Difference between revisions of "Liver - Anatomy & Physiology"

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<big><center>[[Alimentary - Anatomy & Physiology|'''BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY''']]</center></big>
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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 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 (hepar) is an extremely important organ in the body of mammals and vertebrates which 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 rather 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 connetion to the gut narrows to become the bile duct. The parenchymal tissue of the liver is formed from proliferating epithelial cords or strands which intergrate 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.
 
The mesoderm of the septum transversum forms the venous sinosoids and connective tissue of the liver.
 +
  
 
==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 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
 +
 
 +
*Passgaes or notches on the median plane allow the caudal vena cava and oesophagus to pass by
 +
 
 +
*The [[Gall Bladder - Anatomy & Physiology|gallbladder]] 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
  
−
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
  
−
==Ligaments==
+
*Right medial
 +
 
 +
*Quadrate
 +
 
 +
*Caudate
 +
 
 +
*Papillary
 +
 
 +
===Ligaments===
 +
 
 +
*Coronary ligament
 +
**Between the liver and disphragm on the diaphragmatic surface of the liver
 +
**Irregular fold of peritoneum
 +
**Surounds the triangular base of the diaphragmayic 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
 +
 
 +
*Triangular ligament
 +
**Right and left sides of the coronary ligament
  
−
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 '''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
 +
 
 +
*Nearly all the blood circulated around the adbomen 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
 +
**Glyconneolysis
 +
**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
 +
**Insulin and glucagon
 +
**Glucocortocoids
 +
**Catecholamines
  
−
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.
+
*Immunoregulation
 +
**Kupfer cells
 +
**Complement synthesis and metabolism
  
−
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.
+
*Storage
 +
**Water soluble vitamins
 +
**fat soluble vitamins
 +
**Iron
 +
**Triglyceride
 +
**Glycogen
  
−
The liver is important in storage of water soluble vitamins, fat soluble vitamins, iron, triglyceride and 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)
  
−
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).
 
  
 
==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)
 +
 
 +
*Larege blood supply
 +
 
 +
*Hepatic artery
 +
 
 +
*Branch of the caeliac artery
  
−
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).
+
*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
  
−
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==
  
−
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.
+
*Effernt 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==
 +
 
 +
[[Image:Lobule Histology.jpg|thumb|right|150px|Liver Lobule Histology - Copyright RVC 2008]]
 +
*Connective tissue capsule around each lobule
 +
 
 +
*Thin mesothelium covers connective tissue layer
 +
 
 +
*The larger liver cells are called lobules
 +
**Each lobule contains an opening for the central vein and contains portal areas
 +
**Lobules composed of liver cords called hepatocytes
 +
**Sinusoids present between hepatocytes containing red blood cells
 +
 
 +
*Portal area present in lobules
 +
**Hepatic artery- thick walls, small diameter
 +
**Hepatic vein- thin walls, large and irregular shape
 +
**Bile ducts- cuboidal or columnar epithelium
 +
**Lymphatics- small and delicate
 +
[[Image:Portal Triad Histology.jpg|thumb|right|150px|Portal Triad Histology in a Lobule- Copyright RVC 2008]]
 +
 
 +
*Hepatocytes are the smaller liver cells in the lobules
 +
**Contain glycogen granules
 +
**Pink stain as are eosinophilic
 +
**Spherical nucleus
 +
**Forms cords called branching plates (lamellae)
 +
**Upper and lower margins are tight junctions
 +
**3 functioning surfaces
 +
***Adjacent to sinusoid contains microvilli
 +
***Between adjacent cells are smooth
 +
***Adjacent cells have short microvilli, membranes diverge, explanded intracellular spaces and bile canaliculi
 +
 
 +
*Kupfer macrophages present near the lining of the sinusoids
 +
 
  
 
==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]]
 +
 
 +
*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]]  
  
−
[[Image:Formation of Bile Acids.jpg|thumb|right|250px|Formation of Bile Acids - Copyright RVC 2008]]
+
*Distal to the cystic duct is the bile duct (ductus choledochus) which transports bile from the 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]]
 
  
 
===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 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
  
−
===Porcine===
+
*No papillary lobe
 +
 
 +
*In the foal the liver liver is larger and more symmetrical
 +
 
 +
*Bile duct opens into the [[Duodenum - Anatomy & Physiology|duodenum]] at the same papillae as the major pancreatic duct
  
−
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.
+
*Bile is constantly secreted
  
−
===Ruminants===
+
===Porcine===
  
−
The liver is entirely displaced to right of the midline. It has fused lobes.
+
*Deep interlobular fissures
  
−
'''Small Ruminants'''
+
*Large amount of interlobular connective tissue
−
Sheep have a deeper umbilical fissure than cows. Sheep also have a smaller caudate lobe than cows and have two papillary processes.
 
  
−
===Avian===
+
*Mottled appearance
  
−
See [[Avian Liver - Anatomy & Physiology|avian liver]]
+
*Deep interlobular fissure divides the lived into 4 lobes- the left, right, medial and lateral
  
−
==Histology==
+
*Small caudate lobe (which does not contact the kidney so no renal impression)
−
[[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.
+
*Mostly on the right of the midline
−
[[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'''.
+
*No papillary lobe
  
 +
===Ruminants===
  
−
===Acinus===
+
*Entirely displaced to right of midline
  
−
*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
+
*Fused lobes
−
*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==
+
'''Small Ruminants'''
 +
*Sheep have a deeper umbilical fissure than cows
  
−
'''Click here for information on [[:Category:Liver - Pathology|pathology of the Liver]]'''
+
*Sheep have a smaller caudate lobe than cows
  
−
'''Click here for information on [[Hepatic Stellate Cells]]'''
+
*Sheep have two papillary processes
  
−
'''Click here for information on [[Bile Formation]]'''
+
===Avian===
  
−
'''Click here for information on [[Portosystemic Shunt|portosystemic shunting]]'''
+
*See [[Avian Liver - Anatomy & Physiology|avian liver]]
  
  
−
{{Learning
+
==Links==
−
|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==
+
[[Liver|Pathology of the Liver]]
−
<rss max="10" highlight="liver hepatopathies diarrhoea">https://www.thewebinarvet.com/gastroenterology-and-nutrition/webinars/feed</rss>
 
  
 +
[http://stream2.rvc.ac.uk/Anatomy/bovine/Pot0061.mp4 Pot 61 The Bovine Liver]
  
−
[[Category:Liver and Gall Bladder - Anatomy & Physiology]]
+
[http://stream2.rvc.ac.uk/Anatomy/equine/pot0228.mp4 Pot 228 The Equine Liver]
−
[[Category:To Do - AimeeHicks]]
 

Revision as of 09:17, 17 July 2008

BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY


Introduction

The liver (hepar) is an extremely important organ in the body of mammals and vertebrates which 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 rather 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 connetion to the gut narrows to become the bile duct. The parenchymal tissue of the liver is formed from proliferating epithelial cords or strands which intergrate 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
  • Passgaes or notches on the median plane allow the caudal vena cava and oesophagus to pass by
  • The gallbladder 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
    • Between the liver and disphragm on the diaphragmatic surface of the liver
    • Irregular fold of peritoneum
    • Surounds the triangular base of the diaphragmayic 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
  • Triangular ligament
    • Right and left sides of the coronary ligament


Function

  • Production of bile
  • Nearly all the blood circulated around the adbomen 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
    • Glyconneolysis
    • 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
    • Insulin and glucagon
    • Glucocortocoids
    • Catecholamines
  • 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)
  • Larege blood supply
  • 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

  • Effernt 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

Liver Lobule Histology - Copyright RVC 2008
  • Connective tissue capsule around each lobule
  • Thin mesothelium covers connective tissue layer
  • The larger liver cells are called lobules
    • Each lobule contains an opening for the central vein and contains portal areas
    • Lobules composed of liver cords called hepatocytes
    • Sinusoids present between hepatocytes containing red blood cells
  • Portal area present in lobules
    • Hepatic artery- thick walls, small diameter
    • Hepatic vein- thin walls, large and irregular shape
    • Bile ducts- cuboidal or columnar epithelium
    • Lymphatics- small and delicate
Portal Triad Histology in a Lobule- Copyright RVC 2008
  • Hepatocytes are the smaller liver cells in the lobules
    • Contain glycogen granules
    • Pink stain as are eosinophilic
    • Spherical nucleus
    • Forms cords called branching plates (lamellae)
    • Upper and lower margins are tight junctions
    • 3 functioning surfaces
      • Adjacent to sinusoid contains microvilli
      • Between adjacent cells are smooth
      • Adjacent cells have short microvilli, membranes diverge, explanded intracellular spaces and bile canaliculi
  • Kupfer macrophages present near the lining of the sinusoids


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

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 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

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


Links

Pathology of the Liver

Pot 61 The Bovine Liver

Pot 228 The Equine Liver

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