Liver cell

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Learn about the liver, cells, structure, and functions.* y8 R: X. c, m" \; r* I/ I

- R! _) \  B! l8 rThe liver is the largest gland in the body, and is situated slightly below the diaphragm and anterior to the stomach. It consists of two lobes which are wedge-shaped. Two blood vessels enter the liver, namely the hepatic portal vein with dissolved food substances from the small intestine, and the hepatic artery, with oxygenated blood from the lungs. Two ducts originate in the liver, and these unite to form the common hepatic duct which opens, with the pancreatic duct, in the hollow side of the duodenum (the first section of the small intestine). The gall bladder lies inside the liver, and is the storage place for bile, which is formed by the liver cells.
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8 d8 W0 P. q. Q4 h' T1 jThe right lobe of the liver is larger than the left lobe. Each lobe is further divided into many small lobules, each being about the size of a pin-head, and consisting of many liver cells, with bile channels and blood channels between them. Permeating the entire liver structure is a system of blood capillaries, bile capillaries and lymph capillaries.
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' I6 e( F! k6 ?/ g" uThe liver cells secrete the bile, and this collects in the bile capillaries, which then unite, forming bile ducts. These bile ducts all eventually unite, forming the main hepatic duct, which gives off a branch, the cystic duct, on its way toward the hepatic duct. The cystic duct leads into the gall bladder. Where a cystic duct joins the hepatic duct, the two continue as the general bile duct, which then joins the pancreatic duct, forming a common duct that opens into the duodenum.6 @: i! O- ]5 d3 j7 h; `1 ~  @3 N
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The functions of the liver are varied, working closely with nearly every fundamental system and process in the human body, in particular homeostasis and the regulation of blood sugar.6 J' R; g  _- x

- E- J" d: O# l, F- D1. Regulation of blood sugar: The level of blood sugar stays at around 0.1%, and excess coming from the gut is stored as glycogen. The hormone called insulin - excreted by the pancreas - causes the excess glucose to turn into glycogen.; R" y7 W0 Y) s5 \+ U: F
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2. Regulation of lipids: Lipids are extracted from the blood and changed to carbohydrates, etc. as required or sent to fat storage sites if not needed straight away.4 n: }! a+ A2 R& d) \3 y
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3. Regulation of amino acids: a supply of amino acids in the blood is kept at a normal level. Any spare which has not been absorbed cannot be stored but is converted into the waste products, called urea when at the liver, and is then sent to the kidneys to be removed from the body as urine. The remainder of the amino acid molecule is not wasted; it is changed into a carbohydrate that can be used.
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2 ~  Q- E+ Y6 e9 E4. Production of heat: the liver is one of the hardest working regions of the body and produces a lot of waste heat. This is carried round the body in the blood and warms less active regions.
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3 ?3 y/ q% `4 a( T* w5 L5. Forms bile: bile consists of bile salts and the excretory bile pigments. It is important to speed up the digestion of lipids.' v* y- z) Q9 e4 C

; v8 t9 m5 v/ L0 B# N( z5 ^& m6. Forms cholesterol: this fatty substance is used in the cells. Excess amounts in the blood can cause the blood vessels to become blocked, leading to heart attacks, etc.
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/ B, Q( {8 G, F7 F0 r7. Removals of hormones, toxins, etc. The liver extracts many harmful materials from the blood and excretes them in the bile or from the kidneys.
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8. Formation of red blood cells in the young embryo while it is developing in the womb.9 E$ y) H4 j) g% _5 H8 A, u

* I/ j) G% E4 F% N! y& P$ L9. Making heparin: this is a substance that prevents the blood from clotting as it travels through the blood system.
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10. Removal of hemoglobin molecules: when red blood cells die, the hemoglobin is converted into bile pigments and the iron atoms are saved for future use.
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11. Storage of blood: the liver can swell to hold huge amounts of blood which can be released into the circulation if the body suddenly needs more, e.g. if it is wounded.2 P8 p4 a7 T3 F" m0 W* ~4 E

7 q# g# p# Z6 v, o: @; v$ O5 E12. Forms plasma proteins: the plasma proteins are used in blood clotting and in keeping the blood plasma constant. The main blood proteins include fibrinogen, prothrombin, albumens and globulins.  j. S6 p+ e/ L4 P3 S
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13. Storage of vitamins such as vitamin A and D. Vitamin A is also made in the liver from carotene, the orange-red pigment in plants. Vitamin B12 is also stored in the liver.
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What Are the Functions of a Liver Cell?' [( D+ K) `% i2 X  c
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he challenge with liver cells is that they get lonely very fast, making them very temperamental when they're outside the body. "Liver cells have been notoriously finicky," MIT engineering professor Sangeeta Bhatia, M.D., told Forbes Magazine in March 2009. She adds, when you take liver cells out of the body, "The cells are dying immediately, and function is lost on the order of hours." Researchers posit that they can use liver cells to create new livers for more than 16,000 patients on the liver transplant list, to develop vaccines for hepatitis C and malaria and to create better toxicity tests for new drugs--if only these liver cells would cooperate!2 H* D) p& o8 ]/ M2 I2 I; }, B
Hepatocytes5 n; q' q" k5 I; g  f/ N
It's no secret that liver cells are socialites that know how to throw a party. They like to have a number of supporting cells around them at all times. Hepatocytes (also called parenchymal cells) are the head honchos. These popular cells make up 70 to 80 percent of the liver's cytoplasmic mass and are involved in synthesizing protein, cholesterol, bile salts, fibrinogen, phospholipids and glycoproteins. In other words, hepatocytes ensure that our blood coagulates so we don't bleed to death, that cell communication is tip-top and that we are able to carry fats in the bloodstream. Other functions of the hepatocytes include the transformation of carbohydrates (from alanine, glycerol and oxaloacetate), protein storage, start of the formation and secretion of bile and urea, and detoxification and excretion of substances. Thanks to these main cells, we are able to fight off disease, produce waste, transport materials throughout the body and process everything from drugs and insecticides to steroids and pollutants.
" s9 F' O; c8 c; gLiver Endothelial Cells (LEC)& a4 ^7 C6 p- J1 {% n# o
Another type of liver cell is the endothelial cells. Since they do not have tight membranes, these cells act as "scavengers" of nearby cells-- ollecting and circulating hepatocytes in the blood, for instance. They're also chiefly responsible for transporting white blood cells and other material from the blood to the liver and for increasing the immune system's tolerance of the liver. They can absorb ligands, which serve as biological markers and binders for pharmaceutical drugs. When stimulated, endothelial cells secrete cytokines, which is a form of cellular communication signal.2 l+ l/ Q/ M) O) g
Kupffer Cells (KC)$ n" c' g: v# ~; o& ]+ X! ?: l$ G
Kupffer cells are located within the sinusoidal lining of the liver and hold a quarter of the liver lysosomes. The lysosomes digest and dispose of dying cells, unnecessary proteins, bacteria and foreign microbes. If stimulated, kupffer cells secrete mediators of the immune response system, and they can perform a complex array of functions--from disarming foreign substances to removing damaged red blood cells from circulation. In a way, the kupffer cells are like bodyguards and assassins for the hepatocytes, protecting them from invaders and cell refuse.
$ U# K* A% ^5 XHepatic Stellate Cells (HSC)) ^  o# z$ s: _" H  o/ C" A
Think of the hepatic stellate cells as the liver's reserve army. Most of the time, this 5 to 8 percent of the liver's cells just sit around in an inactive "quiescent" state, storing vitamin A and a number of important receptors. Yet when activated (by an event like liver injury), the cell promotes ion movement, the production of antibodies, genesis of natural killer T-cells and the proliferation of chemical responses to stress. Researchers believe that hepatic stellate cells play a key role in releasing collagen scar tissue and encouraging liver scarring.5 g; x- ?6 v. l2 v  {
Other Cells
3 U, h6 r3 s! V+ |6 k+ I3 D9 I7 UOther cells hanging out in the liver include epithelial cells of bile duct, endothelial cells of blood and lymphatic vessels, smooth muscle cells of arteries and veins, nerve cells, fibroblasts and inflammatory cells. This matrix of cells all working together is what really facilitates functionality in the liver. By cooperating, they can filter the blood, store vitamins and minerals, excrete harmful toxins, produce bile, transport materials, form compounds that help coagulate the blood and metabolize carbohydrates, fats and proteins.
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The functions of liver cells are very significant in medical research today. Currently, scientists are examining transplanted hepatocytes in hopes that they'll find their way to an injured liver, repair, remove waste and reproduce--thus negating the need for donor livers. Hepatocytes are the focus of hemophilia research as well, since they play such a key role in blood coagulation. They're also looking at how hepatocyte death and stellate cell proliferation contribute to inflammation, fibrosis and even cancer. Endothelial cells are being studied to search for ways to target liver injury with pharmaceutical drug treatments. Endothelial cells also promote early liver and pancreas formation, so unlocking the key as to how these cells work together to grow a new organ will answer many questions in the years to come.
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Read more: What Are the Functions of a Liver Cell? | eHow.com http://www.ehow.com/about_510655 ... .html#ixzz1Q4XsUMtI

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Liver-Cell Transplants Show Promise in Reversing Genetic Disease Affecting Liver and Lungs
2 i' L# u- L% _ScienceDaily (Apr. 23, 2011) — Transplanting cells from healthy adult livers may work in treating a genetic liver-lung disorder that affects millions of people worldwide, according to an animal study in the April 18 online edition of the Journal of Clinical Investigation. Jayanta Roy-Chowdhury, M.D. , professor of medicine and of genetics at Albert Einstein College of Medicine of Yeshiva University, is the study's senior author.
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+ g' v; \. `/ D) [The genetic disorder, alpha-1 antitrypsin (AAT) deficiency, is the most common potentially lethal hereditary disease among Caucasians, affecting an estimated 100,000 people in the United States and 3.4 million people worldwide. AAT is a protein made by the liver that is essential for lung health. In AAT deficiency, the liver produces a misshapen form of AAT that cannot enter the bloodstream and instead gets stuck inside liver cells, causing two major problems:# r9 _9 B+ u8 ?
AAT accumulates in the liver, leading to fibrosis (development of scar tissue) and liver failure;$ c* W- f7 u# ]3 Q& t
Too little AAT reaches the lungs, where it's needed to rein in elastase, an enzyme produced by white blood cells. Elastase helps kill bacteria in the lungs, but uncontrolled elastase activity can damage lung tissue and lead to severe emphysema (chronic obstructive pulmonary disease).; c* T) H" ]  W! [$ P
In the study, Dr. Roy-Chowdhury and his colleagues tested cell therapy on transgenic mice whose liver cells (hepatocytes) had been engineered to produce mutant human AAT, resulting in liver fibrosis. When the mice were given infusions of hepatocytes harvested from the livers of healthy mice, the transplanted cells proliferated in the host liver, progressively replacing diseased hepatocytes. Most importantly, said Dr. Roy-Chowdhury, the transplanted cells reversed the fibrosis that had developed.. b  N& W( {$ J/ r
Current therapy for AAT deficiency consists of life-long injections of a genetically engineered version of AAT called Prolastin. "This very expensive therapy slows progression of the lung disease in some patients but does not have any beneficial effect on the liver disease," said Dr. Roy-Chowdhury. The only other therapy for AAT deficiency is combined lung-liver transplantation, which is reserved for the sickest patients.
5 z5 m. d# L! Y( P"These promising results in animals indicate that it may be worthwhile to investigate the usefulness of hepatocyte transplantation for AAT deficiency as well as a variety of other inherited liver-based disorders," said Dr. Roy-Chowdhury.
. i2 j: q/ C" A$ zThe title of the paper is "Spontaneous hepatic repopulation in transgenic mice expressing mutant human alpha 1-anti-trypsin by wildtype donor hepatocytes." Other Einstein researchers involved in the study are Jianqiang Ding, M.D., Ph.D., Namita Roy-Chowdhury, Ph.D., Yesim Avsar, M.D., and Chandan Guha, M.B., B.S., Ph.D. The research was supported by the National Institutes of Health, the National Institute of Diabetes, Digestive and Kidney Diseases, the New York Stem Cell Foundation, the Oxalosis and Hyperoxaluria Foundation, and the United States Department of Defense.

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Liver cells breakthrough raises hope) D4 Q& L: X9 o$ i$ P+ c8 }; R, {7 O
Nicky Park
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  w9 D6 s0 r$ \" M# ]% S  O, [4 A* m! WSCIENTISTS have been able to convert skin cells into liver cells, a breakthrough that could one day eliminate the need for organ transplants.: {* n0 e! o; C" C+ x; r, w
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A study using mice at the Shanghai Institute for Biological Sciences successfully generated the main type of liver cell - called a hepatocyte - from a skin cell. According to the study, published this week in Nature, ''when transplanted into mouse models of liver injury, the hepatocyte-like cells can repopulate the livers and restore their function.'', Z8 }5 P4 n3 Y( u* c8 K

4 s' Y1 j& Q# [& o) e8 ~$ K$ g8 fAustralian liver expert Professor Geoff McCaughen said while stem cells have been seen to make the transition, this was the first time the ''reprogramming'' technique worked with skin cells.
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9 d' ^+ r1 n$ i4 f% D''They're not perfectly functional like a normal liver cell, but they're probably 50 per cent or more there,'' said Professor McCaughen, head of the liver transplant unit at Sydney's Royal Prince Alfred Hospital.
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3 W' w' l3 r8 S3 ?( H''The genes which are used in programming and making it [a] liver cell … those genes have been put in to a skin cell and made functional,'' he said.
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The liver makes proteins, produces blood-clotting factors, metabolises glucose, gets rid of toxins and maintains blood sugar and energy levels.+ |: t& q) W3 E* I7 c7 W* w

9 v; Y! v3 c; Z4 h) g7 ?5 V! s, j''You can't live without these crucial liver cells, called hepatocytes, without them you die - this is liver failure,'' he said.
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Researchers would now need to test the function of the reprogrammed cells on a mouse that had been subjected to the cause of liver failure.
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''The concept would be that they would be injected and then they would populate the liver and generate new liver function and improve liver function.
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''That would be the Holy Grail - that they would stop the liver failing altogether, and the patient would not need a liver transplant or die.''* x% g  y" \3 e& F: }% V+ N

$ Z4 S9 h9 S, D# R( R/ @( x  ?: qAbout 200 people are on the waiting list for liver transplants in Australia, and 10 per cent of them would die while in line, Professor McCaughen said.
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