Steatosis
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2008-07-01T13:49:56Z
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[[Image:Liver_steatosis_fatty_change.jpg|thumb|250px|right|Histological section of a murine liver showing severe steatosis. The clear vacuoles would have contained lipid in the living cells, however the histological fixation caused it to be dissolved and hence only empty spaces remain]]
In [[cell (biology)|cellular]] [[pathology]], '''steatosis''' (also called ''fatty change'', ''fatty degeneration'' or ''adipose degeneration'') is the process describing the abnormal retention of [[lipid]]s within a cell. It reflects an impairment of the normal processes of [[synthesis]] and elimination of [[triglyceride]] fat. Excess lipid accumulates in [[vesicle (biology)|vesicle]]s that displace the [[cytoplasm]]. When the vesicles are large enough to distort the [[cell nucleus|nucleus]], the condition is known as '''macrovesicular steatosis''', otherwise the condition is known as '''microvesicular steatosis'''. Whilst not particularly detrimental to the cell in mild cases, large accumulations can disrupt cell constituents, and in severe cases the cell may even burst.
The risk factors associated with steatosis are varied, and include [[diabetes mellitus]],<ref name="araya">{{cite journal | author=Araya Q AV ''et al.''| title=Glucose tolerance alterations and frequency of metabolic syndrome among patients with non alcoholic fatty liver disease| journal=Rev Med Chil.| year=2006| volume=134| issue=9| url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17167710| pages=1092–1098}}</ref> protein malnutrition,<ref name="conde">{{cite journal | author=Conde Martel A ''et al.''| title=Liver changes in protein malnutrition. An experimental study in rats| journal=Nutr Hosp. | year=1993| volume=8| issue=6| url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=8373879| pages=358–363}}</ref> hypertension<ref name="brookes">{{cite journal | author=MJ Brookes, BT Cooper| title=Hypertension and fatty liver: guilty by association?| journal=J Hum Hypertens| year=2007| volume=21| issue=4| url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17273155| pages=264–270| doi=10.1038/sj.jhh.1002148}}</ref> cell toxins, obesity,<ref name="saadeh">{{cite journal | author=S Saadeh| title=Nonalcoholic Fatty liver disease and obesity| journal=Nutr Clin Pract. | year=2007| volume=22| issue=1| url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17242448| pages=1–10| doi=10.1177/011542650702200101| pmid=17242448}}</ref> and [[anoxia]].<ref name="robspath">{{cite book | title=Robbins Pathologic Basis of Disease| last=Cotran| coauthors=Kumar, Collins| publisher=W.B Saunders Company| location=Philadelphia| id=0-7216-7335-X}}</ref> As the liver is the primary organ of [[lipid metabolism]] it is most often associated with steatosis, however it may occur in any organ, commonly the kidneys, heart, and muscle.<ref name="robspath"> </ref>
== Pathogenesis ==
No single mechanism leading to steatosis exists, rather a varied multitude of pathologies disrupt normal lipid movement through the cell and cause accumulation. These mechanisms can be separated on whether they ultimately cause an oversupply of lipid which can not be removed quickly enough (too much in), or whether they cause a failure in lipid breakdown (not enough used).
Oversupply of lipid may occur due to obesity, insulin resistance, or [[alcoholism]]. Nutrient malnutrition may also cause the mobilisation of fat from [[adipocyte]]s and create a local oversupply in the liver where lipid metabolism occurs. Excess alcohol over a long period of time can induce steatosis. The breakdown of large amounts of [[ethanol]] in alcoholic drinks produces large amounts of chemical energy, in the form of [[NADH]], signalling to the cell to inhibit the breakdown of [[fatty acid]]s (which also produces energy) and simultaneously increase the synthesis of [[fatty acid]]s. This "false sense of energy" results in more lipid being created than is needed.
Failure of lipid metabolism can also lead to the mechanisms which would normally utilise or remove lipids becoming impaired, resulting in the accumulation of unused lipids in the cell. Certain toxins, such as alcohols, [[carbon tetrachloride]], [[aspirin]], and [[diphtheria toxin]], interfere with cellular machinery involved in lipid metabolism. In those with [[Gaucher's disease]], the [[lysosome]]s fail to degrade lipids and steatosis arises from the accumulation of [[glycolipid]]s. Protein malnutrition, such as that seen in [[kwashiorkor]], results in a lack of precursor [[apoproteins]] within the cell, therefore unused lipids which would normally participate in [[lipoprotein]] synthesis begin to accumulate.
== Appearance ==
<!-- [[Image:Livers.jpg|thumb|250px|The duck liver on the left has been fattened by force feeding to make [[foie gras]], compared to an ordinary duck liver on the right.]] -->[[histology|Histologically]], steatosis is physically apparent as lipid within membrane bound [[liposome]]s of [[parenchyma|parenchymal]] cells<ref name="robspath"> </ref>. When this tissue is [[Staining|fixed and stained]] to be better viewed under a microscope, the lipid is usually dissolved by the solvents used to prepare the sample. As such, samples prepared this way will appear to have empty holes within the cells where the lipid has been cleared. Special lipid stains, such as [[Sudan stain]]s and [[Staining#Osmium_tetroxide|osmium tetroxide]] are able to retain and show up lipid droplets, hence more conclusively indicating the presence of lipids. Other intracellular accumulations, such as water or [[glycogen]], can also appear as clear vacuoles, therefore it becomes necessary to use stains to better decide what is accumulating.
Grossly, steatosis causes organ enlargement and lightening in colour<ref name="robspath"> </ref>. This is due to the high lipid content increasing the organ's volume and becoming visible to the unaided eye. In severe cases, the organ may become vastly enlarged, greasy, and yellow in appearance.
== See also ==
* [[Intracellular fat]]
* [[Fatty liver]]
* [[Lipid metabolism]]
* [[Non-alcoholic fatty liver disease]]
* [[Visceral_fat|Visceral fat]]
* [[Fat globules]]
== References ==
{{reflist|1}}
[[Category:Pathology]]
[[Category:Histopathology]]
[[es:Esteatosis]]
[[fr:Stéatose hépatique]]
[[it:Steatosi]]
[[ja:脂肪変性]]
[[no:Steatose]]
[[pt:Esteatose]]