Hepatocyte 501136 214438934 2008-05-23T15:39:11Z 129.67.38.107 /* Carbohydrate metabolism */ {{Refimprove|date=March 2008}} [[Image:Sinusoid.jpeg|thumb|300px|Sinusoid of a [[rat]] liver with fenestrated endothelial cells. Fenestrae are approx 100 [[Nanometre|nm]] diameter, and the sinusoidal width 5 [[Micrometre|µm]]. Scanning electron micrograph by Robin Fraser, [[University of Otago]].]] [[Image:Human liver.jpg|thumb|300px|Human liver]] '''Hepatocytes''' make up 70-80% of the [[cytoplasm]]ic mass of the [[liver]]. These cells are involved in [[protein synthesis]], [[protein storage]] and transformation of [[carbohydrate]]s, synthesis of [[cholesterol]], [[bile salt]]s and [[phospholipid]]s, and detoxification, modification and excretion of exogenous and endogenous substances. The hepatocyte also initiates the formation and secretion of [[bile]]. ==Hepatocyte histology== Hepatocytes display an [[eosinophilic]] cytoplasm, reflecting numerous [[mitochondria]], and [[basophilic]] stippling due to large amounts of [[rough endoplasmic reticulum]] and free [[ribosomes]]. Brown [[lipofuscin]] granules are also observed (with increasing age) together with irregular unstained areas of cytoplasm; these correspond to cytoplasmic [[glycogen]] and [[lipid]] stores removed during histological preparation. The average life span of the hepatocyte is 5 months; they are able to regenerate. Hepatocyte [[cell nucleus|nuclei]] are round with dispersed [[chromatin]] and prominent [[nucleoli]]. Anisokaryosis is common and reflects [[tetraploidy]] & [[polyploidy]], a normal feature of over 50% of hepatocytes. Binucleate cells are also common. Hepatocytes are organised into plates separated by vascular channels ([[Liver sinusoid|sinusoids]]), an arrangement supported by a reticulin (collagen type III) network. The hepatocyte plates are one cell thick in mammals and two cells thick in the chicken. Sinusoids display a discontinuous, fenestrated [[endothelial]] cell lining. The endothelial cells have no [[basement membrane]] and are separated from the hepatocytes by the space of Disse which drains [[lymph]] into the portal tract [[lymphatics]]. Kupffer cells are scattered between endothelial cells; they are part of the [[reticuloendothelial system]] and phagocytose spent [[erythrocytes]]. Stellate (Ito) cells store [[vitamin A]] and produce [[extracellular matrix]] and [[collagen]]; they are also distributed amongst endothelial cells but are difficult to visualise by light microscopy. Hepatocytes are an important physiological example for evalutation of both biological and metabolic effects of [[xenobiotics]]. They do not proliferate in culture. Hepatocytes are intensely sensitive to damage during the cycles of cryopreservation including freezing and thawing. Even after the addition of classical cryoprotectants there is still damage done while being cryopreserved. <ref> Hamel et al; "Wheat Extracts as an Efficient Cryoprotective Agent for Primary Cultures of Rat Hepatocytes": published online 21 Aug 2006 in Wiley Interscience www.interscience.wiley.com. Department des sciences bogiques, Montreal University. </ref> ==Protein synthesis== The hepatocyte is a [[cell (biology)|cell]] in the [[body]] that manufactures [[serum albumin]], [[fibrinogen]], and the [[prothrombin]] group of [[clotting factor]]s. It is the main site for the synthesis of [[lipoprotein]]s, [[ceruloplasmin]], [[transferrin]], [[Complement system|complement]] and [[glycoprotein]]s. Hepatocytes manufacture their own structural proteins and intracellular [[enzyme]]s. Synthesis of proteins is undertaken by the [[rough endoplasmic reticulum]] (RER), and both the rough and [[smooth endoplasmic reticulum]] (SER) are involved in secretion of the proteins formed. The [[endoplasmic reticulum]] (ER) is involved in conjugation of proteins to lipid and carbohydrate moieties synthesized by, or modified within, the hepatocytes. ==Carbohydrate metabolism== {{seealso|Lipogenesis}} The [[liver]] forms fatty acids from [[carbohydrate]]s and synthesizes triglycerides from fatty acids and glycerol. Hepatocytes also synthesize [[apoprotein]]s with which they then assemble and export lipoproteins ([[Very low density lipoprotein|VLDL]], [[High density lipoprotein|HDL]]). The liver is also the main site in the body for [[gluconeogenesis]], the formation of carbohydrates from precursors such as [[alanine]], [[glycerol]] and [[oxaloacetate]]. ==Lipid metabolism== The liver receives many [[lipid]]s from the systemic circulation and metabolizes [[chylomicron]] remnants. It also synthesizes [[cholesterol]] from [[acetate]] and then further synthesizes [[bile salt]]s. The liver is the sole site of formation of bile salts. ==Detoxification== Hepatocytes have the ability to metabolize, detoxify, and inactivate exogenous compounds such as [[medication|drugs]] and [[insecticide]]s, and endogenous compounds such as [[steroid]]s. The drainage of the [[intestinal]] [[venous]] [[blood]] into the [[liver]] requires efficient detoxification of miscellaneous absorbed substances to maintain [[homeostasis]] and protect the body against ingested toxins. One of the detoxifying functions of hepatocytes is to modify ammonia into [[urea]] for excretion. ==Additional images== <gallery> Image:Schemic diagram of Biliary system.jpg|Schemic diagram of Biliary system </gallery> ==References== {{Reflist}} ==External links== * {{BUHistology|22101ooa}} - "Ultrastructure of the Cell: hepatocytes and sinusoids" * [http://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/histo_hcytes.html Hepatic Histology: Hepatocytes (Colorado State University] {{Digestive glands}} [[Category:Animal cells]] [[Category:Human cells]] [[Category:Tissues]] [[Category:Hepatology]] [[ca:Hepatòcit]] [[cs:Hepatocyt]] [[de:Hepatozyt]] [[es:Hepatocito]] [[fr:Hépatocyte]] [[it:Epatocita]] [[ja:肝細胞]] [[lt:Hepatocitas]] [[mk:Хепатоцит]] [[pl:Hepatocyt]] [[ru:Гепатоциты]] [[sh:Hepatocit]] [[fi:Maksasolu]] [[sv:Hepatocyt]] [[tr:Hepatosit]]