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Liver - Anatomy & Physiology (view source)
Revision as of 15:39, 27 October 2022
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[[Image:Pig Liver Topography.jpg|thumb|right|3000px|Liver Topography (Pig) - Copyright Nottingham 2008]]
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[[Image:Pig Liver Topography.jpg|thumb|right|300px|Liver Topography (Pig) - Copyright Nottingham 2008]]
==Introduction==
==Introduction==
The liver (hepar) is an extremely important organ in the body of mammals and vertebrates as it provides functions essential for life. It is the largest internal organ and has numerous functions including production of bile and protein, fat and carbohydrate metabolism. During foetal development, the liver has an important haemopoetic function, producing red and white blood cells from tissue between the hepatic cells and vessel walls.
The liver (hepar) is an extremely important organ in the body of mammals and vertebrates as it provides functions essential for life. It is the largest internal organ and has numerous functions including production of bile and protein, fat and carbohydrate metabolism. During foetal development, the liver has an important haemopoetic function, producing red and white blood cells from tissue between the hepatic cells and vessel walls.
The size of the liver varies due to its role in metabolism. In carnivores the liver weighs about 3-5% of body weight, in omnivores 2-3% and in herbivores 1.5%. the liver is much heavier in young animals than older animals as it atropies with age.
The size of the liver varies due to its role in metabolism. In carnivores the liver weighs about 3-5% of body weight, in omnivores 2-3% and in herbivores 1.5%. the liver is much heavier in young animals than older animals as it atrophies with age.
The liver is derived from an outpocketing of endoderm epithelium on the ventral duodenum from the caudal part of the foregut. The connection to the gut narrows to become the bile duct. The parenchymal tissue of the liver is formed from proliferating epithelial cords or strands which integrate with the blood sinuses of the umbilical and vitelline veins.
The liver is derived from an outpocketing of endoderm epithelium on the ventral duodenum from the caudal part of the foregut. The connection to the gut narrows to become the bile duct. The parenchymal tissue of the liver is formed from proliferating epithelial cords or strands which integrate with the blood sinuses of the umbilical and vitelline veins.
[[Image:Topography of the Liver.jpg|thumb|right|250px|Topography of the Liver (Dog)- Copyright RVC 2008]]
[[Image:Topography of the Liver.jpg|thumb|right|250px|Topography of the Liver (Dog)- Copyright RVC 2008]]
The liver is located in the cranial part of the abdomen. It us immediately caudal to the diaphragm and cranial to the [[Monogastric Stomach - Anatomy & Physiology|stomach]] and intestines. Generally the bulk of the liver is on the right of the midline. It is divided into lobes by fissures. Cranially the liver is convex, called the diaphragmatic surface. Caudally the liver is concave, called the visceral surface. The caudate lobe has a renal impression from the right [[Urinary System - Anatomy & Physiology#Upper Urinary Tract|kidney]]. The gastric impression occupies the whole of the left half of the visceral face. The [[Duodenum - Anatomy & Physiology|duodenal]] impression at the junction of the right and quadrate lobes continues onto the right lateral and caudate lobes. Passages or notches on the median plane allow the caudal vena cava and [[Oesophagus - Anatomy & Physiology|oesophagus]] to pass by. The [[Gall Bladder - Anatomy & Physiology|gall bladder]] is located between the right medial and quadrate lobes. '''Reticular fibres''' (collagen type III, proteoglycans and glycoproteins) support the hepatocytes and walls of the sinusoids. Interlobular spaces support bile ducts and blood vessels. The lesser omentum (often fat filled) is on the visceral surface between the left lateral lobe, heptic porta and lesser curvature of the [[Monogastric Stomach - Anatomy & Physiology|stomach]]. There is a oesophageal notch where the [[Oesophagus - Anatomy & Physiology|oesophagus]] passes over the liver.
The liver is located in the cranial part of the abdomen. It is immediately caudal to the diaphragm and cranial to the [[Monogastric Stomach - Anatomy & Physiology|stomach]] and intestines. Generally the bulk of the liver is on the right of the midline. It is divided into lobes by fissures. Cranially the liver is convex, called the diaphragmatic surface. Caudally the liver is concave, called the visceral surface. The caudate lobe has a renal impression from the right [[Urinary System Overview - Anatomy & Physiology#Upper Urinary Tract|kidney]]. The gastric impression occupies the whole of the left half of the visceral face. The [[Duodenum - Anatomy & Physiology|duodenal]] impression at the junction of the right and quadrate lobes continues onto the right lateral and caudate lobes. Passages or notches on the median plane allow the caudal vena cava and [[Oesophagus - Anatomy & Physiology|oesophagus]] to pass by. The [[Gall Bladder - Anatomy & Physiology|gall bladder]] is located between the right medial and quadrate lobes. '''Reticular fibres''' (collagen type III, proteoglycans and glycoproteins) support the hepatocytes and walls of the sinusoids. Interlobular spaces support bile ducts and blood vessels. The lesser omentum (often fat filled) is on the visceral surface between the left lateral lobe, heptic porta and lesser curvature of the [[Monogastric Stomach - Anatomy & Physiology|stomach]]. There is a oesophageal notch where the [[Oesophagus - Anatomy & Physiology|oesophagus]] passes over the liver.
==Divisions of the Liver==
==Divisions of the Liver==
==Ligaments==
==Ligaments==
The '''coronary ligament''' attaches the liver (from the diaphragmatic surface) to the diaphragm. It is an irregular fold of peritoneum. It surounds the triangular base of the diaphragmatic surface. It is continuous with outer most layer of the caudal vena cava.
The '''coronary ligament''' attaches the liver (from the diaphragmatic surface) to the diaphragm. It is an irregular fold of peritoneum. It surrounds the triangular base of the diaphragmatic surface. It is continuous with outer most layer of the caudal vena cava.
The '''falciform ligament''' is ventral to the coronary ligament. It is a fat filled embryological remnant of the fetal blood vessels from the placenta. It causes problems for surgical entry into the abdomen. It is located cranial to the umbilicus and is a vestige of the umbilical vein.
The '''falciform ligament''' is ventral to the coronary ligament. It is a fat filled embryological remnant of the fetal blood vessels from the placenta. It causes problems for surgical entry into the abdomen. It is located cranial to the umbilicus and is a vestige of the umbilical vein.
The '''triangular ligament''' is on the right and left sides of the coronary ligament.
The '''triangular ligament''' is on the right and left sides of the coronary ligament.
The liver has a dual blood supply. 70-80% via the hepatic portal vein (nutrient rich) and 20-30% via the hepatic artery (oxygen rich). It has a large blood supply (nearly a 1/3 of cardiac output passes through the liver).
The liver has a dual blood supply. 70-80% via the hepatic portal vein (nutrient rich) and 20-30% via the hepatic artery (oxygen rich). It has a large blood supply (nearly a 1/3 of cardiac output passes through the liver).
The '''hepatic artery''' is a branch of the caeliac artery. The '''portal vein''' is formed by tributaries draining the spleen, pancreas and digestive tract. '''Intrahepatic arteries''' combine with '''portal vein''' branches to supply the connective tissue and hepatic sinusoids of the liver. Blood flows from the portal areas into the central vein. The central vein is lined by simple squamous epithelium. The bile duct, blood vessels (including the important hepatic vein) and nerves enter and leave the liver at the hepatic porta. Blood from the central vein opens into the caudal vena cava. Liver circulation is controlled by interarterial, intervenous, arteriovenous, and by sphincter mechanisms, allowing carefull reglulation.
The '''hepatic artery''' is a branch of the caeliac artery. The '''portal vein''' is formed by tributaries draining the [[Spleen - Anatomy & Physiology|spleen]], [[Pancreas - Anatomy & Physiology|pancreas]] and digestive tract. '''Intrahepatic arteries''' combine with '''portal vein''' branches to supply the connective tissue and hepatic sinusoids of the liver. Blood flows from the portal areas into the central vein. The central vein is lined by simple squamous epithelium. The bile duct, blood vessels (including the important hepatic vein) and nerves enter and leave the liver at the hepatic porta. Blood from the central vein opens into the caudal vena cava. Liver circulation is controlled by interarterial, intervenous, arteriovenous, and by sphincter mechanisms, allowing careful regulation.
==Innervation==
==Innervation==
==Bile Acids==
==Bile Acids==
Bile acids are composed of cholesterol, bile acids and steroids. The main bile acid is '''cholic acid''' (C24). Conjugated to taurine or glycine in the liver to reduce pKa so they exist in an ionised form as bile salts. Bile salts conjugate with cholesterol and phospholipids and are then secreted into the bile. 95% are recycled in enterohepatic circulation. They emulsify fats which helps absorb fat soluble vitamins. In aqueous solution, they form micelles which are amphiphilic and can transport free fatty acids across the brush border.
Bile acids are composed of cholesterol, bile acids and steroids. The main bile acid is '''cholic acid''' (C24). Conjugated to taurine or glycine in the liver to reduce pKa so they exist in an ionised form as bile salts. Bile salts conjugate with cholesterol and phospholipids and are then secreted into the bile. They emulsify fats which helps absorb fat soluble vitamins. In aqueous solution, they form micelles which are amphiphilic and can transport free fatty acids across the brush border.
==Species Differences==
==Species Differences==
[[Image:Canine Liver Topography.jpg|thumb|right|250px|Liver Topography (Dog) - Copyright Nottingham 2008]]
[[Image:Canine Liver Topography.jpg|thumb|right|250px|Liver Topography (Dog) - Copyright Nottingham 2008]]
===Canine & Feline===
===Canine & Feline===
Both the left and right lobes are subdivided. Complete obstruction of the hepatic artery is fatal. The liver is almost entirely intra-thoracic. An enlarged caudate process contacts the right [[Urinary System - Anatomy & Physiology#Upper Urinary Tract|kidney]].
Both the left and right lobes are subdivided. Complete obstruction of the hepatic artery is fatal. The liver is almost entirely intra-thoracic. An enlarged caudate process contacts the right [[Urinary System Overview - Anatomy & Physiology#Upper Urinary Tract|kidney]].
===Equine===
===Equine===
===Porcine===
===Porcine===
The liver has deep interlobular fissures and a large amount of interlobular connective tissue. It has a mottled appearance. A Deep interlobular fissure divides the lived into 4 lobes- the left, right, medial and lateral. There is a small caudate lobe (which does not contact the [[Urinary System - Anatomy & Physiology#Upper urinary Tract|kidney]] so no renal impression). It is mostly on the right of the midline and has no papillary lobe.
The liver has deep interlobular fissures and a large amount of interlobular connective tissue. It has a mottled appearance. A Deep interlobular fissure divides the liver into 4 lobes- the left, right, medial and lateral. There is a small caudate lobe (which does not contact the [[Urinary System Overview - Anatomy & Physiology#Upper urinary Tract|kidney]] so no renal impression). It is mostly on the right of the midline and has no papillary lobe.
===Ruminants===
===Ruminants===
See [[Avian Liver - Anatomy & Physiology|avian liver]]
See [[Avian Liver - Anatomy & Physiology|avian liver]]
==Links==
==Histology==
[[Image:Lobule Histology.jpg|thumb|right|250px|Liver Lobule Histology - from [[Gastrointestinal Tract Histology resource|GIT-2 tutorial]] ]]
The larger liver cells are called '''lobules'''. Each lobule contains an opening for the '''central vein''' and contains portal areas. The lobules are composed of liver cords called '''hepatocytes'''. Sinusoids are present between hepatocytes containing red blood cells. There is a connective tissue capsule around each liver lobule. A thin '''mesothelium''' covers the connective tissue layer.
The '''portal area''' present in the lobules contains the '''hepatic artery''', which has thick walls and a small diameter and the '''hepatic vein''', which has thin walls and a large and irregular shape. It also contains '''bile ducts''', with cuboidal or columnar epithelium and '''lymphatics''' that are small and delicate.
[[Image:Portal Triad Histology.jpg|thumb|right|250px|Portal Triad Histology in a Lobule- from [[Gastrointestinal Tract Histology resource|GIT-2 tutorial]] ]]
'''Hepatocytes''' are the smaller liver cells in the lobules. They contain glycogen granules and have a spherical nucleus. They form cords called '''branching plates''' (lamellae). The upper and lower margins are tight junctions. They have 3 functioning surfaces. '''Kupfer macrophages''' are present near the lining of the sinusoids. The hepatocytes stain pink as they are '''eosinophilic'''.
===Acinus===
*the smallest functional unit of the [[Liver - Anatomy & Physiology|liver]] - this unit stresses the dependence of the [[Liver - Anatomy & Physiology|liver]] on its afferent blood vessels and efferent bile ducts
*a roughly diamond shaped parenchymal mass surrounding and supplied by the portal area
*consists of 3 zones:
**Zone 1 - periportal (centroacinar), around the portal areas
**Zone 2 - midzonal
**Zone 3 - centrilobular (periacinar), bordering the hepatic venules
NB: blood enters from Zone 1 to Zone 3 and thus becomes less and less oxygenated
==Links==
'''Click here for information on [[:Category:Liver - Pathology|pathology of the Liver]]'''
'''Click here for information on [[:Category:Liver - Pathology|pathology of the Liver]]'''
'''Click here for information on [[Portosystemic Shunt|portosystemic shunting]]'''
'''Click here for information on [[Portosystemic Shunt|portosystemic shunting]]'''
[http://stream2.rvc.ac.uk/Anatomy/bovine/Pot0061.mp4 Pot 61 The Bovine Liver]
{{Learning
|dragster =[[Comparative Liver Anatomy Dragster resource|Compare liver structure in different species]]
|flashcards = [[Liver - Anatomy & Physiology - Flashcards]]
|videos =[https://wikivet.mediacore.tv/media/bovine-liver-potcast Bovine liver potcast]<br>[https://wikivet.mediacore.tv/media/bovine-liverpng Bovine liver potcast 2]<br>[https://wikivet.mediacore.tv/media/ovine-liver-with-hepatitis-cysticercosa-potcast Ovine liver with hepatitis cysticercosa potcast]<br>[https://wikivet.mediacore.tv/media/equine-liver-with-hydatid-cysts-potcast Equine liver with hydatid cysts potcast]<br>[https://wikivet.mediacore.tv/media/equine-liver-potcast Equine liver potcast]<br>[http://www.onemedicine.tuskegee.edu/DigestiveSystem/Acessory_Organs/Access_Equine.html Liver lobes of the Horse]<br>[http://www.onemedicine.tuskegee.edu/DigestiveSystem/Acessory_Organs/Access_Ruminants.html Liver lobes of the Cow]<br>
|powerpoints = [[Gastrointestinal Tract Histology resource|Histology of the liver - see part 2]]
|Vetstream = [https://www.vetstream.com/canis/Content/Disease/dis01079.asp Acute Liver disease]
}}
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