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Liver - Anatomy & Physiology (view source)
Revision as of 11:35, 14 September 2010
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==Structure==
==Structure==
[[Image:Topography of the Liver.jpg|thumb|right|150px|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.
==Divisions of the Liver==
The liver can be divided into lobes, 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.
==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 '''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>.
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.
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.
The liver is important in storage of water soluble vitamins, fat soluble vitamins, iron, triglyceride and glycogen.
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|150px|Blood Flow in the Liver - Copyright nabrown RVC 2008]]
[[Image:Blood Flow In and Away from the Liver.jpg|thumb|right|250px|Blood Flow in the Liver - Copyright nabrown RVC 2008]]
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.
==Innervation==
==Innervation==
The liver is innervated by sympathetic nerves from the '''periarterial plexuses''' and '''parasympathetic nerves''' from the 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.
==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.
[[Image:Formation of Bile Acids.jpg|thumb|right|250px|Formation of Bile Acids - Copyright RVC 2008]]
[[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. 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.
==Species Differences==
==Species Differences==
[[Image:Canine Liver Topography.jpg|thumb|right|150px|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]].
===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.
[[Image:Pig Liver Topography.jpg|thumb|right|250px|Liver Topography (Pig) - Copyright Nottingham 2008]]
[[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 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.
===Ruminants===
===Ruminants===
The liver is entirely displaced to right of the midline. It has 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.
===Avian===
See [[Avian Liver - Anatomy & Physiology|avian liver]]
===Avian===
==Links==
'''Test yourself with the [[Liver - Anatomy & Physiology - Flashcards|Liver & Gall Bladder Flashcards]]'''
[[Liver - Anatomy & Physiology - Flashcards|Liver & Gall Bladder Flashcards]]
'''Click here for information on [[Liver - Histology|liver histology]]'''
'''Click here for information on [[:Category:Liver - Pathology|pathology of the Liver]]'''
[[:Category:Liver - Pathology|Pathology of the Liver]]
'''Click here for information on [[Hepatic Stellate Cells]]'''
[[Hepatic Stellate Cells]]
'''Click here for information on [[Bile Formation]]'''
[[Bile Formation]]
'''Click here for information on [[Portosystemic Shunt|portosystemic shunting]]'''
'''Video links:'''
[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_Equine.html Liver lobes of the Horse]
[[Category:Liver and Gall Bladder - Anatomy & Physiology]]
[[Category:Liver and Gall Bladder - Anatomy & Physiology]]
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[[Category:To Do - AimeeHicks]]