for normal vital functions.

Medical terms related to the liver often start in hepato- or hepatic from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 word for liver, hēpar (ἡπαρ).

Anatomy

The liver is a reddish brown organ with four lobes of unequal size and shape. A human liver normally weighs 1.44–1.66 kg (3.2–3.7 lb), and is a soft, pinkish-brown, triangular organ. It is both the largest internal organ (the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

 being the largest organ overall) and the largest gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

 in the human body.
It is located in the right upper quadrant of the abdominal cavity
Abdominal cavity
The abdominal cavity is the body cavity of the human body that holds the bulk of the viscera. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm , and its oblique floor is the pelvic inlet...

, resting just below the diaphragm
Thoracic diaphragm
In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...

. The liver lies to the right of the stomach and overlies the gallbladder
Gallbladder
In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....

. It is connected to two large blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

s, one called the hepatic artery and one called the portal vein. The hepatic artery carries blood from the aorta, whereas the portal vein carries blood containing digested nutrients from the entire gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

 and also from the spleen and pancreas. These blood vessels subdivide into capillaries, which then lead to a lobule. Each lobule is made up of millions of hepatic cells which are the basic metabolic cells.

Blood flow

The liver gets a dual blood supply from the hepatic portal vein
Hepatic portal vein
The hepatic portal vein is not a true vein, because it does not conduct blood directly to the heart. It is a vessel in the abdominal cavity that drains blood from the gastrointestinal tract and spleen to capillary beds in the liver...

 and hepatic arteries. Supplying approximately 75% of the liver's blood supply, the hepatic portal vein carries venous blood
Venous blood
Venous blood is deoxygenated blood in the circulatory system. It runs in the systemic veins from the organs to the heart. Deoxygenated blood is then pumped by the heart to lungs via the pulmonary arteries, one of the few arteries in the body that carries deoxygenated blood .Venous blood is...

 drained from the spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

, gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

, and its associated organs. The hepatic arteries supply arterial blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 to the liver, accounting for the remainder of its blood flow
Blood flow
Blood flow is the continuous running of blood in the cardiovascular system.The human body is made up of several processes all carrying out various functions. We have the gastrointestinal system which aids the digestion and the absorption of food...

. Oxygen is provided from both sources; approximately half of the liver's oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries.
Blood flows through the liver sinusoids
Liver sinusoid
A liver sinusoid is a type of sinusoidal blood vessel that serves as a location for the oxygen-rich blood from the hepatic artery and the nutrient-rich blood from the portal vein....

 and empties into the central vein of each lobule. The central veins
Central veins of liver
The central vein of liver are veins found at the center of a "classic" hepatic lobule.They receive the blood mixed in the liver sinusoids and return it to circulation via the hepatic vein.-External links:* * *...

 coalesce into hepatic veins, which leave the liver.

Biliary flow

The term biliary tree
Biliary tree
The biliary tract is the common anatomical term for the path by which bile is secreted by the liver then transported to the first part of the small intestine, also known as the duodenum...

is derived from the arboreal branches of the bile ducts. The bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...

 produced in the liver is collected in bile canaliculi, which merge to form bile duct
Bile duct
A bile duct is any of a number of long tube-like structures that carry bile.Bile, required for the digestion of food, is excreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct to form the common bile duct, which opens into the intestine.The...

s. Within the liver, these ducts are called intrahepatic (within the liver) bile ducts, and once they exit the liver they are considered extrahepatic (outside the liver). The intrahepatic ducts eventually drain into the right and left hepatic ducts, which merge to form the common hepatic duct
Common hepatic duct
The common hepatic duct is the duct formed by the convergence of the right hepatic duct and the left hepatic duct . The common hepatic duct then joins the cystic duct coming from the gallbladder to form the common bile duct...

. The cystic duct
Cystic duct
The cystic duct is the short duct that joins the gall bladder to the common bile duct. It usually lies next to the cystic artery. It is of variable length...

 from the gallbladder
Gallbladder
In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....

 joins with the common hepatic duct
Common hepatic duct
The common hepatic duct is the duct formed by the convergence of the right hepatic duct and the left hepatic duct . The common hepatic duct then joins the cystic duct coming from the gallbladder to form the common bile duct...

 to form the common bile duct
Common bile duct
The common bile duct is a tube-like anatomic structure in the human gastrointestinal tract. It is formed by the union of the common hepatic duct and the cystic duct . It is later joined by the pancreatic duct to form the ampulla of Vater...

.

Bile can either drain directly into the duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...

 via the common bile duct, or be temporarily stored in the gallbladder
Gallbladder
In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....

 via the cystic duct. The common bile duct and the pancreatic duct
Pancreatic duct
The pancreatic duct, or duct of Wirsung , is a duct joining the pancreas to the common bile duct to supply pancreatic juices which aid in digestion provided by the "exocrine pancreas"...

 enter the second part of the duodenum together at the ampulla of Vater.

Peritoneal ligaments

Apart from a patch where it connects to the diaphragm (the so-called "bare area"), the liver is covered entirely by visceral peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...

, a thin, double-layered membrane
Mesothelium
The mesothelium is a membrane that forms the lining of several body cavities: the pleura , peritoneum and pericardium . Mesothelial tissue also surrounds the male internal reproductive organs and covers the internal reproductive organs of women...

 that reduces friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

 against other organs. The peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...

 folds back on itself to form the falciform ligament
Falciform ligament
The falciform ligament is a ligament that attaches the liver to the anterior body wall.It is a broad and thin antero-posterior peritoneal fold, falciform in shape, its base being directed downward and backward and its apex upward and backward...

 and the right
Right triangular ligament
The right triangular ligament is situated at the right extremity of the bare area, and is a small fold which passes to the diaphragm, being formed by the apposition of the upper and lower layers of the coronary ligament....

 and left triangular ligament
Left triangular ligament
The left triangular ligament is a fold of some considerable size, which connects the posterior part of the upper surface of the left lobe of the liver to the diaphragm; its anterior layer is continuous with the left layer of the falciform ligament....

s.

These "lits
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...

" are in no way related to the true anatomic ligaments
Ligament
In anatomy, the term ligament is used to denote any of three types of structures. Most commonly, it refers to fibrous tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.Ligament can also refer to:* Peritoneal...

 in joints, and have essentially no known functional importance, but they are easily recognizable surface landmarks. An exception to this is the falciform ligament, which attaches the liver to the posterior portion of the anterior body wall.

Lobes

Traditional gross anatomy
Gross anatomy
Gross anatomy is the study of anatomy at the macroscopic level. The term gross distinguishes it from other areas of anatomical study, including microscopic anatomy, which is studied on a microscopic scale, typically with a microscope....

 divided the liver into four lobe
Lobe (anatomy)
In anatomy, a lobe is a clear anatomical division or extension that can be determined without the use of a microscope This is in contrast to a lobule, which is a clear division only visible histologically....

s based on surface features.
The falciform ligament
Falciform ligament
The falciform ligament is a ligament that attaches the liver to the anterior body wall.It is a broad and thin antero-posterior peritoneal fold, falciform in shape, its base being directed downward and backward and its apex upward and backward...

 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 is 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 the quadrate lobe (the more inferior).

From behind, the lobes are divided up by the ligamentum venosum
Ligamentum venosum
The ligamentum venosum is the fibrous remnant of the ductus venosus of the fetal circulation. Usually, it is attached to the left branch of the portal vein within the porta hepatis...

 and ligamentum teres
Round ligament of liver
In anatomy, the round ligament of liver is a degenerative string of tissue that exists in the free edge of the falciform ligament of the liver...

 (anything left of these is the left lobe), the transverse fissure (or porta hepatis) divides the caudate
Caudate lobe of liver
The caudate lobe is situated upon the postero-superior surface of the liver on the right lobe of the liver, opposite the tenth and eleventh thoracic vertebrae...

 from the quadrate lobe, and the right sagittal fossa, which the inferior vena cava
Inferior vena cava
The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....

 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, 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.

Functional anatomy

Correspondence between anatomic lobes and Couinaud segments
Segment* Couinaud segments
Caudate 1
Lateral 2, 3
Medial 4a, 4b
Right 5, 6, 7, 8


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

4a. Superior subsegment of the medial segment

4b. 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



The central area where the common bile duct
Common bile duct
The common bile duct is a tube-like anatomic structure in the human gastrointestinal tract. It is formed by the union of the common hepatic duct and the cystic duct . It is later joined by the pancreatic duct to form the ampulla of Vater...

, hepatic portal vein
Hepatic portal vein
The hepatic portal vein is not a true vein, because it does not conduct blood directly to the heart. It is a vessel in the abdominal cavity that drains blood from the gastrointestinal tract and spleen to capillary beds in the liver...

, and hepatic artery proper
Hepatic artery proper
The hepatic artery proper , arises from the common hepatic artery and runs alongside the portal vein and the common bile duct to form the portal triad. The hepatic artery proper gives off a small supraduodenal artery to the duodenal bulb...

 enter is the hilum
Hilum (anatomy)
In human anatomy, the hilum is a depression or fissure where structures such as blood vessels and nerves enter an organ.-Examples of hila:* Hilum of kidney, admits the renal artery, vein, ureter, and nerves...

 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 an imaginary plane joining the gallbladder fossa to the inferior vena cava. The plane 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
Medial
- Medial magmas :In abstract algebra, a medial magma is a set with a binary operation which satisfies the identity \cdot = \cdot , or more simply, xy\cdot uv = xu\cdot yv...

 and lateral segments by the left hepatic vein. The fissure for the ligamentum teres
Round ligament of liver
In anatomy, the round ligament of liver is a degenerative string of tissue that exists in the free edge of the falciform ligament of the liver...

 also separates the medial and lateral segments. The medial segment is also called the quadrate lobe. In the widely used Couinaud
Claude Couinaud
Claude Couinaud was a French surgeon and anatomist who made significant contributions in the field of hepatobiliary surgery. He is best known for his detailed anatomic studies of the liver and was the first to describe its segmental anatomy...

 (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.

In other animals

The liver is found in all vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s, and is typically the largest visceral organ. Its form varies considerably in different species, and is largely determined by the shape and arrangement of the surrounding organs. Nonetheless, in most species it is divided into right and left lobes; exceptions to this general rule include snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...

s, where the shape of the body necessitates a simple cigar-like form. The internal structure of the liver is broadly similar in all vertebrates.

An organ sometimes referred to as a liver is found associated with the digestive tract of the primitive chordate Amphioxus. However, this is an enzyme secreting gland, not a metabolic organ, and it is unclear how truly homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...

 it is to the vertebrate liver.

Physiology

The various functions of the liver are carried out by the liver cells or hepatocyte
Hepatocyte
A hepatocyte is a cell of the main tissue of the liver. Hepatocytes make up 70-80% of the liver's cytoplasmic mass.These cells are involved in:* Protein synthesis* Protein storage* Transformation of carbohydrates...

s. Currently, there is no artificial organ
Artificial organ
An artificial organ is a man-made device that is implanted or integrated into a human to replace a natural organ, for the purpose of restoring a specific function or a group of related functions so the patient may return to as normal a life as possible...

 or device capable of emulating all the functions of the liver. Some functions can be emulated by liver dialysis
Liver dialysis
Liver dialysis is a detoxification treatment for liver failure and has shown promise for patients with hepatorenal syndrome. It is similar to hemodialysis and based on the same principles...

, an experimental treatment for liver failure
Liver failure
Acute liver failure is the appearance of severe complications rapidly after the first signs of liver disease , and indicates that the liver has sustained severe damage . The complications are hepatic encephalopathy and impaired protein synthesis...

. The liver is thought to be responsible for up to 500 separate functions, usually in combination with other systems and organs.

Synthesis

  • A large part of amino acid synthesis
    Amino acid synthesis
    For the non-biological synthesis of amino acids see: Strecker amino acid synthesisAmino acid synthesis is the set of biochemical processes by which the various amino acids are produced from other compounds. The substrates for these processes are various compounds in the organism's diet or growth...

  • The liver performs several roles in carbohydrate metabolism
    Carbohydrate metabolism
    Carbohydrate metabolism denotes the various biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates in living organisms....

    :
    • Gluconeogenesis
      Gluconeogenesis
      Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....

      (the synthesis of glucose
      Glucose
      Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

       from certain amino acid
      Amino acid
      Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

      s, lactate
      Lactic acid
      Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...

       or glycerol
      Glycerol
      Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...

      )
    • Glycogenolysis
      Glycogenolysis
      Glycogenolysis is the conversion of glycogen polymers to glucose monomers. Glycogen is catabolized by removal of a glucose monomer through cleavage with inorganic phosphate to produce glucose-1-phosphate...

      (the breakdown of glycogen
      Glycogen
      Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...

       into glucose
      Glucose
      Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

      )
    • Glycogenesis
      Glycogenesis
      Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen for storage. This process is activated during rest periods following the Cori cycle, in the liver, and also activated by insulin in response to high glucose levels, for example after a...

      (the formation of glycogen from glucose)(muscle tissues can also do this)
  • The liver is responsible for the mainstay of protein metabolism
    Metabolism
    Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

    , synthesis as well as degradation
  • The liver also performs several roles in lipid
    Lipid
    Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

     metabolism:
    • Cholesterol
      Cholesterol
      Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...

       synthesis
    • Lipogenesis
      Lipogenesis
      Lipogenesis is the process by which acetyl-CoA is converted to fats. The former is an intermediate stage in metabolism of simple sugars, such as glucose, a source of energy of living organisms. Through lipogenesis, the energy can be efficiently stored in the form of fats...

      , the production of triglyceride
      Triglyceride
      A triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....

      s (fats).
    • A bulk of the lipoproteins are synthesized in the liver.
  • The liver produces coagulation factors I
    Fibrinogen
    Fibrinogen is a soluble plasma glycoprotein, synthesised by the liver, that is converted by thrombin into fibrin during blood coagulation. This is achieved through processes in the coagulation cascade that activate the zymogen prothrombin to the serine protease thrombin, which is responsible for...

     (fibrinogen), II
    Thrombin
    Thrombin is a "trypsin-like" serine protease protein that in humans is encoded by the F2 gene. Prothrombin is proteolytically cleaved to form thrombin in the first step of the coagulation cascade, which ultimately results in the stemming of blood loss...

     (prothrombin), V
    Factor V
    Factor V is a protein of the coagulation system, rarely referred to as proaccelerin or labile factor. In contrast to most other coagulation factors, it is not enzymatically active but functions as a cofactor...

    , VII
    Factor VII
    Factor VII is one of the proteins that causes blood to clot in the coagulation cascade. It is an enzyme of the serine protease class. A recombinant form of human factor VIIa has U.S. Food and Drug Administration approval for uncontrolled bleeding in hemophilia patients...

    , IX
    Factor IX
    Factor IX is one of the serine proteases of the coagulation system; it belongs to peptidase family S1. Deficiency of this protein causes hemophilia B. It was discovered in 1952 after a young boy named Stephen Christmas was found to be lacking this exact factor, leading to...

    , X
    Factor X
    Factor X, also known by the eponym Stuart-Prower factor or as prothrombinase, is an enzyme of the coagulation cascade. It is a serine endopeptidase .-Physiology:...

     and XI
    Factor XI
    Factor XI or plasma thromboplastin antecedent is the zymogen form of factor XIa, one of the enzymes of the coagulation cascade. Like many other coagulation factors, it is a serine protease. In humans, Factor XI is encoded by the F11 gene....

    , as well as protein C
    Protein C
    Protein C, also known as autoprothrombin IIA and blood coagulation factor XIV, is a zymogenic protein, the activated form of which plays an important role in regulating blood clotting, inflammation, cell death and maintaining the permeability of blood vessel walls in humans and other animals...

    , protein S
    Protein S
    Protein S is a vitamin K-dependent plasma glycoprotein synthesized in the endothelium. In the circulation, Protein S exists in two forms: a free form and a complex form bound to complement protein C4b. In humans, protein S is encoded by the PROS1 gene...

     and antithrombin
    Antithrombin
    Antithrombin is a small protein molecule that inactivates several enzymes of the coagulation system. Antithrombin is a glycoprotein produced by the liver and consists of 432 amino acids. It contains three disulfide bonds and a total of four possible glycosylation sites...

    .
  • In the first trimester fetus
    Fetus
    A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

    , the liver is the main site of red blood cell
    Red blood cell
    Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...

     production. By the 32nd week of gestation
    Gestation
    Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....

    , the bone marrow
    Bone marrow
    Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

     has almost completely taken over that task.
  • The liver produces and excretes bile
    Bile
    Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...

     (a yellowish liquid) required for emulsifying fats. Some of the bile drains directly into the duodenum
    Duodenum
    The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...

    , and some is stored in the gallbladder
    Gallbladder
    In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....

    .
  • The liver also produces insulin-like growth factor 1
    Insulin-like growth factor 1
    Insulin-like growth factor 1 also known as somatomedin C is a protein that in humans is encoded by the IGF1 gene. IGF-1 has also been referred to as a "sulfation factor" and its effects were termed "nonsuppressible insulin-like activity" in the 1970s.IGF-1 is a hormone similar in molecular...

     (IGF-1), a polypeptide protein
    Protein
    Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

     hormone that plays an important role in childhood growth and continues to have anabolic effects
    Anabolism
    Anabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. One way of categorizing metabolic processes, whether at the cellular, organ or organism level is as 'anabolic' or as 'catabolic', which is the opposite...

     in adults.
  • The liver is a major site of thrombopoietin
    Thrombopoietin
    Thrombopoietin also known as megakaryocyte growth and development factor is a protein that in humans is encoded by the THPO gene....

     production. Thrombopoietin is a glycoprotein
    Glycoprotein
    Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...

     hormone that regulates the production of platelet
    Platelet
    Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes.  The average lifespan of a platelet is normally just 5 to 9 days...

    s by the bone marrow
    Bone marrow
    Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

    .

Breakdown

  • The breakdown of insulin
    Insulin
    Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

     and other hormone
    Hormone
    A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

    s
  • The liver glucoronidates
    Glucuronidation
    Glucuronidation is the addition of glucuronic acid to a substrate. Glucuronidation is often involved in xenobiotic metabolism of substances such as drugs, pollutants, bilirubin, androgens, estrogens, mineralocorticoids, glucocorticoids, fatty acid derivatives, retinoids, and bile acids...

     bilirubin
    Bilirubin
    Bilirubin is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases...

    , facilitating its excretion into bile
    Bile
    Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...

    .
  • The liver breaks down or modifies toxic substances (e.g., methylation) and most medicinal products in a process called drug metabolism
    Drug metabolism
    Drug metabolism is the biochemical modification of pharmaceutical substances by living organisms, usually through specialized enzymatic systems. This is a form of xenobiotic metabolism. Drug metabolism often converts lipophilic chemical compounds into more readily excreted polar products...

    . This sometimes results in toxication
    Toxication
    Toxication is the process of metabolism in which the metabolite of a compound is more toxic than the parent drug or chemical. A parent drug or chemical that was previously non-toxic may be called a protoxin.Toxication may involve:...

    , when the metabolite is more toxic than its precursor. Preferably, the toxins are conjugated to avail excretion in bile or urine.
  • The liver converts ammonia
    Ammonia
    Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

     to urea
    Urea
    Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....

     (urea cycle
    Urea cycle
    The urea cycle is a cycle of biochemical reactions occurring in many animals that produces urea from ammonia . This cycle was the first metabolic cycle discovered , five years before the discovery of the TCA cycle...

    )

Other functions

  • The liver stores a multitude of substances, including glucose (in the form of glycogen
    Glycogen
    Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...

    ), vitamin A
    Vitamin A
    Vitamin A is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is necessary for both low-light and color vision...

     (1–2 years' supply), vitamin D
    Vitamin D
    Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

     (1–4 months' supply), vitamin B12
    Vitamin B12
    Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...

     (1-3 years' supply), iron
    Iron
    Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

    , and copper
    Copper
    Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

    .
  • The liver is responsible for immunological effects- the reticuloendothelial system
    Reticuloendothelial system
    "Reticuloendothelial system" is an older term for the mononuclear phagocyte system. The mononuclear phagocyte system consists primarily of monocytes and macrophages. The spleen is the largest unit of the mononuclear phagocyte system. The monocyte is formed in the bone marrow and transported by the...

     of the liver contains many immunologically active cells, acting as a 'sieve' for antigens carried to it via the portal system.
  • The liver produces albumin
    Albumin
    Albumin refers generally to any protein that is water soluble, which is moderately soluble in concentrated salt solutions, and experiences heat denaturation. They are commonly found in blood plasma, and are unique to other blood proteins in that they are not glycosylated...

    , the major osmolar component of blood serum
    Blood plasma
    Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

    .
  • The liver synthesizes angiotensinogen, a hormone that is responsible for raising the blood pressure
    Blood pressure
    Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

     when activated by renin
    Renin
    Renin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...

    , an enzyme that is released when the kidney
    Juxtaglomerular apparatus
    The juxtaglomerular apparatus is a microscopic structure in the kidney, which regulates the function of each nephron. The juxtaglomerular apparatus is named for its proximity to the glomerulus: it is found between the vascular pole of the renal corpuscle and the returning distal convoluted tubule...

     senses low blood pressure
    Hypotension
    In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

    .

Diseases of the liver

The liver supports almost every organ in the body and is vital for survival. Because of its strategic location and multidimensional functions, the liver is also prone to many diseases.

The most common include: Infections such as hepatitis A
Hepatitis A
Hepatitis A is an acute infectious disease of the liver caused by the hepatitis A virus , an RNA virus, usually spread the fecal-oral route; transmitted person-to-person by ingestion of contaminated food or water or through direct contact with an infectious person...

, B, C, E, alcohol
Alcoholic beverage
An alcoholic beverage is a drink containing ethanol, commonly known as alcohol. Alcoholic beverages are divided into three general classes: beers, wines, and spirits. They are legally consumed in most countries, and over 100 countries have laws regulating their production, sale, and consumption...

 damage, fatty liver
Fatty liver
Fatty liver, also known as fatty liver disease , is a reversible condition where large vacuoles of triglyceride fat accumulate in liver cells via the process of steatosis...

, cirrhosis
Cirrhosis
Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules , leading to loss of liver function...

, cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

, drug damage (especially acetaminophen
Paracetamol
Paracetamol INN , or acetaminophen USAN , is a widely used over-the-counter analgesic and antipyretic . It is commonly used for the relief of headaches and other minor aches and pains and is a major ingredient in numerous cold and flu remedies...

 (also known as paracetamol) and cancer drugs)

Many diseases of the liver are accompanied by jaundice
Jaundice
Jaundice is a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae , and other mucous membranes caused by hyperbilirubinemia . This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid...

 caused by increased levels of bilirubin
Bilirubin
Bilirubin is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases...

 in the system. The bilirubin results from the breakup of the hemoglobin of dead red blood cell
Red blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...

s; normally, the liver removes bilirubin from the blood and excretes it through bile.

There are also many pediatric liver diseases including biliary atresia
Biliary atresia
Biliary atresia, also known as "extrahepatic ductopenia" and "progressive obliterative cholangiopathy" is a congenital or acquired disease of the liver and one of the principle forms of chronic rejection of a transplanted liver allograft. As a birth defect in newborn infants, it has an occurrence...

, alpha-1 antitrypsin deficiency, alagille syndrome
Alagille syndrome
Alagille syndrome is a genetic disorder that affects the liver, heart, kidney, and other systems of the body. Problems associated with the disorder generally become evident in infancy or early childhood...

, progressive familial intrahepatic cholestasis
Progressive familial intrahepatic cholestasis
Progressive familial intrahepatic cholestasis refers to a group of familial cholestatic conditions caused by defects in biliary epithelial transporters. The clinical presentation usually occurs first in childhood with progressive cholestasis...

, and Langerhans cell
Langerhans cell
Langerhans cells are dendritic cells of the skin and mucosa, and contain large granules called Birbeck granules. They are present in all layers of the epidermis, but are most prominant in the stratum spinosum. They also occur in the papillary dermis, particularly around blood vessels, as well as...

 histiocytosis, to name but a few.

Diseases that interfere with liver function will lead to derangement of these processes. However, the liver has a great capacity to regenerate
Regeneration (biology)
In biology, regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organs, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans. At its most...

 and has a large reserve capacity. In most cases, the liver only produces symptoms after extensive damage.

Liver diseases may be diagnosed by liver function tests
Liver function tests
Liver function tests , are groups of clinical biochemistry laboratory blood assays designed to give information about the state of a patient's liver. The parameters measured include PT/INR, aPTT, albumin, billirubin and others...

, for example, by production of acute phase protein
Acute phase protein
Acute-phase proteins are a class of proteins whose plasma concentrations increase or decrease in response to inflammation...

s.

Disease symptoms

The classic symptoms of liver damage include the following:
  • Pale stools occur when stercobilin
    Stercobilin
    Stercobilin is a tetrapyrrolic bile pigment and is one end-product of heme catabolism. It is the chemical responsible for the brown color of human fecal material and was originally isolated from feces in 1932...

    , a brown pigment, is absent from the stool. Stercobilin is derived from bilirubin metabolites produced in the liver.
  • Dark urine occurs when bilirubin mixes with urine
  • Jaundice (yellow skin and/or whites of the eyes) This is where bilirubin
    Bilirubin
    Bilirubin is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases...

     deposits in skin, causing an intense itch
    Itch
    Itch is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to classify it as any one type of sensory experience. Modern science has shown that itch has many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response...

    . Itching is the most common complaint by people who have liver failure. Often this itch cannot be relieved by drugs.
  • Swelling
    Swelling (medical)
    In medical parlance, swelling is the transient enlargement or protuberance in the body and may include tumors. According to cause, it may be congenital, traumatic, inflammatory, neoplastic or miscellaneous....

    of the abdomen, ankles and feet occurs because the liver fails to make albumin.
  • Excessive fatigue occurs from a generalized loss of nutrients, minerals
    Dietary mineral
    Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen present in common organic molecules. Examples of mineral elements include calcium, magnesium, potassium, sodium, zinc, and iodine...

     and vitamins.
  • Bruising
    Bruise
    A bruise, also called a contusion, is a type of relatively minor hematoma of tissue in which capillaries and sometimes venules are damaged by trauma, allowing blood to seep into the surrounding interstitial tissues. Bruises can involve capillaries at the level of skin, subcutaneous tissue, muscle,...

    and easy bleeding are other features of liver disease. The liver makes substances which help prevent bleeding. When liver damage occurs, these substances are no longer present and severe bleeding can occur.

Diagnosis

The diagnosis of liver function is made by blood tests
Blood test
A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a needle, or via fingerprick....

. Liver function tests can readily pinpoint the extent of liver damage. If infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 is suspected, then other serological
Serology
Serology is the scientific study of blood serum and other bodily fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum...

 tests are done. Sometimes, one may require an ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...

 or a CT scan to produce an image of the liver.

Physical examination of the liver is not accurate in determining the extent of liver damage. It can only reveal presence of tenderness or the size of liver, but in all cases, some type of radiological study is required to examine it.

Biopsy

The ideal way to determine damage to the liver is with a biopsy
Biopsy
A biopsy is a medical test involving sampling of cells or tissues for examination. It is the medical removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...

. A biopsy is not required in all cases, but may be necessary when the cause is unknown. A needle is inserted into the skin just below the rib cage and a biopsy is obtained. The tissue is sent to the laboratory, where it is analyzed under a microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

. Sometimes, a radiologist may assist the physician performing a liver biopsy
Liver biopsy
Liver biopsy is the biopsy from the liver. It is a medical test that is done to aid diagnosis of liver disease, to assess the severity of known liver disease, and to monitor the progress of treatment.-History:...

 by providing ultrasound guidance.

Regeneration

The liver is the only internal human organ capable of natural regeneration
Regeneration (biology)
In biology, regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organs, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans. At its most...

 of lost tissue
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

; as little as 25% of a liver can regenerate into a whole liver. This is, however, not true regeneration but rather compensatory growth. The lobes that are removed do not regrow and the growth of the liver is a restoration of function, not original form. This contrasts with true regeneration where both original function and form are restored.

This is predominantly due to the hepatocyte
Hepatocyte
A hepatocyte is a cell of the main tissue of the liver. Hepatocytes make up 70-80% of the liver's cytoplasmic mass.These cells are involved in:* Protein synthesis* Protein storage* Transformation of carbohydrates...

s re-entering the cell cycle
Cell cycle
The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...

. That is, the hepatocytes go from the quiescent G0 phase
G0 phase
The G0 phase is a period in the cell cycle in which cells exist in a quiescent state. G0 phase is viewed as either an extended G1 phase, where the cell is neither dividing nor preparing to divide, or a distinct quiescent stage that occurs outside of the cell cycle...

 to the G1 phase
G1 phase
The G1 phase is a period in the cell cycle during interphase, before the S phase. For many cells, this phase is the major period of cell growth during its lifespan. During this stage new organelles are being synthesized, so the cell requires both structural proteins and enzymes, resulting in great...

 and undergo mitosis. This process is activated by the p75 receptors. There is also some evidence of bipotential stem cell
Stem cell
This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...

s, called ovalocytes or hepatic oval cells, which are thought to reside in the canals of Hering
Canals of Hering
The Canals of Hering, or intrahepatic bile ductules, are part of the outflow system of exocrine bile product from the liver.-Anatomy:They are found between the bile canaliculi and interlobular bile ducts near the outer edge of a classic liver lobule...

. These cells can differentiate into either hepatocyte
Hepatocyte
A hepatocyte is a cell of the main tissue of the liver. Hepatocytes make up 70-80% of the liver's cytoplasmic mass.These cells are involved in:* Protein synthesis* Protein storage* Transformation of carbohydrates...

s or cholangiocytes, the latter being the cells that line the bile ducts.

Scientific and medical works about liver regeneration often refer to the Greek Titan
Titan (mythology)
In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age....

 Prometheus
Prometheus
In Greek mythology, Prometheus is a Titan, the son of Iapetus and Themis, and brother to Atlas, Epimetheus and Menoetius. He was a champion of mankind, known for his wily intelligence, who stole fire from Zeus and gave it to mortals...

 who was chained to a rock in the Caucasus where, each day, his liver was devoured by an eagle, only to grow back each night. Some think the myth indicates the ancient Greeks
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

 knew about the liver’s remarkable capacity for self-repair, though this claim has been challenged.

Liver transplantation

Human liver transplants were first performed by Thomas Starzl
Thomas Starzl
Thomas E. Starzl is an American physician, researcher, and is an expert on organ transplants. He performed the first human liver transplants, and has often been referred to as "the father of modern transplantation."-Life:...

 in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and Roy Calne
Roy Calne
Sir Roy Yorke Calne, FRS, is a British surgeon and pioneer in organ transplantation; he performed the first liver transplantation operation in Europe in 1968. His surgical procedures also laid claim to many other pioneering successes in his career: the world's first liver, heart, and lung...

 in Cambridge
Cambridge
The city of Cambridge is a university town and the administrative centre of the county of Cambridgeshire, England. It lies in East Anglia about north of London. Cambridge is at the heart of the high-technology centre known as Silicon Fen – a play on Silicon Valley and the fens surrounding the...

, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 in 1963 and 1965, respectively.
Liver transplantation
Liver transplantation
Liver transplantation or hepatic transplantation is the replacement of a diseased liver with a healthy liver allograft. The most commonly used technique is orthotopic transplantation, in which the native liver is removed and replaced by the donor organ in the same anatomic location as the original...

 is the only option for those with irreversible liver failure. Most transplants are done for chronic liver diseases leading to cirrhosis
Cirrhosis
Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules , leading to loss of liver function...

, such as chronic hepatitis C
Hepatitis C
Hepatitis C is an infectious disease primarily affecting the liver, caused by the hepatitis C virus . The infection is often asymptomatic, but chronic infection can lead to scarring of the liver and ultimately to cirrhosis, which is generally apparent after many years...

, alcoholism
Alcoholism
Alcoholism is a broad term for problems with alcohol, and is generally used to mean compulsive and uncontrolled consumption of alcoholic beverages, usually to the detriment of the drinker's health, personal relationships, and social standing...

, 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 donors who have died from fatal brain injury
Traumatic brain injury
Traumatic brain injury , also known as intracranial injury, occurs when an external force traumatically injures the brain. TBI can be classified based on severity, mechanism , or other features...

. 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 percent 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 percent of the liver. Due to the ability of the liver to regenerate
Regeneration (biology)
In biology, regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organs, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans. At its most...

, 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 two 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. The risk of postoperative complications (and death) is far greater in right-sided operations than that in left-sided operations.

With the recent advances of noninvasive imaging, living liver donors usually have to undergo imaging examinations for liver anatomy to decide if the anatomy is feasible for donation. The evaluation is usually performed by multidetector row computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...

 (MDCT) and magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

 (MRI). MDCT is good in vascular anatomy and volumetry. MRI is used for biliary tree anatomy. Donors with very unusual vascular anatomy, which makes them unsuitable for donation, could be screened out to avoid unnecessary operations.

Fetal blood supply

In the growing fetus, a major source of blood to the liver is the umbilical vein
Umbilical vein
The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta to the growing fetus.The blood pressure inside the umbilical vein is approximately 20 mmHg.-Development:...

 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
Falciform ligament
The falciform ligament is a ligament that attaches the liver to the anterior body wall.It is a broad and thin antero-posterior peritoneal fold, falciform in shape, its base being directed downward and backward and its apex upward and backward...

 of the liver to the inferior surface of the liver. There it joins with the left branch of the portal vein. The ductus venosus
Ductus venosus
In the fetus, the ductus venosus shunts approximately half of the blood flow of the umbilical vein directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver. In conjunction with the other fetal shunts, the foramen ovale and ductus arteriosus, it...

 carries blood from the left portal vein to the left hepatic vein and then to the inferior vena cava
Inferior vena cava
The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....

, 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
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

. The fetal liver releases some blood stem cells that migrate to the fetal thymus
Thymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....

, 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
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

.

After birth, the umbilical vein and ductus venosus are completely obliterated in two to five days; the former becomes the ligamentum teres
Round ligament of liver
In anatomy, the round ligament of liver is a degenerative string of tissue that exists in the free edge of the falciform ligament of the liver...

 and the latter becomes the ligamentum venosum
Ligamentum venosum
The ligamentum venosum is the fibrous remnant of the ductus venosus of the fetal circulation. Usually, it is attached to the left branch of the portal vein within the porta hepatis...

. In the disease state of cirrhosis
Cirrhosis
Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules , leading to loss of liver function...

 and portal hypertension
Portal hypertension
In medicine, portal hypertension is hypertension in the portal vein and its tributaries.It is often defined as a portal pressure gradient of 10 mmHg or greater.-Causes:Causes can be divided into prehepatic, intrahepatic, and posthepatic...

, the umbilical vein can open up again.

Cultural allusions

In Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

, Prometheus
Prometheus
In Greek mythology, Prometheus is a Titan, the son of Iapetus and Themis, and brother to Atlas, Epimetheus and Menoetius. He was a champion of mankind, known for his wily intelligence, who stole fire from Zeus and gave it to mortals...

 was punished by the gods for revealing fire to humans, by being chained to a rock where a vulture
Vulture
Vulture is the name given to two groups of convergently evolved scavenging birds, the New World Vultures including the well-known Californian and Andean Condors, and the Old World Vultures including the birds which are seen scavenging on carcasses of dead animals on African plains...

 (or an eagle
Eagle
Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...

) would peck out his liver, which would regenerate overnight. (The liver is the only human internal organ that actually can regenerate itself to a significant extent.) Many ancient peoples of the Near East and Mediterranean areas practiced a type of divination
Divination
Divination is the attempt to gain insight into a question or situation by way of an occultic standardized process or ritual...

 called haruspicy, where they tried to obtain information by examining the livers of sheep and other animals.

In Plato, and in later physiology, the liver was thought to be the seat of the darkest emotions (specifically wrath, jealousy and greed) which drive men to action. The Talmud
Talmud
The Talmud is a central text of mainstream Judaism. It takes the form of a record of rabbinic discussions pertaining to Jewish law, ethics, philosophy, customs and history....

 (tractate Berakhot 61b) refers to the liver as the seat of anger
Anger
Anger is an automatic response to ill treatment. It is the way a person indicates he or she will not tolerate certain types of behaviour. It is a feedback mechanism in which an unpleasant stimulus is met with an unpleasant response....

, with the gallbladder
Gallbladder
In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....

 counteracting this.

The Persian
Persian language
Persian is an Iranian language within the Indo-Iranian branch of the Indo-European languages. It is primarily spoken in Iran, Afghanistan, Tajikistan and countries which historically came under Persian influence...

, Urdu
Urdu
Urdu is a register of the Hindustani language that is identified with Muslims in South Asia. It belongs to the Indo-European family. Urdu is the national language and lingua franca of Pakistan. It is also widely spoken in some regions of India, where it is one of the 22 scheduled languages and an...

, and Hindi
Hindi
Standard Hindi, or more precisely Modern Standard Hindi, also known as Manak Hindi , High Hindi, Nagari Hindi, and Literary Hindi, is a standardized and sanskritized register of the Hindustani language derived from the Khariboli dialect of Delhi...

 languages (جگر or जिगर or jigar) refer to the liver in figurative speech to indicate courage and strong feelings, or "their best"; e.g., "This Mecca
Mecca
Mecca is a city in the Hijaz and the capital of Makkah province in Saudi Arabia. The city is located inland from Jeddah in a narrow valley at a height of above sea level...

 has thrown to you the pieces of its liver!". The term jan e jigar, literally "the strength (power) of my liver", is a term of endearment in Urdu. In Persian slang, jigar is used as an adjective for any object which is desirable, especially women. In the Zulu language
Zulu language
Zulu is the language of the Zulu people with about 10 million speakers, the vast majority of whom live in South Africa. Zulu is the most widely spoken home language in South Africa as well as being understood by over 50% of the population...

, the word for liver (isibindi) is the same as the word for courage.

The legend of Liver-Eating Johnson
Liver-Eating Johnson
John "Liver-Eating" Johnson was a mountain man of the American Old West.- Biography :Johnson is said to have been born near Little York, New Jersey, with the last name Garrison. Some accounts say that he joined the United States Navy in 1846...

 says that he would cut out and eat the liver of each man killed after dinner.

In the motion picture The Message
Mohammad, Messenger of God (film)
Mohammad, Messenger of God is a 1976 film directed by Moustapha Akkad chronicling the life and times of Muhammad, the prophet of Islam...

, Hind bint Utbah
Hind bint Utbah
Hind bint ‘Utbah was an Arab woman who lived in the late 6th and early 7th centuries CE; she was the wife of Abu Sufyan ibn Harb, a powerful man of Mecca, in western Arabia. Both Abu Sufyan and Hind originally opposed the Islamic prophet Muhammad...

 is implied or portrayed eating the liver of Hamza ibn ‘Abd al-Muttalib
Hamza ibn ‘Abd al-Muttalib
Hamza ibn ‘Abdul-Muttalib [b.568-d.625] was the paternal uncle of the Islamic prophet Muhammad, and his foster-brother. He and Muhammad were raised together as they were almost the same age. With excellence in the arts of wrestling and swordsmanship...

 during the Battle of Uhud
Battle of Uhud
The Battle of Uhud was fought on March 19, 625 at the valley located in front of Mount Uhud, in what is now northwestern Arabia. It occurred between a force from the Muslim community of Medina led by the Islamic prophet Muhammad, and a force led by Abu Sufyan ibn Harb from Mecca, the town from...

. Although there are narrations that suggest that Hind did "taste", rather than eat, the liver of Hamza, the authenticity of these narrations has to be questioned.

See also

  • Artificial liver
  • Bile
    Bile
    Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...

  • Bile canaliculus
    Bile canaliculus
    Bile canaliculus is a thin tube that collects bile secreted by hepatocytes. The bile canaliculi merge and form bile ductules, which eventually become common hepatic duct....

  • Hepatic cyst (liver cyst)
  • Hepatocyte
    Hepatocyte
    A hepatocyte is a cell of the main tissue of the liver. Hepatocytes make up 70-80% of the liver's cytoplasmic mass.These cells are involved in:* Protein synthesis* Protein storage* Transformation of carbohydrates...

  • Liver function tests
    Liver function tests
    Liver function tests , are groups of clinical biochemistry laboratory blood assays designed to give information about the state of a patient's liver. The parameters measured include PT/INR, aPTT, albumin, billirubin and others...

  • Liver shot (martial arts strike)
    Liver shot
    A liver shot is a punch, kick, or knee strike to the right side of the ribcage that damages the liver. Blunt force to the liver can be excruciatingly painful, and an especially effective shot will incapacitate a person...

  • Polycystic liver disease
    Polycystic liver disease
    Polycystic liver disease usually describes the presence of multiple cysts scattered throughout normal liver tissue, in association with polycystic kidney disease.-Pathophysiology:Associations with PRKCSH and SEC63 have been described....

  • Porto-Systemic anastomosis
    Anastomosis
    An anastomosis is the reconnection of two streams that previously branched out, such as blood vessels or leaf veins. The term is used in medicine, biology, mycology and geology....


External links

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