The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion. The liver is necessary for survival; there is currently no way to compensate for the absence of liver function.
This organ plays a major role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production, and detoxification. It lies below the diaphragm in the thoracic region of the abdomen. It produces bile, an alkaline compound which aids in digestion, via the emulsification of lipids. It also performs and regulates a wide variety of high-volume biochemical reactions requiring highly specialized tissues, including the synthesis and breakdown of small and complex molecules, many of which are necessary for normal vital function.
I – Anatomy of the liver
An adult human liver normally weighs between 1.4–1.6 kg (3.1–3.5 lb), and is a soft, pinkish-brown, triangular organ. It is both the largest internal organ (the skin being the largest organ overall) and the largest gland in the human body.
It is located in the right upper quadrant of the abdominal cavity, resting just below the diaphragm. The liver lies to the right of the stomach and overlies the gallbladder.
1 ) Blood flow
The liver receives a dual blood supply from the hepatic portal vein and hepatic arteries. Supplying approximately 75% of the liver’s blood supply, the hepatic portal vein carries venous blood drained from the spleen, gastrointestinal tract, and its associated organs. The hepatic arteries supply arterial blood to the liver, accounting for the remainder of its blood flow. Oxygen is provided from both sources; approximately half of the liver’s oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries.
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Blood flows through the sinusoids and empties into the central vein of each lobule. The central veins coalesce into hepatic veins, which leave the liver and empty into the inferior vena cava.
2 ) Biliary flow
The term biliary tree is derived from the arboreal branches of the bile ducts. The bile produced in the liver is collected in bile canaliculi, which merge to form bile ducts. Within the liver, these ducts are called intrahepatic (within the liver) bile ducts, and once they exit the liver they are considered extrahepatic (outside the liver).
The intrahepatic ducts eventually drain into the right and left hepatic ducts, which merge to form the common hepatic duct. The cystic duct from the gallbladder joins with the common hepatic duct to form the common bile duct.
Bile can either drain directly into the duodenum via the common bile duct or be temporarily stored in the gallbladder via the cystic duct. The common bile duct and the pancreatic duct enter the second part of the duodenum together at the ampulla of Vater.
3 ) Surface anatomy
A ) Peritoneal ligaments
Apart from a patch where it connects to the diaphragm (the so-called “bare area”), the liver is covered entirely by visceral peritoneum, a thin, double-layered membrane that reduces friction against other organs. The peritoneum folds back on itself to form the falciform ligament and the right and left triangular ligaments.
... ducts. The right hepatic duct drains the right lobe of the liver and the left duct drains the left lobe, caudate lobe, and quadrate lobe. Hepatic Ducts The right and left hepatic ducts ... the cystic duct from the gallbladder to form the common bile duct. Bile Duct The bile duct (common bile duct) is about ... of the stomach Peritoneal Ligaments of the Liver The falciform ligament, which is a two-layered ...
These “ligaments” are in no way related to the true anatomic ligaments in joints, and have essentially no functional importance, but they are easily recognizable surface landmarks. An exception to this is the falciform ligament, which attaches the liver to the posterior portion of the anterior body wall.
B ) Lobes
Traditional gross anatomy divided the liver into four lobes based on surface features. The falciform ligament is visible on the front (anterior side) of the liver. This divides the liver into a left anatomical lobe, and a right anatomical lobe.
If the liver flipped over, to look at it from behind (the visceral surface), there are two additional lobes between the right and left. These are the caudate lobe (the more superior), and below this the quadrate lobe.
From behind, the lobes are divided up by the ligamentum venosum and ligamentum teres (anything left of these is the left lobe), the transverse fissure (or porta hepatis) divides the caudate from the quadrate lobe, and the right sagittal fossa, which the inferior vena cava runs over, separates these two lobes from the right lobe.
Each of the lobes is made up of lobules; a vein goes from the centre of each lobule which then joins to the hepatic vein to carry blood out from the liver.
On the surface of the lobules there are ducts, veins and arteries that carry fluids to and from them.
II – Physiology of the liver
The various functions of the liver are carried out by the liver cells or hepatocytes. Currently, there is no artificial organ or device capable of emulating all the functions of the liver. Some functions can be emulated by liver dialysis, an experimental treatment for liver failure.
1 ) Synthesis
Further information: Proteins produced and secreted by the liver
• A large part of amino acid synthesis
• The liver performs several roles in carbohydrate metabolism:
o Gluconeogenesis (the synthesis of glucose from certain amino acids, lactate or glycerol)
o Glycogenolysis (the breakdown of glycogen into glucose)
o Glycogenesis (the formation of glycogen from glucose)(muscle tissues can also do this)
RNA splicing is a process in which certain parts, called introns, of an RNA molecule are cut out to create a desired RNA strand made out of exons, the parts of the RNA molecule that remain and are expressed. As a pre-mRNA molecule is guided through a spliceosome, small nuclear ribonucleoprotiens (snRNPs) find the areas where the pre-mRNA’s introns should be cut out. Since the pre-mRNA can be ...
• The liver is responsible for the mainstay of protein metabolism, synthesis as well as degradation
• The liver also performs several roles in lipid metabolism:
o Cholesterol synthesis
o Lipogenesis, the production of triglycerides (fats).
• The liver produces coagulation factors I (fibrinogen), II (prothrombin), V, VII, IX, X and XI, as well as protein C, protein S and antithrombin.
• In the first trimester fetus, the liver is the main site of red blood cell production. By the 32nd week of gestation, the bone marrow has almost completely taken over that task.
• The liver produces and excretes bile (a greenish liquid) required for emulsifying fats. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder.
• The liver also produces insulin-like growth factor 1 (IGF-1), a polypeptide protein hormone that plays an important role in childhood growth and continues to have anabolic effects in adults.
• The liver is a major site of thrombopoietin production. Thrombopoietin is a glycoprotein hormone that regulates the production of platelets by the bone marrow.
2 ) Breakdown
• The breakdown of insulin and other hormones
• The liver breaks down hemoglobin, creating metabolites that are added to bile as pigment (bilirubin and biliverdin).
• The liver breaks down or modifies toxic substances (e.g., methylation) and most medicinal products in a process called drug metabolism. This sometimes results in toxication, when the metabolite is more toxic than its precursor. Preferably, the toxins are conjugated to avail excretion in bile or urine.
• The liver converts ammonia to urea.
3 ) Other functions
• The liver stores a multitude of substances, including glucose (in the form of glycogen), vitamin A (1–2 years’ supply), vitamin D (1–4 months’ supply), vitamin B12, iron, and copper.
• The liver is responsible for immunological effects- the reticuloendothelial system of the liver contains many immunologically active cells, acting as a ‘sieve’ for antigens carried to it via the portal system.
• The liver produces albumin, the major osmolar component of blood serum.
Proteins are made up of long chains of amino acids, just a chain of ami. tacids makes up the primary structure. The secondary structure is formed by hydrogen bonds joining the chains in certain places to make an alpha helix or a beta sheet. The tertiary structure is formed by even more folding and joining of the chains to make a globular mass or fibrous mass. An example of this would be a carrier ...
• The liver synthesizes angiotensinogen, a hormone that is responsible for raising the blood pressure when activated by renin, an enzyme that is released when the kidney senses low blood pressure.