Adipose tissue
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[[Image:Illu connective tissues 1.jpg|thumb|390px|Adipose tissue is one of the main types of [[connective tissue]].]]
:''"Adipose" redirects here. For the Doctor Who monster, see [[#Cultural and social role|below]], or "[[Partners in Crime (Doctor Who)|Partners in Crime]]".''
In [[histology]], '''adipose tissue''' or '''fat''' is loose [[connective tissue]] composed of [[adipocyte]]s. Adipose tissue is derived from lipoblasts. Its main role is to store [[energy]] in the form of [[fat]], although it also cushions and [[Thermal insulation|insulates]] the body. [[Obesity]] or being [[overweight]] in humans and most animals does not depend on body weight but on the amount of body fat—specifically, adipose tissue. Two types of adipose tissue exist: [[white adipose tissue]] (WAT) and [[brown adipose tissue]] (BAT). Adipose tissue also serves as an important [[endocrine]] organ<ref>{{cite journal |author=Kershaw EE, Flier JS |title=Adipose tissue as an endocrine organ |journal=J. Clin. Endocrinol. Metab. |volume=89 |issue=6 |pages=2548–56 |year=2004 |pmid=15181022 |doi=10.1210/jc.2004-0395}}</ref> by producing [[hormone]]s such as [[leptin]], [[resistin]] and the [[cytokine]] [[TNF-alpha|TNFα]]. The formation of adipose tissue appears to be controlled by the [[adipose gene]].
==Anatomical features==
In humans, adipose tissue is located beneath the [[skin]] ([[subcutaneous fat]]), and is also found around internal [[Organ (anatomy)|organ]]s ([[visceral fat]]). Adipose tissue is found in specific locations which are referred to as 'adipose depots.' Adipose tissue contains several cell types, with the highest percentage of cells being [[adipocyte]]s, which contain fat droplets. Other cell types include [[fibroblasts]], [[macrophages]] and [[endothelial cells]]. Adipose tissue contains many small [[blood vessel]]s. In the [[integumentary system]], which includes the skin, it accumulates in the deepest level, the [[subcutaneous]] layer, providing insulation from heat and cold. Around organs, it provides protective padding. However, its main function is to be a reserve of lipids, which can be burned to meet the energy needs of the body. Adipose depots in different parts of the body have different biochemical profiles.
===Mice===
In [[mouse|mice]], there are eight major adipose depots, four of which are within the [[abdominal cavity]]: the paired gonadal depots are attached to the [[uterus]] and [[ovaries]] in females and the [[epididymis]] and [[testes]] in males, the paired retroperitoneal depots are found along the [[dorsal]] wall of the abdomen, surrounding the kidney, and when massive extend into the pelvis. The mesenteric depot forms a glue-like web that supports the [[intestine]]s, and the omental depot, which originates near the [[stomach]] and [[spleen]] and when massive extends into the ventral abdomen. Both the mesenteric and omental depots incorporate much [[lymphoid tissue]] as lymph nodes and milky spots respectively. The two superficial depots are the paired inguinal depots, which are found anterior to the upper segment of the hind limbs (underneath the skin) and the subscapular depots, paired medial mixtures of brown adipose tissue adjacent to regions of white adipose tissue, which are found under the [[skin]] between the dorsal crests of the scapulae. The layer of brown adipose tissue in this depot is often covered by a “frosting” of white adipose tissue, sometimes these two types of fat (brown and white) are hard to distinguish. The inguinal depots enclose the inguinal group of lymph nodes. Minor depots include the [[pericardial]] which surrounds the heart, and the paired popliteal depots, between the major [[muscle]]s behind the knees, each containing one large [[lymph node]]<ref>{{cite book | last = Pond | first = Caroline M. | authorlink = Caroline M. Pond | title = The Fats of Life | publisher = Cambridge University Press | date = 1998 | isbn = 0521635772}}</ref>. Of all the depots in the mouse, the gonadal depots are the largest and the most easily dissected<ref>{{cite journal | last = Cinti | first = S | year = 2005 | month = July | title = The adipose organ | journal = Prostaglandins, leukotrienes, and essential fatty acids | volume = 73 | issue = 0952-3278 | pages = 9–15 | publisher = Elsevier Science | pmid = 15936182 | url = http://www.ncbi.nlm.nih.gov/pubmed/15936182 | doi = 10.1016/j.plefa.2005.04.010}}</ref>, comprising about 30% of dissectible fat<ref>{{cite journal | last= Bachmanov | first= Alexander | authorlink= Alexander Bachmanov | coauthors= D. R. Reed, M. G. Tordoff, R. A. Price | year= 2001 | month= March | title= Nutrient preference and diet-induced adiposity in C57BL/6ByJ and 129P3/J mice | journal= Physiology & Behavior | volume= 72 | issue= 0031-9384 | pages= 603–613 | pmid=11282146 | url= http://www.ncbi.nlm.nih.gov/pubmed/11282146 | doi= 10.1016/S0031-9384(01)00412-7}}</ref>.
===Obesity===
In a severely [[obese]] [[person]], excess adipose tissue hanging downward from the abdomen is referred to as a [[panniculus]] (or [[pannus]]). A panniculus complicates surgery of the morbidly obese. The panniculus may remain as a literal "apron of skin" if a severely obese person quickly loses large amounts of fat (a common result of [[gastric bypass surgery]]). This condition cannot be effectively corrected through diet and exercise alone, as the panniculus consists of adipocytes and other supporting cell types shrunken to their minimum volume and diameter. Reconstructive surgery is one method of treatment.
==Physiology==
{{Refimprove|date=July 2007}}
[[Free fatty acid]] is "liberated" from [[lipoprotein]]s by [[lipoprotein lipase]] (LPL) and enters the adipocyte, where it is reassembled into [[triglyceride]]s by [[ester]]ifying it onto [[glycerol]]. Human fat tissue contains about 87% lipids.
In humans, lipolysis is controlled though the balanced control of lipolytic B-adrenergic receptors and a2A-andronergic receptor mediated antilipolysis.
Fat is not laid down when there is a surplus available and stored passively until it is needed; rather it is constantly being stored in and released from each cell.
Fat cells have an important [[physiology|physiological]] role in maintaining triglyceride and [[free fatty acid]] levels, as well as determining [[insulin resistance]]. [[Abdomen|Abdominal]] fat has a different [[metabolism|metabolic]] profile—being more prone to induce insulin resistance. This explains to a large degree why [[central obesity]] is a marker of impaired glucose tolerance and is an independent risk factor for [[cardiovascular disease]] (even in the absence of [[diabetes mellitus]] and [[hypertension]]).{{Fact|date=April 2008}}
Recent advances in biotechnology have allowed for the harvesting of [[adult stem cell]]s from adipose tissue, allowing stimulation of tissue regrowth using a patient's own cells. The use of a patient's own cells reduces the chance of tissue rejection and avoids the ethical issues associated with the use of human [[embryonic stem cell]]s.
Adipose tissue is the greatest [[peripheral]] source of [[aromatase]] in both males and females contributing to the production of [[estradiol]].
[[Adipose derived hormones]] include:
* [[Adiponectin]]
* [[Resistin]]
* [[Angiotensin]]
* [[Plasminogen activator inhibitor-1]] (PAI-1)
* [[TNF-alpha|TNFα]]
* [[Interleukin|IL-6]]
* [[Leptin]]
* [[Estradiol]] (E2)
Adipose tissues also secrete a type of [[cytokine]]s (cell-to-cell signalling proteins) called [[adipokine]]s (adipocytokines) which play a role in obesity-associated complications.
===Brown fat===
A specialised form of adipose tissue in human [[infant]]s, and some [[hibernating]] animals, is [[brown fat]] or [[brown adipose tissue]]. It is located mainly around the neck and large blood vessels of the thorax. This specialised tissue can generate heat by "uncoupling" the [[respiratory chain]] of [[oxidative phosphorylation]] within [[mitochondria]], leading to the breakdown of fatty acids. This thermogenic process may be vital in neonates exposed to the cold, who then require this thermogenesis to keep warm as they are unable to [[shivering|shiver]], or take other actions to keep themselves warm.<ref>Himms-Hagen, J. (August 1990) "Brown adipose tissue thermogenesis: interdisciplinary studies" ''The FASEB Journal'' (Federation of American Societies for Experimental Biology) 4(11): pp. 2890-2898</ref>
Attempts to stimulate this process [[pharmacology|pharmacologically]] have so far been unsuccessful, but might in the future be a target of [[weight loss]] therapy.
===Genetics===
In 2007, researchers isolated the adipose gene, which apparently serves to keep animals lean during times of plenty. Increased adipose gene activity was associated with slimmer individuals.<ref>Suh, Jae Myoung ''et al.'' (September 2007) "Adipose Is a Conserved Dosage-Sensitive Antiobesity Gene" ''Cell Metabolism'' 6(3): pp. 195-207</ref>
===Physical properties===
Adipose tissue has a density of ~0.9g/ml <ref name=fatvsmuscle> [http://answers.google.com/answers/threadview?id=576481 Google Answers: Muscle Density vs. Fat Density]</ref>. Thus, a person with much adipose tissue will float easier than a person with lot of [[muscular tissue]], since muscular tissue has a density of 1.06 g/ml<ref name=fatvsmuscle/>.
==Cultural and social role==
Excess adipose tissue on a human can lead to medical problems; however, a round or large figure does not of itself imply a medical problem, and is sometimes not primarily caused by adipose tissue. For a discussion of the aesthetic and medical significance of body shape, see [[dieting]] and [[obesity]].
The term "adipose" was also used as the name of a character in a 2008 episode of the British science fiction series ''[[Doctor Who]]'', [[Partners in Crime (Doctor Who)|Partners in Crime]]. Aliens called "the Adipose" are part of a plan involving diet pills, hence the link with fat tissue.
<!--Adipose tissue, because of its association with high [[food energy]] intake and low physical exertion, historically was considered an [[indication]] of wealth and privilege.
-->
==Additional images==
<gallery>
Image:Gray940.png|diagrammatic sectional view of the skin (magnified).
Image:Yellow adipose tissue in paraffin section - lipids washed out.jpg|Yellow adipose tissue in paraffin section
</gallery>
==References==
{{reflist|2}}
<div class="references-small">
#<li value="4">Bachmanov AA, Reed DR, Tordoff MG, Price RA, Beauchamp GK (2001) Nutrient preference and diet-induced adiposity in C57BL/6ByJ and 129P3/J mice. Physiology and Behavior 72, 603-613
#Cinti S (1999) The adipose organ. Editrice Kurtis, Milano
#Pond CM (1998) The fats of life. Cambridge University Press, Cambridge
</div>
==See also==
* [[Apelin]]
* [[Bioelectrical impedance analysis]]: a method to measure body fat percentage.
* [[Body fat meter]]
* [[Body fat percentage]]
* [[Cellulite]]
* [[Obesity]]
* [[Steatosis]] (Also called ''fatty change'', ''fatty degeneration'' or ''adipose degeneration'').
* [[Stem Cells]]
* [[Subcutaneous fat]]
* [[Visceral fat]]
{{endocrine_system}}
{{Connective tissue}}
[[Category:Tissues]]
[[Category:Obesity]]
[[ca:Teixit adipós]]
[[cs:Tuková tkáň]]
[[da:Fedtvæv]]
[[de:Fettgewebe]]
[[el:Λιπώδης ιστός]]
[[es:Tejido adiposo]]
[[fr:Tissu adipeux]]
[[gl:Tecido adiposo]]
[[it:Tessuto adiposo]]
[[lt:Riebalinis audinys]]
[[nl:Vetweefsel]]
[[ja:脂肪組織]]
[[no:Fettvev]]
[[pl:Tkanka tłuszczowa]]
[[pt:Tecido adiposo]]
[[ru:Жировая ткань]]
[[fi:Rasvakudos]]
[[sv:Fettvävnad]]
[[tr:Yağ doku]]