The liver is a major organ only found in vertebrates which performs many essential biological functions such as

detoxification Detoxification or detoxication (detox for short) is the physiological or medicinal removal of toxic substances from a living organism, including the human body, which is mainly carried out by the liver. Additionally, it can refer to the period of ...

of the organism, and the synthesis of proteins and biochemicals necessary for

digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...

and growth. In humans, it is located in the

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

of the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

, below the diaphragm. Its other roles in

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

include the regulation of glycogen storage, decomposition of

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

s, and the production of

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

s. The liver is an

accessory digestive organ The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...

that produces

bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile ...

, an

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

fluid containing

cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...

and

bile acid Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Primary b ...

s, which helps the breakdown of fat. The

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

, a small pouch that sits just under the liver, stores bile produced by the liver which is later moved to the small intestine to complete digestion. The liver's highly specialized tissue, consisting mostly of

hepatocyte A hepatocyte is a cell of the main parenchymal tissue of the liver. Hepatocytes make up 80% of the liver's mass. These cells are involved in: * Protein synthesis * Protein storage * Transformation of carbohydrates * Synthesis of cholesterol, ...

s, regulates 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. Estimates regarding the organ's total number of functions vary, but is generally cited as being around 500. It is not known how to compensate for the absence of liver function in the long term, although

liver dialysis A liver support system or diachysis is a type of therapeutic device to assist in performing the functions of the liver. Such systems focus either on removing the accumulating toxins (liver dialysis), or providing additional replacement of the met ...

techniques can be used in the short term. Artificial livers have not been developed to promote long-term replacement in the absence of the liver. ,

liver transplantation Liver transplantation or hepatic transplantation is the replacement of a diseased liver with the healthy liver from another person (allograft). Liver transplantation is a treatment option for end-stage liver disease and acute liver failure, al ...

is the only option for complete liver failure.

Structure

The liver is a reddish-brown, wedge-shaped organ with two lobes of unequal size and shape. A human liver normally weighs approximately and has a width of about . There is considerable size variation between individuals, with the standard

reference range In medicine and health-related fields, a reference range or reference interval is the range or the interval of values that is deemed normal for a physiological measurement in healthy persons (for example, the amount of creatinine in the blood, or ...

for men being and for women . It is both the heaviest internal organ and the largest

gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland). Structure De ...

in the human body. Located in the right upper quadrant of the

abdominal cavity The abdominal cavity is a large body cavity in humans and many other animals that contains many organs. It is a part of the abdominopelvic cavity. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the th ...

, it rests just below the diaphragm, to the right of the stomach, and overlies the

. The liver is connected to two large

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

s: the

hepatic artery The common hepatic artery is a short blood vessel that supplies oxygenated blood to the liver, pylorus of the stomach, duodenum, pancreas, and gallbladder. It arises from the celiac artery and has the following branches: Additional images ...

and the

portal vein The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Approxima ...

. The hepatic artery carries oxygen-rich blood from the aorta via the

celiac trunk The celiac () artery (also spelled ''coeliac''), also known as the celiac trunk or truncus coeliacus, is the first major branch of the abdominal aorta. It is about 1.25 cm in length. Branching from the aorta at thoracic vertebra 12 (T12) i ...

, whereas the portal vein carries blood rich in digested nutrients from the entire

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

and also from the

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

and

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

. These blood vessels subdivide into small capillaries known as

liver sinusoid A liver sinusoid is a type of capillary known as a sinusoidal capillary, discontinuous capillary or sinusoid, that is similar to a fenestrated capillary, having discontinuous endothelium that serves as a location for mixing of the oxygen-rich blo ...

s, which then lead to

lobules In anatomy, a lobe is a clear anatomical division or extension of an organ (as seen for example in the brain, lung, liver, or kidney) that can be determined without the use of a microscope at the gross anatomy level. This is in contrast to the mu ...

. Lobules are the functional units of the liver. Each lobule is made up of millions of

hepatic cells Hepatic stellate cells (HSC), also known as perisinusoidal cells or Ito cells (earlier ''lipocytes'' or ''fat-storing cells''), are pericytes found in the perisinusoidal space of the liver, also known as the space of Disse (a small area between th ...

(hepatocytes), which are the basic metabolic cells. The lobules are held together by a fine, dense, irregular
fibroelastic
connective tissue layer extending from the fibrous capsule covering the entire liver known as

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

. This extends into the structure of the liver by accompanying the blood vessels, ducts, and nerves at the hepatic hilum. The whole surface of the liver, except for the

bare area The bare area of the liver (nonperitoneal area) is a large triangular area on the thoracic diaphragm, diaphragmatic surface of the liver. It is the only part of the liver with no peritoneal covering, although it is still covered by Glisson’s ca ...

, is covered in a

serous In physiology, serous fluid or serosal fluid (originating from the Medieval Latin word ''serosus'', from Latin ''serum'') is any of various body fluids resembling serum, that are typically pale yellow or transparent and of a benign nature. The fl ...

coat derived from the

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesoth ...

, and this firmly adheres to the inner

Gross anatomy

Terminology related to the liver often starts in ''hepat-'' from ἡπατο-, from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

word for liver.

Lobes

The liver is grossly divided into two parts when viewed from above – a right and a left lobe - and four parts when viewed from below (left, right, caudate, and

quadrate lobe In human anatomy, the liver is divided grossly into four parts or lobes: the right lobe, the left lobe, the caudate lobe, and the quadrate lobe. Seen from the front – the diaphragmatic surface - the liver is divided into two lobes: the right ...

s). The

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

makes a superficial division of the liver into a left and right lobe. From below, the two additional lobes are located between the right and left lobes, one in front of the other. A line can be imagined running from the left of the

vena cava In anatomy, the venae cavae (; singular: vena cava ; ) are two large veins (great vessels) that return deoxygenated blood from the body into the heart. In humans they are the superior vena cava and the inferior vena cava, and both empty into the ...

and all the way forward to divide the liver and gallbladder into two halves. This line is called

Cantlie's line In human anatomy, the Cantlie line or Cantlie's line is an imaginary division of the liver. The division divides the liver into two planes, extending from the middle hepatic vein to the middle of the gallbladder. It is useful for performing hep ...

. Other anatomical landmarks include the

ligamentum venosum The ligamentum venosum, also known as Arantius' ligament, 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. It may be continuous with the r ...

and the

round ligament of the liver The round ligament of the liver (or ligamentum teres, or ligamentum teres hepatis) is a ligament that forms part of the free edge of the falciform ligament of the liver. It connects the liver to the Navel, umbilicus. It is the remnant of the left ...

, which further divide the left side of the liver in two sections. An important anatomical landmark, the

porta hepatis The porta hepatis or transverse fissure of the liver is a short but deep fissure, about 5 cm long, extending transversely beneath the left portion of the right lobe of the liver, nearer its posterior surface than its anterior border. It join ...

, divides this left portion into four segments, which can be numbered starting at the caudate lobe as I in an anticlockwise manner. From this parietal view, seven segments can be seen, because the eighth segment is only visible in the

visceral In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...

view.

Surfaces

On the diaphragmatic surface, apart from a triangular bare area where it connects to the diaphragm, the liver is covered by a thin, double-layered membrane, the

, that helps to reduce friction against other organs. This surface covers the convex shape of the two lobes where it accommodates the shape of the diaphragm. The peritoneum folds back on itself to form the

and the

right Rights are law, legal, social, or ethics, ethical principles of Liberty, freedom or entitlement; that is, rights are the fundamental normative rules about what is allowed of people or owed to people according to some legal system, social convent ...

and

left triangular ligament The left triangular ligament is a large peritoneal fold. It connects the posterior part of the upper surface of the left lobe of the liver to the thoracic diaphragm. Structure The left triangular ligament connects the posterior part of the upp ...

s. These

peritoneal ligament Peritoneal ligaments are folds of peritoneum that are used to connect viscera to viscera or the abdominal wall. There are multiple named ligaments that usually are named in accordance with what they are. * Gastrocolic ligament, connects the stomac ...

s are not related to the anatomic ligaments in joints, and the right and left triangular ligaments have no known functional importance, though they serve as surface landmarks. The falciform ligament functions to attach the liver to the posterior portion of the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

body wall. The visceral surface or inferior surface is uneven and concave. It is covered in peritoneum apart from where it attaches the gallbladder and the porta hepatis. The fossa of gallbladder lies to the right of the quadrate lobe, occupied by the gallbladder with its cystic duct close to the right end of porta hepatis.

Impressions

Several impressions on the surface of the liver accommodate the various adjacent structures and organs. Underneath the right lobe and to the right of the gallbladder fossa are two impressions, one behind the other and separated by a ridge. The one in front is a shallow colic impression, formed by the

hepatic flexure In the anatomy of the human digestive tract, there are two colic flexures, or curvatures in the transverse colon. The right colic flexure is also known as the hepatic flexure, and the left colic flexure is also known as the splenic flexure. Note ...

and the one behind is a deeper renal impression accommodating part of the right kidney and part of the suprarenal gland. The suprarenal impression is a small, triangular, depressed area on the liver. It is located close to the right of the fossa, between the bare area and the caudate lobe, and immediately above the renal impression. The greater part of the suprarenal impression is devoid of peritoneum and it lodges the right suprarenal gland. Medial to the renal impression is a third and slightly marked impression, lying between it and the neck of the gall bladder. This is caused by the descending portion of the duodenum, and is known as the duodenal impression. The inferior surface of the left lobe of the liver presents behind and to the left of the gastric impression. This is moulded over the upper front surface of the stomach, and to the right of this is a rounded eminence, the

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

, which fits into the concavity of the lesser curvature of the stomach and lies in front of the anterior layer of the

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

Microscopic anatomy

Microscopically, each liver lobe is seen to be made up of

hepatic lobule In histology (microscopic anatomy), the lobules of liver, or hepatic lobules, are small divisions of the liver defined at the microscopic scale. The hepatic lobule is a building block of the liver tissue, consisting of a portal triad, hepatocyte ...

s. The lobules are roughly hexagonal, and consist of plates of hepatocytes, and sinusoids radiating from a central vein towards an imaginary perimeter of interlobular portal triads. The central vein joins to the hepatic vein to carry blood out from the liver. A distinctive component of a lobule is the

portal triad In histology (microscopic anatomy), the lobules of liver, or hepatic lobules, are small divisions of the liver defined at the microscopic scale. The hepatic lobule is a building block of the liver tissue, consisting of a portal triad, hepatocyte ...

, which can be found running along each of the lobule's corners. The portal triad consists of the hepatic artery, the portal vein, and the common bile duct. The triad may be seen on a liver ultrasound, as a

Mickey Mouse sign Mickey Mouse sign is a medical sign resembling the head of Mickey Mouse, the Walt Disney character. Presented for the very first time at the CHIVA's Meeting, Berlin 2002 by Dr. Lurdes Cerol, this sign has been described as the image at the groin whe ...

with the portal vein as the head, and the hepatic artery, and the common bile duct as the ears.

Histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...

, the study of microscopic anatomy, shows two major types of liver cell: parenchymal cells and nonparenchymal cells. About 70–85% of the liver volume is occupied by parenchymal hepatocytes. Nonparenchymal cells constitute 40% of the total number of liver cells but only 6.5% of its volume. The

s are lined with two types of cell,

sinusoidal endothelial cells A liver sinusoid is a type of capillary known as a sinusoidal capillary, discontinuous capillary or sinusoid, that is similar to a fenestrated capillary, having discontinuous endothelium that serves as a location for mixing of the oxygen-rich blo ...

, and

phagocytic Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...

Kupffer cells Kupffer cells, also known as stellate macrophages and Kupffer–Browicz cells, are specialized cells localized in the liver within the lumen of the liver sinusoids and are adhesive to their endothelial cells which make up the blood vessel walls. Ku ...

Hepatic stellate cell Hepatic stellate cells (HSC), also known as perisinusoidal cells or Ito cells (earlier ''lipocytes'' or ''fat-storing cells''), are pericytes found in the perisinusoidal space of the liver, also known as the space of Disse (a small area between th ...

s are nonparenchymal cells found in the

perisinusoidal space The perisinusoidal space (or space of Disse) is a location in the liver between a hepatocyte and a sinusoid. It contains the blood plasma. Microvilli of hepatocytes extend into this space, allowing proteins and other plasma components from the ...

, between a sinusoid and a hepatocyte. Additionally, intrahepatic

lymphocytes A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adap ...

are often present in the sinusoidal lumen. 2423 Microscopic Anatomy of Liver.jpg, Microscopic anatomy of the liver 2104 Three Major Capillary Types.jpg, Types of capillaries–sinusoid on right 3D Medical Animation liver parts.jpg, alt=3D Medical Animation Still Shot Depicting parts of liver, 3D Medical Animation Still Shot Depicting parts of liver

Functional anatomy

The central area or hepatic hilum, includes the opening known as the porta hepatis which carries the

common bile duct The common bile duct, sometimes abbreviated as CBD, is a duct in the gastrointestinal tract of organisms that have a gallbladder. It is formed by the confluence of the common hepatic duct and cystic duct and terminates by uniting with pancreati ...

and

common hepatic artery The common hepatic artery is a short blood vessel that supplies oxygenated blood to the liver, pylorus of the stomach, duodenum, pancreas, and gallbladder. It arises from the celiac artery and has the following branches: Additional images ...

, and the opening for the portal vein. The duct, vein, and artery divide into left and right branches, and the areas of the liver supplied by these branches constitute the functional left and right lobes. The functional lobes are separated by the imaginary plane, Cantlie's line, 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

and posterior segment by the right hepatic vein. The left lobe is divided into the medial and

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...

segments by the left hepatic vein. The hilum of the liver is described in terms of three ''plates'' that contain the

bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. It ...

s and blood vessels. The contents of the whole plate system are surrounded by a sheath. The three plates are the ''hilar plate'', the ''cystic plate'' and the ''umbilical plate'' and the plate system is the site of the many anatomical variations to be found in the liver.

Couinaud classification system

Liver 04 Couinaud classification animation

In the widely used

Couinaud Claude Couinaud (12 February 1922, in Neuilly-sur-Seine – 4 May 2008, in Paris) was a French surgeon and anatomist who made significant contributions in the field of hepatobiliary The biliary tract, (biliary tree or biliary system) refers ...

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 that receives blood flow from both the right- and left-sided vascular branches. The Couinaud classification divides the liver into eight functionally independent

liver segment A liver segment is one of eight segments of the liver as described in the widely used Couinaud classification (named after Claude Couinaud) in the anatomy of the liver. This system divides the lobes of the liver into eight segments based on a t ...

s. Each segment has its own vascular inflow, outflow and biliary drainage. In the centre of each segment are branches of the portal vein, hepatic artery, and bile duct. In the periphery of each segment is vascular outflow through the hepatic veins. The classification system uses the vascular supply in the liver to separate the functional units (numbered I to VIII) with unit 1, the caudate lobe, receiving its supply from both the right and the left branches of the portal vein. It contains one or more hepatic veins which drain directly into the

inferior vena cava The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...

. The remainder of the units (II to VIII) are numbered in a clockwise fashion:

Gene and protein expression

About 20,000 protein coding genes are expressed in human cells and 60% of these genes are expressed in a normal, adult liver. Over 400 genes are more specifically expressed in the liver, with some 150 genes highly specific for liver tissue. A large fraction of the corresponding liver-specific proteins are mainly expressed in hepatocytes and secreted into the blood and constitute plasma proteins and

hepatokines Hepatokines (Greek ''heapto-'', liver; and ''-kinos'', movement) are proteins produced by liver cells (hepatocytes) that are secreted into the circulation and function as hormones across the organism. Research is mostly focused on hepatokines that ...

. Other liver-specific proteins are certain

liver enzymes Liver function tests (LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial thromboplastin ti ...

such as HAO1 and

RDH16 Retinol dehydrogenase 16 (all-trans) is a protein that in humans is encoded by the ''RDH16'' gene. The gene is also known as ''RODH-4'' and ''SDR9C8''. Model organisms Model organisms have been used in the study of RDH16 function. A conditiona ...

, proteins involved in bile synthesis such as

BAAT Bile acid-CoA:amino acid N-acyltransferase is an enzyme that in humans is encoded by the ''BAAT'' gene. The protein encoded by this gene is a liver enzyme that catalyzes the transfer of the bile acid moiety from the acyl-CoA thioester to either g ...

and SLC27A5, and transporter proteins involved in the metabolism of drugs, such as ABCB11 and SLC2A2. Examples of highly liver-specific proteins include apolipoprotein A II, coagulation factors F2 and F9, complement factor related proteins, and the

fibrinogen beta chain Fibrinogen beta chain, also known as FGB, is a gene found in humans and most other vertebrates with a similar system of blood coagulation. The protein encoded by this gene is the beta component of fibrinogen, a blood-borne glycoprotein composed o ...

protein.

Development

Organogenesis Organogenesis is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the internal orga ...

, the development of the organs, takes place from the third to the eighth week during

embryogenesis An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

. The origins of the liver lie in both the ventral portion of the

foregut The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct. Beyond the stomach, the foregut is attached to the abdominal walls by mesentery. The foregut arises from the endoderm, deve ...

endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...

(endoderm being one of the three embryonic

germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce two or three pr ...

s) and the constituents of the adjacent

septum transversum The septum transversum is a thick mass of cranial mesenchyme, formed in the embryo, that gives rise to parts of the thoracic diaphragm and the ventral mesentery of the foregut in the developed human being and other mammals. Origins The septum t ...

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every o ...

. In the human

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

, the hepatic diverticulum is the tube of endoderm that extends out from the foregut into the surrounding mesenchyme. The mesenchyme of septum transversum induces this endoderm to proliferate, to branch, and to form the glandular epithelium of the liver. A portion of the hepatic diverticulum (that region closest to the digestive tube) continues to function as the drainage duct of the liver, and a branch from this duct produces the gallbladder. Besides signals from the septum transversum mesenchyme,

fibroblast growth factor Fibroblast growth factors (FGF) are a family of cell signalling proteins produced by macrophages; they are involved in a wide variety of processes, most notably as crucial elements for normal development in animal cells. Any irregularities in the ...

from the developing heart also contributes to hepatic competence, along with

retinoic acid Retinoic acid (used simplified here for all-''trans''-retinoic acid) is a metabolite of vitamin A1 (all-''trans''-retinol) that mediates the functions of vitamin A1 required for growth and development. All-''trans''-retinoic acid is required in ...

emanating from the

lateral plate mesoderm The lateral plate mesoderm is the mesoderm that is found at the periphery of the embryo. It is to the side of the paraxial mesoderm, and further to the axial mesoderm. The lateral plate mesoderm is separated from the paraxial mesoderm by a narrow ...

. The hepatic endodermal cells undergo a morphological transition from columnar to pseudostratified resulting in thickening into the early liver bud. Their expansion forms a population of the bipotential hepatoblasts. Hepatic stellate cells are derived from mesenchyme. After migration of hepatoblasts into the septum transversum mesenchyme, the hepatic architecture begins to be established, with liver sinusoids and bile canaliculi appearing. The liver bud separates into the lobes. The left

umbilical vein The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta into the growing fetus. The umbilical vein provides convenient access to the central circulation of a neonate for restoration of blood vo ...

becomes the

ductus venosus In the fetus, the ''ductus venosus'' (Arantius' duct after Julius Caesar Aranzi) shunts a portion of umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver. Compared to ...

and the right

vitelline vein The vitelline veins are veins that drain blood from the yolk sac and the gut tube during gestation. Path They run upward at first in front, and subsequently on either side of the intestinal canal. They unite on the ventral aspect of the canal. ...

becomes the portal vein. The expanding liver bud is colonized by

hematopoietic cells Haematopoiesis (, from Greek , 'blood' and 'to make'; also hematopoiesis in American English; sometimes also h(a)emopoiesis) is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells. ...

. The bipotential hepatoblasts begin differentiating into biliary epithelial cells and hepatocytes. The biliary epithelial cells differentiate from hepatoblasts around portal veins, first producing a monolayer, and then a bilayer of cuboidal cells. In ductal plate, focal dilations emerge at points in the bilayer, become surrounded by portal mesenchyme, and undergo tubulogenesis into intrahepatic bile ducts. Hepatoblasts not adjacent to portal veins instead differentiate into hepatocytes and arrange into cords lined by sinusoidal epithelial cells and bile canaliculi. Once hepatoblasts are specified into hepatocytes and undergo further expansion, they begin acquiring the functions of a mature hepatocyte, and eventually mature hepatocytes appear as highly polarized epithelial cells with abundant glycogen accumulation. In the adult liver, hepatocytes are not equivalent, with position along the portocentrovenular axis within a liver lobule dictating expression of metabolic genes involved in drug metabolism, carbohydrate metabolism, ammonia detoxification, and bile production and secretion. WNT/β-catenin has now been identified to be playing a key role in this phenomenon. Ultrasound liver right lobe and right kidney

Ultrasound liver right lobe and right kidney

At birth, the liver comprises roughly 4% of body weight and weighs on average about . Over the course of further development, it will increase to but will only take up 2.5–3.5% of body weight.

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

, allowing placental blood to bypass the liver. In the fetus, the liver does not perform the normal digestive processes and filtration of the infant liver because nutrients are received directly from the mother via the

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...

. The fetal liver releases some blood stem cells that migrate to the fetal

thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...

, creating the

T-cells A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell rec ...

or T-lymphocytes. After birth, the formation of blood stem cells shifts to the red

bone marrow Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It is composed of hematopoietic ce ...

. After 2–5 days, the umbilical vein and ductus venosus are obliterated; the former becomes the

round ligament of liver The round ligament of the liver (or ligamentum teres, or ligamentum teres hepatis) is a ligament that forms part of the free edge of the falciform ligament of the liver. It connects the liver to the umbilicus. It is the remnant of the left umbil ...

and the latter becomes the

. In the disorders of

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

and

portal hypertension Portal hypertension is abnormally increased portal venous pressure – blood pressure in the portal vein and its branches, that drain from most of the intestine to the liver. Portal hypertension is defined as a hepatic venous pressure gradient gr ...

, the umbilical vein can open up again.

Functions

The various functions of the liver are carried out by the liver cells or hepatocytes. The liver is thought to be responsible for up to 500 separate functions, usually in combination with other systems and organs. Currently, no

artificial organ An artificial organ is a human made organ device or tissue that is implanted or integrated into a human — interfacing with living tissue — to replace a natural organ, to duplicate or augment a specific function or functions so the patient m ...

or device is capable of reproducing all the functions of the liver. Some functions can be carried out by

, an experimental treatment for liver failure. The liver also accounts for about 20% of resting total body oxygen consumption.

Blood supply

The liver receives a dual blood supply from the hepatic portal vein and hepatic arteries. The hepatic portal vein delivers around 75% of the liver's blood supply and carries

venous blood Venous blood is deoxygenated blood which travels from the peripheral blood vessels, through the venous system into the right atrium of the heart. Deoxygenated blood is then pumped by the right ventricle to the lungs via the pulmonary artery whic ...

drained from the spleen, gastrointestinal tract, and its associated organs. The hepatic arteries supply arterial blood to the liver, accounting for the remaining quarter of its blood flow. Oxygen is provided from both sources; about half of the liver's oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries. The hepatic artery also has both alpha- and beta-adrenergic receptors; therefore, flow through the artery is controlled, in part, by the splanchnic nerves of the autonomic nervous system. Blood flows through the liver sinusoids and empties into the central vein of each lobule. The central veins coalesce into hepatic veins, which leave the liver and drain into the inferior vena cava. Liver veins.jpg, left, Liver veins– Liver vascular anatomy.svg, Diagram of liver, lobule, and portal tract and their inter-relations

Biliary flow

Diagram showing the position of the perihilar bile ducts CRUK 357

The

biliary tract The biliary tract, (biliary tree or biliary system) refers to the liver, gallbladder and bile ducts, and how they work together to make, store and secrete bile. Bile consists of water, electrolytes, bile acids, cholesterol, phospholipids and co ...

is derived from the branches of the bile ducts. The biliary tract, also known as the biliary tree, is the path by which bile is secreted by the liver then transported to the first part of the small intestine, the

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 m ...

. The bile produced in the liver is collected in

bile canaliculi Bile canaliculus (plural:bile canaliculi; also called bile capillaries) is a thin tube that collects bile secreted by hepatocytes. The bile canaliculi empty into a series of progressively larger bile ductules and ducts, which eventually become comm ...

, small grooves between the faces of adjacent hepatocytes. The canaliculi radiate to the edge of the liver lobule, where they merge to form bile ducts. Within the liver, these ducts are termed intrahepatic bile ducts, and once they exit the liver, they are considered extrahepatic. The intrahepatic ducts eventually drain into the right and left hepatic ducts, which exit the liver at the transverse fissure, and merge to form the common hepatic duct. The

cystic duct The cystic duct is the short duct that joins the gallbladder to the common hepatic duct. It usually lies next to the cystic artery. It is of variable length. It contains 'spiral valves of Heister', which do not provide much resistance to the ...

from the gallbladder joins with the common hepatic duct to form the common bile duct. The biliary system and connective tissue is supplied by the hepatic artery alone. Bile either drains directly into the duodenum via the common bile duct, or is temporarily stored in the gallbladder via the cystic duct. The common bile duct and the pancreatic duct enter the second part of the duodenum together at the hepatopancreatic ampulla, also known as the

ampulla of Vater The ampulla of Vater, also known as the or the hepatopancreatic duct, is formed by the union of the pancreatic duct and the common bile duct. The ampulla is specifically located at the major duodenal papilla. The ampulla of Vater is an import ...

Metabolism

The liver plays a major role in carbohydrate, protein, amino acid, and lipid metabolism.

Carbohydrate metabolism

The liver performs several roles in

carbohydrate metabolism Carbohydrate metabolism is the whole of the biochemistry, biochemical processes responsible for the metabolic anabolism, formation, catabolism, breakdown, and interconversion of carbohydrates in life, living organisms. Carbohydrates are central t ...

: * The liver synthesizes and stores around 100g of glycogen via

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 re ...

, the formation of glycogen from

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

. * When needed, the liver releases glucose into the blood by performing

glycogenolysis Glycogenolysis is the breakdown of glycogen (n) to glucose-1-phosphate and glycogen (n-1). Glycogen branches are catabolized by the sequential removal of glucose monomers via phosphorolysis, by the enzyme glycogen phosphorylase. Mechanism The ...

, the breakdown of glycogen into glucose. * The liver is also responsible for

gluconeogenesis Gluconeogenesis (GNG) is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. It is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms. In vertebrat ...

, which is the synthesis of glucose from certain

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s, lactate, or

glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...

. Adipose and liver cells produce glycerol by breakdown of fat, which the liver uses for gluconeogenesis. * Liver also does glyconeogenesis which is synthesis of

glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body. Glycogen functions as one o ...

from

lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...

Protein metabolism

The liver is responsible for the mainstay of protein

, synthesis as well as degradation. All

plasma proteins Blood-proteins, also termed plasma proteins, are proteins present in blood plasma. They serve many different functions, including transport of lipids, hormones, vitamins and minerals in activity and functioning of the immune system. Other blood p ...

except Gamma-globulins are synthesised in the liver. It is also responsible for a large part of

amino acid synthesis Amino acid synthesis is the set of biochemical processes (metabolic pathways) by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to sy ...

. The liver plays a role in the production of clotting factors, as well as red blood cell production. Some of the proteins synthesized by the liver include

coagulation factors Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...

I (fibrinogen), II (prothrombin), V,

VII VII or vii may refer to: the Roman numeral 7 Art and entertainment * The Vii, a video game console * vii, leading-tone triad, see diminished triad * ''VII'' (Blitzen Trapper album) * ''VII'' (Just-Ice album) * ''VII'' (Teyana Taylor album) * ...

, VIII, IX, X, XI, XII,

XIII XIII may refer to: * 13 (number) or XIII in Roman numerals * 13th century in Roman numerals * ''XIII'' (comics), a Belgian comic book series by Jean Van Hamme and William Vance ** ''XIII'' (2003 video game), a 2003 video game based on the comic b ...

, as well as

protein C Protein C, also known as autoprothrombin IIA and blood coagulation factor XIX, is a zymogen, that is, an inactive enzyme. The activated form plays an important role in regulating anticoagulation, inflammation, and apoptosis, cell death and ...

protein S Protein S (also known as PROS) is a vitamin K-dependent plasma glycoprotein synthesized in the liver. In the circulation, Protein S exists in two forms: a free form and a complex form bound to complement protein C4b-binding protein (C4BP). In huma ...

and

antithrombin Antithrombin (AT) is a small glycoprotein that inactivates several enzymes of the coagulation system. It is a 432-amino-acid protein produced by the liver. It contains three disulfide bonds and a total of four possible glycosylation sites. α-An ...

. The liver is a major site of production for

thrombopoietin Thrombopoietin (THPO) also known as megakaryocyte growth and development factor (MGDF) is a protein that in humans is encoded by the ''THPO'' gene. Thrombopoietin is a glycoprotein hormone produced by the liver and kidney which regulates the pro ...

, a

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...

hormone that regulates the production of

platelet Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ini ...

s by the bone marrow.

Lipid metabolism

The liver plays several roles in

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

metabolism: it performs

synthesis,

lipogenesis In biochemistry, lipogenesis is the conversion of fatty acids and glycerol into fats, or a metabolic process through which acetyl-CoA is converted to triglyceride for storage in fat. Lipogenesis encompasses both fatty acid and triglyceride syn ...

, and the production of

triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as w ...

s, and a bulk of the body's lipoproteins are synthesized in the liver. The liver plays a key role in digestion, as it produces and excretes

(a yellowish liquid) required for emulsifying fats and help the absorption of vitamin K from the diet. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder. The liver produces

insulin-like growth factor 1 Insulin-like growth factor 1 (IGF-1), also called somatomedin C, is a hormone similar in molecular structure to insulin which plays an important role in childhood growth, and has anabolic effects in adults. IGF-1 is a protein that in humans is ...

, a

polypeptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A p ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

hormone that plays an important role in childhood growth and continues to have anabolic effects in adults.

Breakdown

The liver is responsible for the breakdown of

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...

and other

s. The liver breaks down

bilirubin Bilirubin (BR) (Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the ...

via

glucuronidation Glucuronidation is often involved in drug metabolism of substances such as drugs, pollutants, bilirubin, androgens, estrogens, mineralocorticoids, glucocorticoids, fatty acid derivatives, retinoids, and bile acids. These linkages involve glycosid ...

, facilitating its excretion into bile. The liver is responsible for the breakdown and excretion of many waste products. It plays a key role in breaking down or modifying toxic substances (e.g.,

methylation In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These t ...

) and most medicinal products in a process called

drug metabolism Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set of ...

. This sometimes results in

toxication Toxication, toxification or toxicity exaltation is the conversion of a chemical compound into a more toxic form in living organisms or in substrates such as soil or water. The conversion can be caused by enzymatic metabolism in the organisms, as w ...

, 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 is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

into

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...

as part of the ornithine cycle or the urea cycle, and the urea is excreted in the urine.

Blood reservoir

Because the liver is an expandable organ, large quantities of blood can be stored in its blood vessels. Its normal blood volume, including both that in the hepatic veins and that in the hepatic sinuses, is about 450 milliliters, or almost 10 percent of the body's total blood volume. When high pressure in the right atrium causes backpressure in the liver, the liver expands, and 0.5 to 1 liter of extra blood is occasionally stored in the hepatic veins and sinuses. This occurs especially in cardiac failure with peripheral congestion. Thus, in effect, the liver is a large, expandable, venous organ capable of acting as a valuable blood reservoir in times of excess blood volume and capable of supplying extra blood in times of diminished blood volume.

Lymph production

Because the pores in the hepatic sinusoids are very permeable and allow ready passage of both fluid and proteins into the

, the

lymph Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to ...

draining from the liver usually has a protein concentration of about 6 g/dl, which is only slightly less than the protein concentration of plasma. Also, the high permeability of the liver sinusoid epithelium allows large quantities of lymph to form. Therefore, about half of all the lymph formed in the body under resting conditions arises in the liver.

Other

* The liver stores a multitude of substances, including

vitamin A Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably bet ...

(1–2 years' supply),

vitamin D Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group are vitamin D3 (c ...

(1–4 months' supply), vitamin B₁₂ (3–5 years' supply),

vitamin K Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation ...

vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitami ...

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pr ...

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

, etc. * Haemopoiesis - The formation of blood cells is called haemopoiesis. In embryonic stage RBC and WBC are formed by liver. In the first trimester fetus, the liver is the main site of

production. By the 32nd week of

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...

, the

has almost completely taken over that task. *Liver helps in purification of blood. The

Kupffer cell Kupffer cells, also known as stellate macrophages and Kupffer–Browicz cells, are specialized cells localized in the liver within the lumen of the liver sinusoids and are adhesive to their endothelial cells which make up the blood vessel walls. Ku ...

s of liver are

phagocytic cells Phagocytes are cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. Their name comes from the Greek ', "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell", from the Greek ' ...

, helps in phagocytosis of dead blood cells and bacteria from the blood. * The liver is responsible for immunological effects – the

mononuclear phagocyte system In immunology, the mononuclear phagocyte system or mononuclear phagocytic system (MPS) also known as the reticuloendothelial system or macrophage system is a part of the immune system that consists of the phagocytic cells located in reticular conn ...

of the liver contains many immunologically active cells, acting as a 'sieve' for antigens carried to it via the

portal system In the circulatory system of animals, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are co ...

. * The liver produces

albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ...

, the most abundant protein in

blood serum Serum () is the fluid and solute component of blood which does not play a role in clotting. It may be defined as blood plasma without the clotting factors, or as blood with all cells and clotting factors removed. Serum includes all proteins not u ...

. It is essential in the maintenance of

oncotic pressure Oncotic pressure, or colloid osmotic-pressure, is a form of osmotic pressure induced by the proteins, notably albumin, in a blood vessel's plasma (blood/liquid) that causes a pull on fluid back into the capillary. Participating colloids displace ...

, and acts as a transport for

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

s and

steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: corticosteroids (typically made in the adrenal cortex, hence ''cortico-'') and sex steroids (typically made in the gonads or placenta). Wi ...

s. * The liver synthesizes

angiotensinogen Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adren ...

, a hormone that is responsible for raising the

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...

when activated by

renin Renin (etymology and pronunciation), also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin–angiotensin–aldosterone system (RAAS)—also known as the r ...

, an enzyme that is released when the

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...

senses

low blood pressure Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dia ...

. * The liver produces the enzyme

catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting t ...

to break down

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

, a toxic

oxidising agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...

, into water and oxygen.

With aging

The oxidative capacity of the liver decreases with aging, and therefore any medications that require oxidation (for instance,

benzodiazepines Benzodiazepines (BZD, BDZ, BZs), sometimes called "benzos", are a class of depressant drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. They are prescribed to treat conditions such as anxiety disorders, i ...

) are more likely to accumulate to toxic levels. However, medications with shorter

half-lives Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

, such as

lorazepam Lorazepam, sold under the brand name Ativan among others, is a benzodiazepine medication. It is used to treat anxiety disorders, trouble sleeping, severe agitation, active seizures including status epilepticus, alcohol withdrawal, and c ...

and

oxazepam Oxazepam is a short-to-intermediate-acting benzodiazepine. Oxazepam is used for the treatment of anxiety and insomnia and in the control of symptoms of alcohol withdrawal syndrome. It is a metabolite of diazepam, prazepam, and temazepam, and ha ...

, are preferred in most cases when benzodiazepines are required in regard to

geriatric medicine Geriatrics, or geriatric medicine, is a medical specialty focused on providing care for the unique health needs of older adults. The term ''geriatrics'' originates from the Greek γέρων ''geron'' meaning "old man", and ιατρός ''iatros' ...

Clinical significance

Disease

The liver is a vital organ and supports almost every other organ in the body. Because of its strategic location and multidimensional functions, the liver is prone to many diseases. The bare area of the liver is a site that is vulnerable to the passing of infection from the abdominal cavity to the

thoracic cavity The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...

. Liver diseases may be diagnosed by

liver function tests Liver function tests (LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial thromboplastin ti ...

–blood tests that can identify various markers. For example, acute-phase reactants are produced by the liver in response to injury or inflammation.

Hepatitis Hepatitis is inflammation of the liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), poor appetite, vomiting, tiredness, abdominal pa ...

is a common condition of inflammation of the liver. The most usual cause of this is viral, and the most common of these infections are

hepatitis A Hepatitis A is an infectious disease of the liver caused by ''Hepatovirus A'' (HAV); it is a type of viral hepatitis. Many cases have few or no symptoms, especially in the young. The time between infection and symptoms, in those who develop them ...

, B, C, D, and E. Some of these infections are sexually transmitted. Inflammation can also be caused by other viruses in the family

Herpesviridae ''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπειν ...

such as the ''

herpes simplex virus Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), also known by their taxonomical names ''Human alphaherpesvirus 1'' and '' Human alphaherpesvirus 2'', are two members of the human ''Herpesviridae'' family, a set of viruses that produce viral inf ...

''. Chronic (rather than acute) infection with hepatitis B virus or hepatitis C virus is the main cause of

liver cancer Liver cancer (also known as hepatic cancer, primary hepatic cancer, or primary hepatic malignancy) is cancer that starts in the liver. Liver cancer can be primary (starts in liver) or secondary (meaning cancer which has spread from elsewhere to th ...

. Globally, about 248 million individuals are chronically infected with hepatitis B (with 843,724 in the U.S.), and 142 million are chronically infected with hepatitis C (with 2.7 million in the U.S.). Globally there are about 114 million and 20 million cases of hepatitis A and hepatitis E respectively, but these generally resolve and do not become chronic. Hepatitis D virus is a "satellite" of hepatitis B virus (it can only infect in the presence of hepatitis B), and co-infects nearly 20 million people with hepatitis B, globally.

Hepatic encephalopathy Hepatic encephalopathy (HE) is an altered level of consciousness as a result of liver failure. Its onset may be gradual or sudden. Other symptoms may include movement problems, changes in mood, or changes in personality. In the advanced stages ...

is caused by an accumulation of toxins in the bloodstream that are normally removed by the liver. This condition can result in coma and can prove fatal.

Budd–Chiari syndrome Budd–Chiari syndrome is a very rare condition, affecting one in a million adults. The condition is caused by occlusion of the hepatic veins that drain the liver. It presents with the classical triad of abdominal pain, ascites, and liver enlarge ...

is a condition caused by blockage of the

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

(including

thrombosis Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (thro ...

) that drain the liver. It presents with the classical triad of abdominal pain,

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

and liver enlargement. Many diseases of the liver are accompanied by

jaundice Jaundice, also known as icterus, is a yellowish or greenish pigmentation of the skin and sclera due to high bilirubin levels. Jaundice in adults is typically a sign indicating the presence of underlying diseases involving abnormal heme meta ...

caused by increased levels of

in the system. The bilirubin results from the breakup of the

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

of dead

s; normally, the liver removes bilirubin from the blood and excretes it through bile. Other disorders caused by excessive alcohol consumption are grouped under

alcoholic liver disease Alcoholic liver disease (ALD), also called alcohol-related liver disease (ARLD), is a term that encompasses the liver manifestations of alcohol overconsumption, including fatty liver, alcoholic hepatitis, and chronic hepatitis with liver fibrosis ...

s and these include

alcoholic hepatitis Alcoholic hepatitis is hepatitis (inflammation of the liver) due to excessive intake of alcohol. Patients typically have a history of at least 10 years of heavy alcohol intake, typically 8-10 drinks per day. It is usually found in association wit ...

fatty liver Fatty liver disease (FLD), also known as hepatic steatosis, is a condition where excess fat builds up in the liver. Often there are no or few symptoms. Occasionally there may be tiredness or pain in the upper right side of the abdomen. Complicat ...

, and

. Factors contributing to the development of alcoholic liver diseases are not only the quantity and frequency of alcohol consumption, but can also include gender, genetics, and liver insult. Liver damage can also be caused by drugs, particularly

paracetamol Paracetamol, also known as acetaminophen, is a medication used to treat fever and mild to moderate pain. Common brand names include Tylenol and Panadol. At a standard dose, paracetamol only slightly decreases body temperature; it is inferior ...

and drugs used to treat cancer. A rupture of the liver can be caused by a

liver shot A liver shot or liver punch 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 instantly. Th ...

used in combat sports.

Primary biliary cholangitis Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis, is an autoimmune disease of the liver. It results from a slow, progressive destruction of the small bile ducts of the liver, causing bile and other toxins to build ...

is an

autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...

of the liver. It is marked by slow progressive destruction of the small

s of the liver, with the intralobular ducts (

Canals of Hering The canals of Hering, or intrahepatic bile ductules, are part of the outflow system of exocrine bile product from the liver. Liver stem cells are located in the canals of Hering. Structure They are found between the bile canaliculi and interlobu ...

) affected early in the disease. When these ducts are damaged,

and other toxins build up in the liver (

cholestasis Cholestasis is a condition where bile cannot flow from the liver to the duodenum. The two basic distinctions are an obstructive type of cholestasis where there is a mechanical blockage in the duct system that can occur from a gallstone or malignan ...

) and over time damages the liver tissue in combination with ongoing immune related damage. This can lead to scarring (

fibrosis Fibrosis, also known as fibrotic scarring, is a pathological wound healing in which connective tissue replaces normal parenchymal tissue to the extent that it goes unchecked, leading to considerable tissue remodelling and the formation of perma ...

) and

. Cirrhosis increases the resistance to blood flow in the liver, and can result in

. Congested anastomoses between the

portal venous system In the circulatory system of animals, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are co ...

and the systemic circulation, can be a subsequent condition. There are also many pediatric liver diseases, including

biliary atresia Biliary atresia, also known as extrahepatic ductopenia and progressive obliterative cholangiopathy, is a childhood disease of the liver in which one or more bile ducts are abnormally narrow, blocked, or absent. It can be congenital or acquired. I ...

alpha-1 antitrypsin deficiency Alpha-1 antitrypsin deficiency (A1AD or AATD) is a genetic disorder that may result in lung disease or liver disease. Onset of lung problems is typically between 20 and 50 years of age. This may result in shortness of breath, wheezing, or an inc ...

alagille syndrome Alagille syndrome is a genetic disorder that affects primarily the liver and the heart. Problems associated with the disorder generally become evident in infancy or early childhood. The disorder is inherited in an autosomal dominant pattern, and t ...

progressive familial intrahepatic cholestasis Progressive familial intrahepatic cholestasis (PFIC) is a group of familial cholestatic conditions caused by defects in biliary epithelial transporters. The clinical presentation usually occurs first in childhood with progressive cholestasis. Thi ...

Langerhans cell histiocytosis Langerhans cell histiocytosis (LCH) is an abnormal clonal proliferation of Langerhans cells, abnormal cells deriving from bone marrow and capable of migrating from skin to lymph nodes. Symptoms range from isolated bone lesions to multisystem dise ...

and hepatic hemangioma a

benign tumour A benign tumor is a mass of cells (tumor) that does not invade neighboring tissue or metastasize (spread throughout the body). Compared to malignant (cancerous) tumors, benign tumors generally have a slower growth rate. Benign tumors have re ...

the most common type of liver tumour, thought to be congenital. A genetic disorder causing multiple cysts to form in the liver tissue, usually in later life, and usually asymptomatic, is

polycystic liver disease Polycystic liver disease (PLD) usually describes the presence of multiple cysts scattered throughout normal liver tissue. PLD is commonly seen in association with autosomal-dominant polycystic kidney disease, with a prevalence of 1 in 400 to 1000, ...

. Diseases that interfere with liver function will lead to derangement of these processes. However, the liver has a great capacity to regenerate and has a large reserve capacity. In most cases, the liver only produces symptoms after extensive damage.

Hepatomegaly Hepatomegaly is the condition of having an enlarged liver. It is a non-specific medical sign having many causes, which can broadly be broken down into infection, hepatic tumours, or metabolic disorder. Often, hepatomegaly will present as an abdomi ...

refers to an enlarged liver and can be due to many causes. It can be

palpated Palpation is the process of using one's hands to check the body, especially while perceiving/diagnosing a disease or illness. Usually performed by a health care practitioner, it is the process of feeling an object in or on the body to determine ...

in a

liver span The liver span is a measurement performed during physical examination to determine the size of the liver and identify possible hepatomegaly. It is the distance between the lower border of the liver in the mid-clavicular line obtained by palpation ...

measurement.

Symptoms

The classic symptoms of liver damage include the following: * Pale stools occur when

stercobilin Stercobilin is a tetrapyrrolic bile pigment and is one end-product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: A cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. Kay IT, Weimer M, Watson CJ (1963)� ...

, 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

deposits in skin, causing an intense

itch Itch (also known as pruritus) is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to be classified as any one type of sensory experience. Itch has many similarities to pain, and while both are unpleasant ...

. Itching is the most common complaint by people who have liver failure. Often this itch cannot be relieved by drugs. * Swelling of the abdomen, and swelling of the ankles and feet occurs because the liver fails to make albumin. * Excessive fatigue occurs from a generalized loss of nutrients,

minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

and vitamins. *

Bruising A bruise, also known as a contusion, is a type of hematoma of tissue, the most common cause being capillaries damaged by trauma, causing localized bleeding that extravasates into the surrounding interstitial tissues. Most bruises occur clos ...

and easy bleeding are other features of liver disease. The liver makes

clotting factors Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism ...

, substances which help prevent bleeding. When liver damage occurs, these factors are no longer present and severe bleeding can occur. * Pain in the upper right quadrant can result from the stretching of Glisson's capsule in conditions of

hepatitis Hepatitis is inflammation of the liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), poor appetite, vomiting, tiredness, abdominal pa ...

and

pre-eclampsia Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease ...

Diagnosis

The diagnosis of liver disease is made by

, groups of

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 hypodermic needle, or via fingerprick. Multiple tests for specific blood components, such as a glucose test or a cholester ...

s, that can readily show the extent of liver damage. If

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

is suspected, then other

serological Serology is the scientific study of serum and other body fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection (against a given mi ...

tests will be carried out. A physical examination of the liver can only reveal its size and any tenderness, and some form of

imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of an image). Imaging technology is the application of materials and methods to create, preserve, or duplicate images. ...

such as an

ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...

or CT scan may also be needed. Sometimes a

liver biopsy Liver biopsy is the biopsy (removal of a small sample of tissue) 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. Medica ...

will be necessary, and a tissue sample is taken through a needle inserted into the skin just below the

rib cage The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...

. This procedure may be helped by a sonographer providing ultrasound guidance to an interventional radiologist. File:Axial CT anomalous hepatic veins.jpg, Axial CT image showing anomalous hepatic veins coursing on the subcapsular anterior surface of the liver. File:Anterior MIP image of anomalous hepatic veins.jpg, Maximum intensity projection (MIP) CT image as viewed anteriorly showing the anomalous hepatic veins coursing on the anterior surface of the liver File:Lateral MIP CT of anomalous surface hepatic veins.jpg, Lateral MIP view in the same patient File:CTscanofmyLiver.jpg, A CT scan in which the liver and portal vein are shown.

Liver regeneration

The liver is the only human internal organ capable of natural

regeneration Regeneration may refer to: Science and technology * Regeneration (biology), the ability to recreate lost or damaged cells, tissues, organs and limbs * Regeneration (ecology), the ability of ecosystems to regenerate biomass, using photosynthesis ...

of lost tissue; as little as 25% of a liver can regenerate into a whole liver. This is, however, not true regeneration but rather

compensatory growth Compensatory growth, known as catch-up growth and compensatory gain, is an accelerated growth of an organism following a period of slowed development, particularly as a result of nutrient deprivation. The growth may be with respect to weight or ...

in mammals. 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. In some other species, such as zebrafish, the liver undergoes true regeneration by restoring both shape and size of the organ. In the liver, large areas of the tissues are formed but for the formation of new cells there must be sufficient amount of material so the circulation of the blood becomes more active. This is predominantly due to the

s re-entering the

cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and subs ...

. That is, the hepatocytes go from the quiescent

G0 phase The G0 phase describes a cellular state outside of the replicative cell cycle. Classically, cells were thought to enter G0 primarily due to environmental factors, like nutrient deprivation, that limited the resources necessary for proliferation ...

to the

G1 phase The G1 phase, gap 1 phase, or growth 1 phase, is the first of four phases of the cell cycle that takes place in eukaryotic cell division. In this part of interphase, the cell synthesizes mRNA and proteins in preparation for subsequent steps leadi ...

and undergo mitosis. This process is activated by the p75 receptors. There is also some evidence of

bipotential Pluripotency: These are the cells that can generate into any of the three Germ layers which imply Endodermal, Mesodermal, and Ectodermal cells except tissues like the placenta. According to Latin terms, Pluripotentia means the ability for many thin ...

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type o ...

s, called hepatic oval cells or ovalocytes (not to be confused with oval red blood cells of

ovalocytosis Southeast Asian ovalocytosis is a blood disorder that is similar to, but distinct from hereditary elliptocytosis. It is common in some communities in Malaysia and Papua New Guinea, as it confers some resistance to cerebral Falciparum Malaria. Pa ...

), which are thought to reside in the

canals of Hering The canals of Hering, or intrahepatic bile ductules, are part of the outflow system of exocrine bile product from the liver. Liver stem cells are located in the canals of Hering. Structure They are found between the bile canaliculi and interlobu ...

. These cells can differentiate into either

s or

cholangiocyte Cholangiocytes are the epithelial cells of the bile duct. They are cuboidal epithelium in the small interlobular bile ducts, but become columnar and HCO3:-secreting in larger bile ducts approaching the porta hepatis and the extrahepatic ducts. T ...

s. Cholangiocytes are the epithelial lining cells of the

s. They are cuboidal epithelium in the small interlobular bile ducts, but become columnar and mucus secreting in larger bile ducts approaching the porta hepatis and the extrahepatic ducts. Research is being carried out on the use of stem cells for the generation of an artificial liver. Scientific and medical works about liver regeneration often refer to the Greek Titan

Prometheus In Greek mythology, Prometheus (; , , possibly meaning "forethought")Smith"Prometheus". is a Titan god of fire. Prometheus is best known for defying the gods by stealing fire from them and giving it to humanity in the form of technology, know ...

who was chained to a rock in the

Caucasus The Caucasus () or Caucasia (), is a region between the Black Sea and the Caspian Sea, mainly comprising Armenia, Azerbaijan, Georgia, and parts of Southern Russia. The Caucasus Mountains, including the Greater Caucasus range, have historically ...

where, each day, his liver was devoured by an eagle, only to grow back each night. The myth suggests the

ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cultu ...

may have known about the liver's remarkable capacity for self-repair.

Liver transplantation

Human liver transplants were first performed by

Thomas Starzl Thomas Earl Starzl (March 11, 1926 – March 4, 2017) was an American physician, researcher, and expert on organ transplants. He performed the first human liver transplants, and has often been referred to as "the father of modern transplantatio ...

in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

and

Roy Calne Sir Roy Yorke Calne, FRCP, FRCS, FRS (born 30 December 1930) is a British surgeon and pioneer in organ transplantation. Career His most notable achievements are the world's first liver, heart, and lung transplant together with John Wallwor ...

Cambridge Cambridge ( ) is a university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cambridge bec ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

in 1963 and 1967, respectively. Liver

Liver transplantation Liver transplantation or hepatic transplantation is the replacement of a diseased liver with the healthy liver from another person (allograft). Liver transplantation is a treatment option for end-stage liver disease and acute liver failure, al ...

is the only option for those with irreversible liver failure. Most transplants are done for chronic liver diseases leading to

, such as chronic

hepatitis C Hepatitis C is an infectious disease caused by the hepatitis C virus (HCV) that primarily affects the liver; it is a type of viral hepatitis. During the initial infection people often have mild or no symptoms. Occasionally a fever, dark urine, a ...

alcoholism Alcoholism is, broadly, any drinking of alcohol (drug), alcohol that results in significant Mental health, mental or physical health problems. Because there is disagreement on the definition of the word ''alcoholism'', it is not a recognize ...

, and autoimmune hepatitis. Less commonly, liver transplantation is done for

fulminant hepatic failure Acute liver failure is the appearance of severe complications rapidly after the first signs (such as jaundice) of liver disease, and indicates that the liver has sustained severe damage (loss of function of 80–90% of liver cells). The complicat ...

, in which liver failure occurs rapidly over a period of days or weeks. Liver

allograft Allotransplant (''allo-'' meaning "other" in Greek) is the transplantation of cells, tissues, or organs to a recipient from a genetically non-identical donor of the same species. The transplant is called an allograft, allogeneic transplant, o ...

s for transplant usually come from donors who have died from fatal

brain injury An injury is any physiological damage to living tissue caused by immediate physical stress. An injury can occur intentionally or unintentionally and may be caused by blunt trauma, penetrating trauma, burning, toxic exposure, asphyxiation, or o ...

Living donor liver transplantation Liver transplantation or hepatic transplantation is the replacement of a diseased liver with the healthy liver from another person (allograft). Liver transplantation is a treatment option for end-stage liver disease and acute liver failure, al ...

is a technique in which a portion of a living person's liver is removed (

hepatectomy Hepatectomy is the surgical resection (removal of all or part) of the liver. While the term is often employed for the removal of the liver from a liver transplant donor, this article will focus on partial resections of hepatic tissue and hepatopo ...

) 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, 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 were at least two donor deaths out of the first several hundred cases. A 2006 publication addressed the problem of donor mortality and found at least fourteen cases. 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 (MDCT) and

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

(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. File:LDLTA.jpg, MDCT image. Arterial anatomy contraindicated for liver donation File:LDLTP.jpg, MDCT image. Portal venous anatomy contraindicated for liver donation File:LDLT volume measure.jpg, MDCT image. 3D image created by MDCT can clearly visualize the liver, measure the liver volume, and plan the dissection plane to facilitate the liver transplantation procedure. File:R vs L Liver by CT.PNG, Phase contrast CT image. Contrast is perfusing the right liver but not the left due to a left portal vein thrombus.

Society and culture

Some cultures regard the liver as the seat of the

soul In many religious and philosophical traditions, there is a belief that a soul is "the immaterial aspect or essence of a human being". Etymology The Modern English noun ''soul'' is derived from Old English ''sāwol, sāwel''. The earliest attes ...

. In

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the Cosmogony, origin and Cosmology#Metaphysical co ...

, the gods punished

for revealing fire to humans by chaining him to a rock where a

vulture A vulture is a bird of prey that scavenges on carrion. There are 23 extant species of vulture (including Condors). Old World vultures include 16 living species native to Europe, Africa, and Asia; New World vultures are restricted to North and ...

(or an

eagle Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, just ...

) 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 (from Latin ''divinare'', 'to foresee, to foretell, to predict, to prophesy') is the attempt to gain insight into a question or situation by way of an occultic, standardized process or ritual. Used in various forms throughout histor ...

called

haruspicy In the religion of ancient Rome, a haruspex (plural haruspices; also called aruspex) was a person trained to practise a form of divination called haruspicy (''haruspicina''), the inspection of the entrails (''exta''—hence also extispicy ( ...

hepatomancy In the religion of ancient Rome, a haruspex (plural haruspices; also called aruspex) was a person trained to practise a form of divination called haruspicy (''haruspicina''), the inspection of the entrails ('' exta''—hence also extispicy ...

, 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 The Talmud (; he, , Talmūḏ) is the central text of Rabbinic Judaism and the primary source of Jewish religious law (''halakha'') and Jewish theology. Until the advent of modernity, in nearly all Jewish communities, the Talmud was the cente ...

(tractate ''Berakhot 61b'') refers to the liver as the seat of

anger Anger, also known as wrath or rage, is an intense emotional state involving a strong uncomfortable and non-cooperative response to a perceived provocation, hurt or threat. A person experiencing anger will often experience physical effects, su ...

, with the

counteracting this. The

Persian Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, the majority ethnic group in Iran, not to be conflated with the Iranic peoples ** Persian language, an Iranian language of the ...

Urdu Urdu (;"Urdu"
''

Hindi Hindi (Devanāgarī: or , ), or more precisely Modern Standard Hindi (Devanagari: ), is an Indo-Aryan language spoken chiefly in the Hindi Belt region encompassing parts of northern, central, eastern, and western India. Hindi has been de ...

languages ( or or ) refer to the liver in figurative speech to indicate courage and strong feelings, or "their best"; e.g., "This

Mecca Mecca (; officially Makkah al-Mukarramah, commonly shortened to Makkah ()) is a city and administrative center of the Mecca Province of Saudi Arabia, and the Holiest sites in Islam, holiest city in Islam. It is inland from Jeddah on the Red ...

has thrown to you the pieces of its liver!". The term , literally "the strength (power) of my liver", is a term of endearment in Urdu. In Persian slang, is used as an adjective for any object which is desirable, especially women. In the

Zulu language Zulu (), or isiZulu as an endonym, is a Southern Bantu language of the Nguni branch spoken in Southern Africa. It is the language of the Zulu people, with about 12 million native speakers, who primarily inhabit the province of KwaZulu-Natal o ...

, the word for liver () is the same as the word for courage. In English the term 'lily-livered' is used to indicate cowardice from the medieval belief that the liver was the seat of courage. Spanish also means "courage". However the secondary meaning of Basque is "indolence". In biblical Hebrew, the word for liver, (, stemmed or , similar to Arabic ), also means heavy and is used to describe the rich ("heavy" with possessions) and honor (presumably for the same reason). In the Book of Lamentations (2:11) it is used to describe the physiological responses to sadness by "my liver spilled to earth" along with the flow of tears and the overturning in bitterness of the intestines. On several occasions in the

book of Psalms The Book of Psalms ( or ; he, תְּהִלִּים, , lit. "praises"), also known as the Psalms, or the Psalter, is the first book of the ("Writings"), the third section of the Tanakh, and a book of the Old Testament. The title is derived f ...

(most notably Psalm 16, 16:9), the word is used to describe happiness in the liver, along with the heart (which beats rapidly) and the flesh (which appears red under the skin). Further usage as the self (similar to "your honor") is widely available throughout the old testament, sometimes compared to the breathing soul (Genesis 49:6, Psalms 7:6, etc.). An honorable hat was also referred to with this word (Job 19:9, etc.) and under that definition appears many times along with - grandeur. These four meanings were used in preceding ancient Afro-Asiatic languages such as Akkadian language, Akkadian and Ancient Egyptian preserved in classical Ethiopic Ge'ez language.

Food

Humans commonly eat the livers of mammals, fowl, and fish as food. Domestic pig, ox, lamb, calf, chicken, and goose livers are widely available from butchers and supermarkets. In the Romance languages, the anatomical word for "liver" (French language, French ''foie'', Spanish language, Spanish ''hígado'', etc.) derives not from the Latin language, Latin anatomical term, ''jecur'', but from the culinary term ''ficatum'', literally "stuffed with figs," referring to the livers of geese that had been fattened on figs. Animal livers are rich in iron, Retinol, vitamin A and Vitamin B12, vitamin B₁₂; and cod liver oil is commonly used as a dietary supplement. Liver can be baked, boiled, broiled, fried, stir-fried, or eaten raw (''asbeh nayeh'' or ''sawda naye'' in Lebanese cuisine, or liver sashimi in Japanese cuisine). In many preparations, pieces of liver are combined with pieces of meat or kidneys, as in the various forms of Middle Eastern mixed grill (e.g. ''meurav Yerushalmi''). Well-known examples include liver pâté, foie gras, chopped liver, and leverpastej. Liver sausages, such as Braunschweiger (sausage), Braunschweiger and liverwurst, are also a valued meal. Liver sausages may also be used as spreads. A traditional South African delicacy, skilpadjies, is made of minced lamb's liver wrapped in ''netvet'' (caul fat), and grilled over an open fire. Traditionally, some fish livers were valued as food, especially the Common stingray, stingray liver. It was used to prepare delicacies, such as poached skate liver on toast in England, as well as the ''beignets de foie de raie'' and ''foie de raie en croute'' in French cuisine.

Giraffe liver

The Humur, Humr are one of the tribes in the Baggara ethnic group, native to southwestern Kordofan in Sudan who speak Shuwa Arabic, ''Shuwa'' (Chadian Arabic), make a non-alcoholic drink from the liver and

of the giraffe, which they call ''umm nyolokh''. They claim it is intoxicating (Arabic سكران ''sakran''), causing dreams and even waking hallucinations. Anthropologist Ian Cunnison accompanied the Humr on one of their giraffe-hunting expeditions in the late 1950s, and noted that: :It is said that a person, once he has drunk ''umm nyolokh'', will return to giraffe again and again. Humr, being Ansar (Sudan), Mahdists, are strict Khamr, abstainers [from alcohol] and a Humrawi is never drunk (''sakran'') on liquor or beer. But he uses this word to describe the effects which ''umm nyolokh'' has upon him. Cunnison's remarkable account of an apparently psychoactive mammal found its way from a somewhat obscure scientific paper into more mainstream literature through a conversation between Wendy James (anthropologist), W. James of the Institute of Social and Cultural Social anthropology, Anthropology at the University of Oxford and specialist on the use of hallucinogens and intoxicants in society, and Richard Rudgley, R. Rudgley, who discussed it in a book on psychoactive drugs for general readers. He speculated that a hallucinogenic compound N,N-Dimethyltryptamine in the giraffe liver might account for the intoxicating properties claimed for ''umm nyolokh''. Cunnison, on the other hand, writing in 1958 found it hard to believe in the literal truth of the Humr's assertion that the drink was intoxicating: :I can only assume that there is no intoxicating substance in the drink, and that the effect it produces is simply a matter of convention, although it may be brought about placebo, subconsciously. The study of entheogens in general – including entheogens of animal origin (e.g. hallucinogenic fish and Colorado River toad, toad venom) – has, however, made considerable progress in the sixty-odd years since Cunnison's report; the idea that some intoxicating substance might reside in giraffe livers may no longer be as far-fetched as it seemed to Cunnison. However, to date, proof (or disproof) still waits on detailed analyses of the organ and the beverage made from it.

Arrow/bullet poison

Certain Tungusic peoples of northeast Asia formerly prepared a type of arrow poison from rotting animal livers, which was, in later times, also applied to bullets. Russian anthropologist S. M. Shirokogoroff wrote that: :Formerly the using of poisoned arrows was common. For instance, among the Kumarčen, [a subgroup of the Oroqen people, Oroqen] even in recent times, a poison was used which was prepared from decaying liver. :[Note] This has been confirmed by the Kumarčen. I am not competent to judge as to the chemical conditions of production of poison which is not destroyed by the heat of explosion. However, the Tungus themselves compare this method [of poisoning ammunition] with the poisoning of arrows.

Other animals

The liver is found in all vertebrates and is typically the largest internal organ. The internal structure of the liver is broadly similar in all vertebrates, though 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 snakes, where the shape of the body necessitates a simple cigar-like form. An organ sometimes referred to as a liver is found associated with the digestive tract of the primitive chordate ''Amphioxus''. Although it performs many functions of a liver, it is not considered a "true" liver but rather a homology (biology), ''homolog'' of the vertebrate liver. The amphioxus hepatic caecum produces the liver-specific proteins vitellogenin,

, plasminogen, alanine aminotransferase, and

/Insulin-like growth factor (IGF)

References

Works cited

* *

External links

Liver at the Human Protein Atlas

VIRTUAL Liver – online learning resource

Liver enzymes
* with several diagrams. * doi:10.53347/rID-96561, Beaver tail liver {{Authority control Liver, Organs (anatomy)

Structure

Gross anatomy

Lobes

Surfaces

Impressions

Microscopic anatomy

Functional anatomy

Couinaud classification system

Gene and protein expression

Development

Fetal blood supply

Functions

Blood supply

Biliary flow

Metabolism

Carbohydrate metabolism

Protein metabolism

Lipid metabolism

Breakdown

Blood reservoir

Lymph production

Other

With aging

Clinical significance

Disease

Symptoms

Diagnosis

Liver regeneration

Liver transplantation

Society and culture

Food

Giraffe liver

Arrow/bullet poison

Other animals

See also

References

Works cited

External links