Difference between revisions of "Liver - Anatomy & Physiology"

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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 atrophies 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 atropies 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.
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==Structure==
 
==Structure==
  
−
[[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|150px|Topography of the Liver (Dog)- Copyright RVC 2008]]
 +
*Cranial part of the abdomen
 +
 
 +
*Immediately caudal to the diaphragm
 +
 
 +
*Cranial to the [[Monogastric Stomach - Anatomy & Physiology|stomach]] and intestines
 +
 
 +
*Generally the bulk of the liver on the right of the midline
 +
 
 +
*Divided into lobes by fissures
 +
 
 +
*Cranially the liver is convex, called the diaphragmatic surface
 +
 
 +
*Caudally the liver is concave, called the visceral surface
 +
 
 +
*Caudate lobe has a renal impression from the right [[Urinary System - Anatomy & Physiology#Upper Urinary Tract|kidney]]
 +
 
 +
*Gastric impression occupies the whole of the left half of the visceral face
 +
 
 +
*[[Duodenum - Anatomy & Physiology|Duodenal]] impression at the junction of the right and quadrate lobes continuing 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
 +
 
 +
*Lesser omentum (often fat filled) on the visceral surface between the left lateral lobe, heptic porta and lesser curvature of the [[Monogastric Stomach - Anatomy & Physiology|stomach]]
 +
 
 +
*Oesophageal notch where [[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==
+
*Lobes
  
−
The liver can be divided into lobes, lobules, hepatocytes and sinusoids.
+
*Lobules
 +
 
 +
*Hepatocytes and sinusoids
  
 
===Lobes of the Liver===
 
===Lobes of the Liver===
  
−
The lobes of the liver include the left lateral, left medial, right lateral, right medial, quadrate, caudate and papillary.
+
*Left lateral
 +
 
 +
*Left medial
 +
 
 +
*Right lateral
 +
 
 +
*Right medial
 +
 
 +
*Quadrate
 +
 
 +
*Caudate
 +
 
 +
*Papillary
 +
 
 +
===Ligaments===
 +
 
 +
*Coronary ligament
 +
**Attaches the liver (from the diaphragmatic surface) to the diaphragm
 +
**Irregular fold of peritoneum
 +
**Surounds the triangular base of the diaphragmatic surface
 +
**Continuous with outer most layer of the caudal vena cava
  
−
==Ligaments==
+
*Falciform ligament
 +
**Ventral to the coronary ligament
 +
**Fat filled embryological remnant of the fetal blood vessels from the placenta
 +
**Causes problems for surgical entry into the abdomen
 +
**Located cranial to the umbilicus
 +
**Vestige of the umbilical vein
  
−
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.
+
*Triangular ligament
−
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.
+
**Right and left sides of the coronary ligament
−
The '''triangular ligament''' is on the right and left sides of the coronary ligament.
 
  
 
==Function==
 
==Function==
  
−
Production of bile see <big>'''[[Bile Formation]]'''</big>.
+
*Production of bile see <big>'''[[Bile Formation]]'''</big>
 +
 
 +
*Nearly all the blood circulated around the abdomen flows back through the portal vein to the liver where it comes in contact with the liver cells, ensuring the products of digestion are presented to the hepatic cells before entering the general circulation.
 +
 
 +
*Carbohydrate metabolism
 +
**Glycogenesis
 +
**Glyconeolysis
 +
**Gluconeogenesis
 +
**Breakdown of insulin and other [[Hormones - Anatomy & Physiology|hormones]]
 +
 
 +
*Protein metabolism
 +
**Produces soluble mediators of the clotting cascade
 +
**Albumin
 +
**Hormone transporting globulins
 +
 
 +
*Lipid metabolism
 +
**Lipogenesis
 +
**Synthesis of cholesterol
 +
 
 +
*Hormonal control
 +
**Insulin and glucagon
 +
**Glucocortocoids
 +
**Catecholamines
 +
**Synthesises other important [[Hormones - Anatomy & Physiology|hormones]] (see [[Liver Endocrine Function - Anatomy & Physiology|Endocrine System]])
 +
 
 +
*Immunoregulation
 +
**Kupfer cells
 +
**Complement synthesis and metabolism
  
−
Nearly all the blood circulated around the abdomen flows back through the portal vein to the liver where it comes in contact with the liver cells, ensuring the products of digestion are presented to the hepatic cells before entering the general circulation. Other functions include carbohydrate metabolism, glycogenesis, glyconeolysis, gluconeogenesis and the breakdown of insulin and other [[Hormones - Anatomy & Physiology|hormones]]. Protein metabolism produces soluble mediators of the clotting cascade, Albumin and hormone transporting globulins. The liver is also involved in lipid metabolism, lipogenesis and the synthesis of cholesterol.
+
*Storage
 +
**Water soluble vitamins
 +
**fat soluble vitamins
 +
**Iron
 +
**Triglyceride
 +
**Glycogen
  
−
The liver has a role in hormonal control of the following; Insulin and glucagon, Glucocortocoids, Catecholamines and the synthesis of other important [[Hormones - Anatomy & Physiology|hormones]] (see [[Liver Endocrine Function - Anatomy & Physiology|Endocrine System]]). It also has a role in immunoregulation via kupfer cells and the complement synthesis and metabolism.
+
*Breaks down haemoglobin
  
−
The liver is important in storage of water soluble vitamins, fat soluble vitamins, iron, triglyceride and glycogen.
+
*Breaks down toxic substances through drug metabolism
  
−
The liver breaks down haemoglobin and toxic substances through drug metabolism. It converts ammonia to urea and allows the management of endogenous waste, e.g haem (Hb, cytochromes, Mb) and ammonia (amino acids).
+
*Converts ammonia to urea
 +
 
 +
*Management of endogenous waste, e.g haem (Hb, cytochromes, Mb) and ammonia (amino acids)
  
 
==Vasculature==
 
==Vasculature==
  
−
[[Image:Blood Flow In and Away from the Liver.jpg|thumb|right|250px|Blood Flow in the Liver - Copyright nabrown RVC 2008]]
+
[[Image:Blood Flow In and Away from the Liver.jpg|thumb|right|150px|Blood Flow in the Liver - Copyright nabrown RVC 2008]]
 +
*Dual blood supply
 +
**70-80% hepatic portal vein (nutrient rich)
 +
**20-30% hepatic artery (oxygen rich)
 +
 
 +
*Large blood supply (nearly a 1/3 of cardiac output passes through the liver)
 +
 
 +
*Hepatic artery
 +
 
 +
*Branch of the caeliac artery
 +
 
 +
*Portal vein
 +
**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
 +
 
 +
*Central vein 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
  
−
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).
+
*Blood from the central vein open into the caudal vena cava
  
−
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.
+
*Liver circulation controlled by interarterial, intervenous and arteriovenous, by sphincter mechanisms allowing carefull reglulation
  
 
==Innervation==
 
==Innervation==
  
−
The liver is innervated by sympathetic nerves from the '''periarterial plexuses''' and '''parasympathetic nerves''' from the vagal trunk.
+
*Sympathetic nerves from periarterial plexuses
 +
 
 +
*Parasympathetic nerves from vagal trunk
  
 
==Lymphatics==
 
==Lymphatics==
  
−
Efferent vessels pass to hepatic nodes around the hepatic porta. The lymph drains into the visceral cysterna chyli. Some lymph travels to the accessory hepatic and caudal mediastinal lymph nodes on the caudal vena cava.
+
*Efferent vessels pass to hepatic nodes around the hepatic porta
 +
 
 +
*The lymph drains into the visceral cysterna chyli
 +
 
 +
*Some lymph travels to the accessory hepatic and caudal mediastinal lymph nodes on the caudal vena cava
 +
 
 +
==[[Liver - Histology|Histology]]==
  
 
==Hepatic Duct Systems==
 
==Hepatic Duct Systems==
  
−
There are '''canaliculi''' within lobules. Canaliculi open into larger ductules then into a few large hapatic ducts. Before and shortly after leaving the hepatic porta, the ducts combine into a single trunk which runs to the [[Duodenum - Anatomy & Physiology|duodenum]]. The cystic duct runs from common trunk to the [[Gall Bladder - Anatomy & Physiology|gall bladder]] transporting bile from the liver to the [[Gall Bladder - Anatomy & Physiology|gall bladder]]. Distal to the cystic duct is the bile duct (ductus choledochus) which transports bile from the [[Gall Bladder - Anatomy & Physiology|gall bladder]] into the [[Duodenum - Anatomy & Physiology|duodenum]]. There are no valves, so bile may flow in either direction.
+
*Canaliculi within lobules
 +
 
 +
*Canaliculi opein into larger ductules then into a few large hapatic ducts
 +
 
 +
*Before and shortly after leaving the hepatic porta the ducts combine into a single trunk which runs to the [[Duodenum - Anatomy & Physiology|duodenum]]
  
−
[[Image:Formation of Bile Acids.jpg|thumb|right|250px|Formation of Bile Acids - Copyright RVC 2008]]
+
*The cystic duct runs from common trunk to the [[Gall Bladder - Anatomy & Physiology|gall bladder]] transporting bile from the liver to the [[Gall Bladder - Anatomy & Physiology|gall bladder]]
 +
 
 +
*Distal to the cystic duct is the bile duct (ductus choledochus) which transports bile from the [[Gall Bladder - Anatomy & Physiology|gall bladder]] into the [[Duodenum - Anatomy & Physiology|duodenum]]
 +
 
 +
*No valves so bile may flow in either direction
 +
 
 +
[[Image:Formation of Bile Acids.jpg|thumb|right|150px|Formation of Bile Acids - Copyright RVC 2008]]
  
 
==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.  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.
+
*Composed of cholesterol, bile acids and steroids
 +
 
 +
*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
 +
 
 +
*Emulsify fats
 +
 
 +
*Helps absorb fat soluble vitamins
 +
 
 +
*In aqueous solution 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|150px|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 Overview - Anatomy & Physiology#Upper Urinary Tract|kidney]].
+
*Both left and right lobes subdivided
 +
 
 +
*Complete obstruction of the hepatic artery is fatal
 +
 
 +
*Almost entirely intra-thoracic
 +
 
 +
*Enlarged caudate process contacts right [[Urinary System - Anatomy & Physiology#Upper Urinary Tract|kidney]]
  
 
===Equine===
 
===Equine===
  
−
The liver is contained entirely within the rib cage, to the right of the midline. It is less lobated. There is no [[Gall Bladder - Anatomy & Physiology|gall bladder]] and the left lobe is subdivided. There is no papillary lobe. In the foal, the liver is larger and more symmetrical. The bile duct opens into the [[Duodenum - Anatomy & Physiology|duodenum]] at the same papillae as the major pancreatic duct. Bile is constantly secreted.
+
*Contained entirely within the rib cage
−
[[Image:Pig Liver Topography.jpg|thumb|right|250px|Liver Topography (Pig) - Copyright Nottingham 2008]]
+
 
 +
*To the right of the midline
 +
 
 +
*Less lobated
 +
 
 +
*No [[Gall Bladder - Anatomy & Physiology|gall bladder]]
 +
 
 +
*Left lobe subdivided
 +
 
 +
*No papillary lobe
 +
 
 +
*In the foal the liver is larger and more symmetrical
 +
 
 +
*Bile duct opens into the [[Duodenum - Anatomy & Physiology|duodenum]] at the same papillae as the major pancreatic duct
 +
 
 +
*Bile is constantly secreted
 +
[[Image:Pig Liver Topography.jpg|thumb|right|150px|Liver Topography (Pig) - Copyright Nottingham 2008]]
  
 
===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 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.
+
*Deep interlobular fissures
 +
 
 +
*Large amount of interlobular connective tissue
 +
 
 +
*Mottled appearance
 +
 
 +
*Deep interlobular fissure divides the lived into 4 lobes- the left, right, medial and lateral
 +
 
 +
*Small caudate lobe (which does not contact the [[Urinary System - Anatomy & Physiology#Upper urinary Tract|kidney]] so no renal impression)
 +
 
 +
*Mostly on the right of the midline
 +
 
 +
*No papillary lobe
  
 
===Ruminants===
 
===Ruminants===
  
−
The liver is entirely displaced to right of the midline. It has fused lobes.
+
*Entirely displaced to right of midline
 +
 
 +
*Fused lobes
  
 
'''Small Ruminants'''
 
'''Small Ruminants'''
−
Sheep have a deeper umbilical fissure than cows. Sheep also have a smaller caudate lobe than cows and have two papillary processes.
+
*Sheep have a deeper umbilical fissure than cows
  
−
===Avian===
+
*Sheep have a smaller caudate lobe than cows
  
−
See [[Avian Liver - Anatomy & Physiology|avian liver]]
+
*Sheep have two papillary processes
  
−
==Histology==
+
===Avian===
−
[[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.
+
*See [[Avian Liver - Anatomy & Physiology|avian liver]]
−
[[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'''.
+
==Test yourself with the Liver flashcards==
  
 +
[[Liver - Anatomy & Physiology - Flashcards|Liver & Gall Bladder Flashcards]]
  
−
===Acinus===
+
==Links==
  
−
*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
+
[[:Category:Liver - Pathology|Pathology of the Liver]]
−
*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]]'''
+
[[Hepatic Stellate Cells]]
  
−
'''Click here for information on [[Hepatic Stellate Cells]]'''
+
[[Bile Formation]]
  
−
'''Click here for information on [[Bile Formation]]'''
+
[[Portosystemic Shunt|Portosystemic Shunting]]
  
−
'''Click here for information on [[Portosystemic Shunt|portosystemic shunting]]'''
+
[http://www.onemedicine.tuskegee.edu/DigestiveSystem/Acessory_Organs/Access_Equine.html Liver lobes of the Horse]
  
 +
[http://www.onemedicine.tuskegee.edu/DigestiveSystem/Acessory_Organs/Access_Ruminants.html Liver lobes of the Cow]
  
−
{{Learning
+
[http://stream2.rvc.ac.uk/Anatomy/bovine/Pot0061.mp4 Pot 61 The Bovine Liver]
−
|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]
 
−
}}
 
  
−
==Webinars==
+
[http://stream2.rvc.ac.uk/Anatomy/equine/pot0228.mp4 Pot 228 The Equine Liver]
−
<rss max="10" highlight="liver hepatopathies diarrhoea">https://www.thewebinarvet.com/gastroenterology-and-nutrition/webinars/feed</rss>
 
  
  
 
[[Category:Liver and Gall Bladder - Anatomy & Physiology]]
 
[[Category:Liver and Gall Bladder - Anatomy & Physiology]]
−
[[Category:To Do - AimeeHicks]]
 

Revision as of 13:30, 8 September 2010

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 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 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 mesoderm of the septum transversum forms the venous sinosoids and connective tissue of the liver.

Structure

Topography of the Liver (Dog)- Copyright RVC 2008
  • Cranial part of the abdomen
  • Immediately caudal to the diaphragm
  • Cranial to the stomach and intestines
  • Generally the bulk of the liver on the right of the midline
  • Divided into lobes by fissures
  • Cranially the liver is convex, called the diaphragmatic surface
  • Caudally the liver is concave, called the visceral surface
  • Caudate lobe has a renal impression from the right kidney
  • Gastric impression occupies the whole of the left half of the visceral face
  • Duodenal impression at the junction of the right and quadrate lobes continuing onto the right lateral and caudate lobes
  • Passages or notches on the median plane allow the caudal vena cava and oesophagus to pass by
  • The 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
  • Lesser omentum (often fat filled) on the visceral surface between the left lateral lobe, heptic porta and lesser curvature of the stomach
  • Oesophageal notch where oesophagus passes over the liver

Divisions of the Liver

  • Lobes
  • Lobules
  • Hepatocytes and sinusoids

Lobes of the Liver

  • Left lateral
  • Left medial
  • Right lateral
  • Right medial
  • Quadrate
  • Caudate
  • Papillary

Ligaments

  • Coronary ligament
    • Attaches the liver (from the diaphragmatic surface) to the diaphragm
    • Irregular fold of peritoneum
    • Surounds the triangular base of the diaphragmatic surface
    • Continuous with outer most layer of the caudal vena cava
  • Falciform ligament
    • Ventral to the coronary ligament
    • Fat filled embryological remnant of the fetal blood vessels from the placenta
    • Causes problems for surgical entry into the abdomen
    • Located cranial to the umbilicus
    • Vestige of the umbilical vein
  • Triangular ligament
    • Right and left sides of the coronary ligament

Function

  • Nearly all the blood circulated around the abdomen flows back through the portal vein to the liver where it comes in contact with the liver cells, ensuring the products of digestion are presented to the hepatic cells before entering the general circulation.
  • Carbohydrate metabolism
    • Glycogenesis
    • Glyconeolysis
    • Gluconeogenesis
    • Breakdown of insulin and other hormones
  • Protein metabolism
    • Produces soluble mediators of the clotting cascade
    • Albumin
    • Hormone transporting globulins
  • Lipid metabolism
    • Lipogenesis
    • Synthesis of cholesterol
  • Hormonal control
  • Immunoregulation
    • Kupfer cells
    • Complement synthesis and metabolism
  • Storage
    • Water soluble vitamins
    • fat soluble vitamins
    • Iron
    • Triglyceride
    • Glycogen
  • Breaks down haemoglobin
  • Breaks down toxic substances through drug metabolism
  • Converts ammonia to urea
  • Management of endogenous waste, e.g haem (Hb, cytochromes, Mb) and ammonia (amino acids)

Vasculature

Blood Flow in the Liver - Copyright nabrown RVC 2008
  • Dual blood supply
    • 70-80% hepatic portal vein (nutrient rich)
    • 20-30% hepatic artery (oxygen rich)
  • Large blood supply (nearly a 1/3 of cardiac output passes through the liver)
  • Hepatic artery
  • Branch of the caeliac artery
  • Portal vein
    • 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
  • Central vein 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 open into the caudal vena cava
  • Liver circulation controlled by interarterial, intervenous and arteriovenous, by sphincter mechanisms allowing carefull reglulation

Innervation

  • Sympathetic nerves from periarterial plexuses
  • Parasympathetic nerves from vagal trunk

Lymphatics

  • Efferent vessels pass to hepatic nodes around the hepatic porta
  • The lymph drains into the visceral cysterna chyli
  • Some lymph travels to the accessory hepatic and caudal mediastinal lymph nodes on the caudal vena cava

Histology

Hepatic Duct Systems

  • Canaliculi within lobules
  • Canaliculi opein into larger ductules then into a few large hapatic ducts
  • Before and shortly after leaving the hepatic porta the ducts combine into a single trunk which runs to the duodenum
  • Distal to the cystic duct is the bile duct (ductus choledochus) which transports bile from the gall bladder into the duodenum
  • No valves so bile may flow in either direction
Formation of Bile Acids - Copyright RVC 2008

Bile Acids

  • Composed of cholesterol, bile acids and steroids
  • 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
  • Emulsify fats
  • Helps absorb fat soluble vitamins
  • In aqueous solution form micelles which are amphiphilic and can transport free fatty acids across the brush border

Species Differences

Liver Topography (Dog) - Copyright Nottingham 2008

Canine & Feline

  • Both left and right lobes subdivided
  • Complete obstruction of the hepatic artery is fatal
  • Almost entirely intra-thoracic
  • Enlarged caudate process contacts right kidney

Equine

  • Contained entirely within the rib cage
  • To the right of the midline
  • Less lobated
  • Left lobe subdivided
  • No papillary lobe
  • In the foal the liver is larger and more symmetrical
  • Bile duct opens into the duodenum at the same papillae as the major pancreatic duct
  • Bile is constantly secreted
Liver Topography (Pig) - Copyright Nottingham 2008

Porcine

  • Deep interlobular fissures
  • Large amount of interlobular connective tissue
  • Mottled appearance
  • Deep interlobular fissure divides the lived into 4 lobes- the left, right, medial and lateral
  • Small caudate lobe (which does not contact the kidney so no renal impression)
  • Mostly on the right of the midline
  • No papillary lobe

Ruminants

  • Entirely displaced to right of midline
  • Fused lobes

Small Ruminants

  • Sheep have a deeper umbilical fissure than cows
  • Sheep have a smaller caudate lobe than cows
  • Sheep have two papillary processes

Avian

Test yourself with the Liver flashcards

Liver & Gall Bladder Flashcards

Links

Pathology of the Liver

Hepatic Stellate Cells

Bile Formation

Portosystemic Shunting

Liver lobes of the Horse

Liver lobes of the Cow

Pot 61 The Bovine Liver

Pot 228 The Equine Liver

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