Liver Totally Explained

Everything about Hepatic totally explained

The liver is the largest visceral organ in the human body, and is an organ present in vertebrates and some other animals. It 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, and detoxification. The liver is also the largest gland in the human body. 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 very specialized tissues.
Medical terms related to the liver often start in hepato- or hepatic from the Greek word for liver, hēpar (ήπαρ).

Anatomy

The adult human liver normally weighs between 1.4 - 1.6 kilograms (3.1 - 3.5 pounds), and it's a soft, pinkish-brown, triangular organ. Averaging about the size of an American football in adults, it's both the largest internal organ and the largest gland in the human body.
It is located on the right side of the upper abdomen below the diaphragm anatomy. The liver lies to the right of the stomach and overlies the gallbladder.

Flow of blood

The splenic vein joins the inferior mesenteric vein, which then together join the superior mesenteric vein to form the hepatic portal vein, bringing venous blood from the spleen, pancreas, stomach, small intestine, and large intestine, so that the liver can process the nutrients and biproducts of food digestion.
The hepatic veins of the blood can be from other branches such as the superior mesenteric artery.
Both the portal venules & the hepatic arterioles enter approximately one million identical lobules acini, likened to and changes in the size of chylomicrons lipoproteins of dietary origin brought about by the quantity & types of food fats.
Approximately 60.5% to 80% of the blood flow to the liver is from the portal venous system, and 1/4 is from the hepatic artery.

Flow of bile

The bile produced in the liver is collected in bile canaliculi, which merge to form bile ducts.
   These eventually drain into the right and left hepatic ducts, which in turn 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 duodenum together at the ampulla of Vater.
   The branchings of the bile ducts resemble those of a tree, and indeed the term "biliary tree" is commonly used in this setting.

Regeneration

The liver is among the few internal human organs capable of natural regeneration of lost tissue; as little as 25% of remaining liver can regenerate into a whole liver again.
This is predominantly due to the hepatocytes acting as unipotential stem cells (for example a single hepatocyte can divide into two hepatocyte daughter cells). There is also some evidence of bipotential stem cells, called ovalocyte (o´və-lo-sīt), which exist in the Canals of Hering. These cells can differentiate into either hepatocytes or cholangiocytes (cells that line the bile ducts).

Traditional (Surface) anatomy

Peritoneal ligaments

Apart from a patch where it connects to the diaphragm, 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.
These "ligaments" are in no way related to the true anatomic ligaments in joints, and have essentially no functional importance, but they're easily recognizable surface landmarks.

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.

Modern (Functional) anatomy

The central area where the common bile duct, hepatic portal vein, and hepatic artery enter is the hilum or "porta hepatis". The duct, vein, and artery divide into left and right branches, and the portions of the liver supplied by these branches constitute the functional left and right lobes.
The liver performs over 500 jobs, and produces over 1,000 essential enzymes.
The functional lobes are separated by a plane joining the gallbladder fossa to the inferior vena cava. This separates the liver into the true right and left lobes. The middle hepatic vein also demarcates the true right and left lobes. The right lobe is further divided into an anterior and posterior segment by the right hepatic vein. The left lobe is divided into the medial and lateral segments by the left hepatic vein. The fissure for the ligamentum teres (the ligamentum teres becomes the falciform ligament) also separates the medial and lateral segments. The medial segment is what used to be called the quadrate lobe. In the widely used Couinaud or "French" system, the functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein. The caudate lobe is a separate structure which receives blood flow from both the right- and left-sided vascular branches. The subsegments corresponding to the anatomical lobes are as follows:

Segment*	Couinaud segments
Caudate	1
Lateral	2, 3
Medial	4a, 4b
Right	5, 6, 7, 8

or lobe in the Caudate's case. Each number in the list corresponds to one in the table.
1. Caudate
2. Superior subsegment of the lateral segment
3. Inferior subsegment of the lateral segment
4. 1. Superior subsegment of the medial segment
  2. Inferior subsegment of the medial segment
5. Inferior subsegment of the anterior segment
6. Inferior subsegment of the posterior segment
7. Superior subsegment of the posterior segment
8. Superior subsegment of the anterior segment

Physiology

The various functions of the liver are carried out by the liver cells or hepatocytes.

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 performs several roles in carbohydrate metabolism:

Gluconeogenesis (the synthesis of glucose from certain amino acids, lactate or glycerol)
Glycogenolysis (the breakdown of glycogen into glucose) (muscle tissues can also do this)
Glycogenesis (the formation of glycogen from glucose)
The breakdown of insulin and other hormones

The liver is responsible for the mainstay of protein metabolism. For instance, the liver can convert lactic acid to alanine.

The liver also performs several roles in lipid metabolism:

Cholesterol synthesis
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.

The liver breaks down haemoglobin, creating metabolites that are added to bile as pigment (bilirubin and biliverdin).

The liver breaks down toxic substances and most medicinal products in a process called drug metabolism. This sometimes results in toxication, when the metabolite is more toxic than its precursor.

The liver converts ammonia to urea.

The liver stores a multitude of substances, including glucose (in the form of glycogen), vitamin B12, iron, and copper.

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 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. Currently, there's 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.

Diseases of the liver

Many diseases of the liver are accompanied by jaundice caused by increased levels of bilirubin in the system. The bilirubin results from the breakup of the hemoglobin of dead red blood cells; normally, the liver removes bilirubin from the blood and excretes it through bile.

Hepatitis, inflammation of the liver, caused mainly by various viruses but also by some poisons, autoimmunity or hereditary conditions.

Cirrhosis is the formation of fibrous tissue in the liver, replacing dead liver cells. The death of the liver cells can for example be caused by viral hepatitis, alcoholism or contact with other liver-toxic chemicals.

Haemochromatosis, a hereditary disease causing the accumulation of iron in the body, eventually leading to liver damage.

Cancer of the liver (primary hepatocellular carcinoma or cholangiocarcinoma and metastatic cancers, usually from other parts of the gastrointestinal tract).

Wilson's disease, a hereditary disease which causes the body to retain copper.

Primary sclerosing cholangitis, an inflammatory disease of the bile duct, likely autoimmune in nature.

Primary biliary cirrhosis, autoimmune disease of small bile ducts.

Budd-Chiari syndrome, obstruction of the hepatic vein.

Gilbert's syndrome, a genetic disorder of bilirubin metabolism, found in about 5% of the population.

Glycogen storage disease type II,The build-up of glycogen causes progressive muscle weakness (myopathy) throughout the body and affects various body tissues, particularly in the heart, skeletal muscles, liver and nervous system. There are also many pediatric liver disease, including biliary atresia, alpha-1 antitrypsin deficiency, alagille syndrome, and progressive familial intrahepatic cholestasis, to name but a few.
A number of liver function tests are available to test the proper function of the liver. These test for the presence of enzymes in blood that are normally most abundant in liver tissue, metabolites or products.

Symptoms of a diseased liver

The external signs include a coated tongue, bad breath, skin rashes, itchy skin, excessive sweating, offensive body odour, dark circles under the eyes, red swollen and itchy eyes, acne rosacea, brownish spots and blemishes on the skin, flushed facial appearance or excessive facial blood vessels. Other symptoms include jaundice, dark urine, pale stool, bone loss, easy bleeding, itching, small, spider-like blood vessels visible in the skin, enlarged spleen, fluid in the abdominal cavity, chills, pain from the biliary tract or pancrea, and an enlarged gallbladder.
   The symptoms related to liver dysfunction include both physical signs and a variety of symptoms related to digestive problems, blood sugar problems, immune disorders, abnormal absorption of fats, and metabolism problems.
   The malabsorption of fats may lead to symptoms that include indigestion, reflux, hemmorhoids, gall stones, intolerance to fatty foods, intolerance to alcohol, nausea and vomiting attacks, abdominal bloating, and constipation.
   Nervous system disorders include depression, mood changes, especially anger and irritability, poor concentration and "foggy brain", overheating of the body, especially the face and torso, and recurrent headaches (including migraine) associated with nausea.
   The blood sugar problems include a craving for sugar, hypoglycaemia and unstable blood sugar levels, and the onset of diabetes (Type 2).
   Abnormalities in the level of fats in the blood stream include elevated LDL cholesterol, reduced HDL cholesterol, elevated triglycerides, clogged arteries leading to high blood pressure heart attacks and strokes, build up of fat in other body organs (fatty degeneration of organs), lumps of fat in the skin (lipomas and other fatty tumors), excessive weight gain (which may lead to obesity), inability to lose weight even while dieting, sluggish metabolism, protuberant abdomen (pot belly), cellulite, fatty liver, and a roll of fat around the upper abdomen (liver roll).
   The College of Holistic Medicine lists other symptoms of a diseased liver that include tired eyes, a tendency to have accidents, weak sexual vitality, impotence and prostate problems, a psychologically that you're irritable and get angry easily, devoting far too much attention to trivial details, overeating, stubborness, prone to anger, highly emotional and hypersensitive, heaviness in the head, poor digestion, hemorrhoids, ovarian problems and cysts, PMS, flatulence and petrifaction of tissues, and possible headaches and migraines.

Herbal Treatments

The most commonly used herbs for liver problems include Milk Thistle, Dandelion Root, Licorice Root, and Chicory root. Milk Thistle is the best studied herb for hepatitis, and has shown to help protect and regenerate liver cells.

Liver transplantation

Human liver transplant was first performed by Thomas Starzl in USA and Roy Calne in Cambridge, England in 1963 and 1965 respectively. Liver transplantation is the only option for those with irreversible liver failure. Most transplants are done for chronic liver diseases leading to cirrhosis, such as chronic hepatitis C, alcoholism, autoimmune hepatitis, and many others. Less commonly, liver transplantation is done for fulminant hepatic failure, in which liver failure occurs over days to weeks.
   Liver allografts for transplant usually come from non-living donors who have died from fatal brain injury. Living donor liver transplantation is a technique in which a portion of a living person's liver is removed and used to replace the entire liver of the recipient. This was first performed in 1989 for pediatric liver transplantation. Only 20% of an adult's liver (Couinaud segments 2 and 3) is needed to serve as a liver allograft for an infant or small child.
   More recently, adult-to-adult liver transplantation has been done using the donor's right hepatic lobe which amounts to 60% of the liver. Due to the ability of the liver to regenerate, both the donor and recipient end up with normal liver function if all goes well. This procedure is more controversial as it entails performing a much larger operation on the donor, and indeed there have been at least 2 donor deaths out of the first several hundred cases. A recent publication has addressed the problem of donor mortality, and at least 14 cases have been found. The risk of postoperative complications (and death) is far greater in right sided hepatectomy than left sided operations.
   With the recent advances of non-invasive imaging, living liver donors usually have to undergo imaging examinations for liver anatomy to decide if the anatomy is feasible for donation. The evaluation is usually performed by multi-detector row computed tomography (MDCT) and magnetic resonance imaging (MRI). MDCT is good in vascular anatomy and volumetry. MRI is used for biliary tree anatomy. Donors with very unusual vascular anatomy, which makes them unsuitable for donation, could be screened out to avoid unnecessary operation. Image:LDLTA.jpg|MDCT image. Arterial anatomy contraindicated for liver donation. Image:LDLTP.jpg|MDCT image. Portal venous anatomy contraindicated for liver donation. Image:LDLT volume measure.jpg|MDCT image. 3D image created by MDCT can clearly visualize the liver, measure the liver volume, and plan the dissection plane to facilitate the liver transplantation procedure.

Development

Fetal blood supply

In the growing fetus, a major source of blood to the liver is the umbilical vein which supplies nutrients to the growing fetus. The umbilical vein enters the abdomen at the umbilicus, and passes upward along the free margin of the falciform ligament of the liver to the inferior surface of the liver. There it joins with the left branch of the portal vein. The ductus venosus carries blood from the left portal vein to the left hepatic vein and then to the inferior vena cava, allowing placental blood to bypass the liver.
In the fetus, the liver develops throughout normal gestation, and doesn't perform the normal filtration of the infant liver. The liver doesn't perform digestive processes because the fetus doesn't consume meals directly, but receives nourishment from the mother via the placenta. The fetal liver releases some blood stem cells that migrate to the fetal thymus, so initially the lymphocytes, called T-cells, are created from fetal liver stem cells. Once the fetus is delivered, the formation of blood stem cells in infants shifts to the red bone marrow.
After birth, the umbilical vein and ductus venosus are completely obliterated two to five days postpartum; the former becomes the ligamentum teres and the latter becomes the ligamentum venosum. In the disease state of cirrhosis and portal hypertension, the umbilical vein can open up again.

Liver as food

Mammal and bird livers are commonly eaten as food by humans. Liver can be baked, broiled, or fried (often served as liver and onions) or eaten raw (liver sashimi), but is perhaps most commonly made into spreads (examples include liver pâté, foie gras, chopped liver, and leverpostej), or sausages such as Braunschweiger and liverwurst). Liver sausages may also be used as spreads.
Animal livers are rich in iron and Vitamin A, and cod liver oil is commonly used as a dietary supplement. Very high doses of Vitamin A can be toxic; in 1913, Antarctic explorers Douglas Mawson and Xavier Mertz were both poisoned, the latter fatally, from eating husky liver. In the US, the USDA specifies 3000 μg per day as a tolerable upper limit, which amounts to about 50 g of raw pork liver, or 30-90g of polar-bear liver. However, acute vitamin A poisoning isn't likely to result from liver consumption, since it's present in a less toxic form than in many dietary supplements.

Cultural allusions

In Greek mythology, Prometheus was punished by the gods for revealing fire to humans by being chained to a rock where a vulture (or an eagle) would peck out his liver, which would regenerate overnight. Curiously, the liver is the only human internal organ that actually can regenerate itself to a significant extent; this characteristic may have already been known to the Greeks due to survived injuries in battle.
   The Talmud (tractate Berakhot 61b) refers to the liver as the seat of anger, with the gallbladder counteracting this.
   In Arabic and Persian language, the liver is used in figurative speech to refer to courage and strong feelings, or "their best," for example "This Mecca has thrown to you the pieces of its liver!"
   The legend of Liver-Eating Johnson says that he'd cut out and eat the liver of each man killed.
   In the motion picture The Message, Hind bint Utbah is implied or portrayed eating the liver of Hamza ibn ‘Abd al-Muttalib during the Battle of Uhud. Inuit won't eat the liver of polar bears (due to the fact a polar bear's liver contains so much Vitamin A as to be poisonous to humans) or seals

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