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{{redirect|Viscera|other meanings|Viscera (disambiguation)}} |
{{redirect|Viscera|other meanings|Viscera (disambiguation)}} |
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{{Redirect|Organs|other uses|Organ (disambiguation){{!}}Organ}} |
{{Redirect|Organs|other uses|Organ (disambiguation){{!}}Organ}} |
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{{TAFI}} |
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== Overview == |
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{{Infobox anatomy |
{{Infobox anatomy |
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| Name = Organ |
| Name = Organ |
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'''Organs''' are |
'''Organs''' are groups of [[Tissue (biology)|tissues]] with similar functions. Plant and animal life relies on many organs that coexist in [[organ system]]s.<ref>{{cite book |
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| author = Widmaier EP |
| author = Widmaier EP |
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|author2=Raff H |author3=Strang KT |
|author2=Raff H |author3=Strang KT |
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| edition = 12th |
| edition = 12th |
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| isbn = 978-0-07-128366-3 |
| isbn = 978-0-07-128366-3 |
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}}{{pn|date=May 2015}}</ref> |
}}{{pn|date=May 2015}}</ref> |
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Organs are composed of main tissue, [[parenchyma]], and "sporadic" tissues, [[stroma (animal tissue)|stroma]]. The main tissue is that which is unique for the specific organ, such as the [[myocardium]], the main tissue of the [[heart]], while sporadic tissues include the [[nerve tissue|nerves]], [[blood vessels]], and [[connective tissue]]s. The main tissues that make up an organ tend to have common [[embryology|embryologic]] origins, such as arising from the same [[germ layer]]. Functionally-related organs often cooperate to form whole organ systems. Organs exist in all [[organism]]s. In [[unicellular organism|single-celled organisms]] such as [[bacteria]], the [[analogy (biology)|functional analogue]] of an organ is known as an [[organelle]]. In plants there are three main organs.<ref name="Botany">{{cite web|title=Botany/Plant structure - Wikibooks, open books for an open world|url=https://en.wikibooks.org/wiki/Botany/Plant_structure|website=en.wikibooks.org|language=en}}</ref> A hollow organ is an internal organ that forms a hollow tube, or pouch such as the [[stomach]], [[intestine]], or [[urinary bladder|bladder]]. |
Organs are composed of main tissue, [[parenchyma]], and "sporadic" tissues, [[stroma (animal tissue)|stroma]]. The main tissue is that which is unique for the specific organ, such as the [[myocardium]], the main tissue of the [[heart]], while sporadic tissues include the [[nerve tissue|nerves]], [[blood vessels]], and [[connective tissue]]s. The main tissues that make up an organ tend to have common [[embryology|embryologic]] origins, such as arising from the same [[germ layer]]. Functionally-related organs often cooperate to form whole organ systems. Organs exist in all multicellular [[organism]]s. In [[unicellular organism|single-celled organisms]] such as [[bacteria]], the [[analogy (biology)|functional analogue]] of an organ is known as an [[organelle]]. In plants there are three main organs.<ref name="Botany">{{cite web|title=Botany/Plant structure - Wikibooks, open books for an open world|url=https://en.wikibooks.org/wiki/Botany/Plant_structure|website=en.wikibooks.org|language=en}}</ref> A hollow organ is an internal organ that forms a hollow tube, or pouch such as the [[stomach]], [[intestine]], or [[urinary bladder|bladder]]. |
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In the study of [[anatomy]], the term ''viscus'' is used to refer to an internal organ, and ''viscera'' is the plural form.<ref>{{cite web |url=http://www.merriam-webster.com/dictionary/Viscus |title=Viscus - Definition |work=Merriam-Webster Online Dictionary |accessdate=14 December 2009}}</ref><ref>{{cite web |url=https://www.ncbi.nlm.nih.gov/mesh?term=viscera |title=Viscera |work=MeSH |accessdate=14 December 2009}}</ref> 79 organs have been identified in the human body.<ref>{{Cite news|url=https://www.bbc.com/news/health-38506708|title=New organ named in digestive system|date=2017|work=BBC News|access-date=2018-02-05|language=en-GB}}</ref> |
In the study of [[anatomy]], the term ''viscus'' is used to refer to an internal organ, and ''viscera'' is the plural form.<ref>{{cite web |url=http://www.merriam-webster.com/dictionary/Viscus |title=Viscus - Definition |work=Merriam-Webster Online Dictionary |accessdate=14 December 2009}}</ref><ref>{{cite web |url=https://www.ncbi.nlm.nih.gov/mesh?term=viscera |title=Viscera |work=MeSH |accessdate=14 December 2009}}</ref> 79 organs have been identified in the human body.<ref>{{Cite news|url=https://www.bbc.com/news/health-38506708|title=New organ named in digestive system|date=2017|work=BBC News|access-date=2018-02-05|language=en-GB}}</ref> |
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==Structure== |
==Structure== |
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===Tissue=== |
===Tissue=== |
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In [[biology]], [[tissue (biology)|tissue]] is a cellular organizational level between [[cell (biology)|cells]] and complete organs. A tissue is an ensemble of similar cells and their [[extracellular matrix]] from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues. |
In [[biology]], [[tissue (biology)|tissue]] is a cellular organizational level between [[cell (biology)|cells]] and complete organs. A tissue is an ensemble of similar cells and their [[extracellular matrix]] from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues. |
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The study of human and animal tissues is known as [[histology]] or, in connection with disease, [[histopathology]]. For plants, the discipline is called [[plant anatomy]]. |
The study of human and animal tissues is known as [[histology]] or, in connection with disease, [[histopathology]]. For plants, the discipline is called [[plant anatomy|plant morphology]]. Classical tools for studying tissues include the [[Microtome#Applications|paraffin block]] ([[agarose]] gel is often used with plants<ref>{{Cite journal|last=Lišková|first=Desana|last2=Kollárová|first2=Karin|last3=Martinka|first3=Michal|last4=Sterckeman|first4=Thibault|last5=Lux|first5=Alexander|last6=Zelko|first6=Ivan|date=2012-07-01|title=An easy method for cutting and fluorescent staining of thin roots|url=https://academic.oup.com/aob/article/110/2/475/2769211|journal=Annals of Botany|language=en|volume=110|issue=2|pages=475–478|doi=10.1093/aob/mcs046|issn=0305-7364}}</ref><ref>{{Cite web|url=https://sites.lsa.umich.edu/schiefelbein-lab/rapid-preparation-of-transverse-sections-of-plant-roots/|title=Rapid Preparation of Transverse Sections of Plant Roots {{!}} Schiefelbein Lab|language=en-US|access-date=2019-03-19}}</ref>) in which tissue is embedded and then sectioned, the [[staining|histological stain]], and the [[Microscope|optical microscope]]. In the last couple of decades, developments in [[electron microscopy]], [[immunofluorescence]], and the use of [[microtome|frozen tissue sections]] have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of [[medical diagnosis]] and [[prognosis]]. |
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=== Organ systems === |
=== Organ systems === |
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{{See also|List of organs of the human body}} |
{{See also|List of organs of the human body}} |
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Two or more organs working together in the execution of a specific body function form an organ system, also called a [[biological system]] or body system. The functions of organ systems often share significant overlap. For instance, the [[nervous system|nervous]] and [[endocrine system]] both operate via a shared organ, the [[hypothalamus]]. For this reason, the two systems are combined and studied as the [[neuroendocrine system]]. The same is true for the [[musculoskeletal system]] because of the relationship between the [[muscular system|muscular]] and [[skeletal system]]s. |
Two or more organs working together in the execution of a specific body function form an organ system, also called a [[biological system]] or body system. The functions of organ systems often share significant overlap. For instance, the [[nervous system|nervous]] and [[endocrine system]] both operate via a shared organ, the [[hypothalamus]]. For this reason, the two systems are combined and studied as the [[neuroendocrine system]]. The same is true for the [[musculoskeletal system]] because of the relationship between the [[muscular system|muscular]] and [[skeletal system]]s. |
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Common organ system designations in plants includes the differentiation of shoot and root. All parts of the plant above ground (in non-[[epiphyte]]s), including the functionally distinct leaf and flower organs, may be classified together as the shoot organ system.<ref>{{Cite web|url=https://courses.lumenlearning.com/boundless-biology/chapter/the-plant-body/|title=The Plant Body {{!}} Boundless Biology|website=courses.lumenlearning.com|access-date=2019-03-19}}</ref> |
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==Function== |
==Function== |
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===Animals=== |
===Animals=== |
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[[File:Leber Schaf.jpg|thumb|The [[liver]] and [[gallbladder]] of a [[sheep]]]] |
[[File:Leber Schaf.jpg|thumb|The [[liver]] and [[gallbladder]] of a [[sheep]]]] |
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* [[Excretory system]]: [[kidney]]s, [[ureter]]s, [[urinary bladder|bladder]] and [[urethra]] involved in fluid balance, [[electrolyte]] balance and excretion of [[urine]]. |
* [[Excretory system]]: [[kidney]]s, [[ureter]]s, [[urinary bladder|bladder]] and [[urethra]] involved in fluid balance, [[electrolyte]] balance and excretion of [[urine]]. |
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* [[Lymphatic system]]: structures involved in the transfer of [[lymph]] between [[Tissue (biology)|tissues]] and the [[blood stream]], the lymph and the [[lymph node|nodes]] and [[lymph vessel|vessels]] that transport it including the [[Immune system]]: defending against [[disease]]-causing agents with [[leukocyte]]s, [[tonsil]]s, [[adenoid]]s, [[thymus]] and [[spleen]]. |
* [[Lymphatic system]]: structures involved in the transfer of [[lymph]] between [[Tissue (biology)|tissues]] and the [[blood stream]], the lymph and the [[lymph node|nodes]] and [[lymph vessel|vessels]] that transport it including the [[Immune system]]: defending against [[disease]]-causing agents with [[leukocyte]]s, [[tonsil]]s, [[adenoid]]s, [[thymus]] and [[spleen]]. |
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* [[Integumentary system]]: [[skin]], [[hair]] and [[nail (anatomy)|nails]] of mammals. Also [[scale (anatomy)| |
* [[Integumentary system]]: [[skin]], [[hair]] and [[nail (anatomy)|nails]] of mammals. Also [[scale (anatomy)|scales]] of [[fish]], [[reptile]]s, and [[bird]]s, and [[feather]]s of birds. |
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* [[Muscular system]]: movement with [[muscle]]s. |
* [[Muscular system]]: movement with [[muscle]]s. |
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* [[Nervous system]]: collecting, transferring and processing information with [[brain]], [[spinal cord]] and [[nerve]]s. |
* [[Nervous system]]: collecting, transferring and processing information with [[brain]], [[spinal cord]] and [[nerve]]s. |
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[[Image:Red Hibiscus in Chennai during Spring.JPG|thumb|right|The flower is the angiosperm's reproductive organ. This ''[[Hibiscus]]'' flower is hermaphroditic, and it contains [[stamen]] and [[Gynoecium|pistils]].]] |
[[Image:Red Hibiscus in Chennai during Spring.JPG|thumb|right|The flower is the angiosperm's reproductive organ. This ''[[Hibiscus]]'' flower is hermaphroditic, and it contains [[stamen]] and [[Gynoecium|pistils]].]] |
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[[Image:Equisetum telmateia strob.jpg|thumb|right|Strobilus of ''[[Equisetum telmateia]]'']] |
[[Image:Equisetum telmateia strob.jpg|thumb|right|Strobilus of ''[[Equisetum telmateia]]'']] |
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The study of plant organs is referred to as [[plant morphology]], rather than anatomy |
The study of plant organs is referred to as [[plant morphology]], rather than anatomy {{En dash}} as in [[animal]] systems. Organs of [[plant]]s can be divided into vegetative and reproductive. Vegetative plant organs include [[root]]s, [[plant stem|stems]], and [[leaf|leaves]]. The reproductive organs are variable. In [[flowering plant]]s, they are represented by the [[flower]], [[seed]] and [[fruit]]. In [[Pinophyta|conifers]], the organ that bears the reproductive structures is called a [[conifer cone|cone]]. In other divisions ([[phylum|phyla]]) of plants, the reproductive organs are called [[strobili]], in ''[[Lycopodiophyta]]'', or simply gametophores in [[moss]]es. |
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The vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as [[photosynthesis]], while the reproductive organs are essential in [[plant sexuality|reproduction]]. However, if there is [[asexual reproduction|asexual]] [[vegetative reproduction]], the vegetative organs are those that create the new generation of plants (see [[clonal colony]]). |
The vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as [[photosynthesis]], while the reproductive organs are essential in [[plant sexuality|reproduction]]. However, if there is [[asexual reproduction|asexual]] [[vegetative reproduction]], the vegetative organs are those that create the new generation of plants (see [[clonal colony]]). |
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==Society and culture== |
==Society and culture== |
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Many societies have a system for [[ |
Many societies have a system for [[organ donation]], in which a living or deceased donor's organ is [[Organ transplant|transplanted]] into a person with a failing organ. The transplantation of larger solid organs often requires [[immunosuppression]] to prevent [[Transplant rejection|organ rejection]] or [[graft-versus-host disease]]. |
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There is considerable interest throughout the world in creating [[ |
There is considerable interest throughout the world in creating [[Tissue engineering|laboratory-grown]] or [[artificial organ]]s.{{uncited|date=February 2018}} |
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==History== |
==History== |
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[[File:View of Viscera Page 82.jpg|thumb|right|Human viscera]] |
[[File:View of Viscera Page 82.jpg|thumb|right|Human viscera]] |
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{{expandsection|date=February 2018}} |
{{expandsection|date=February 2018}} |
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The English word "organ" dates back to the twelfth century, in reference to any musical instrument. By the late 14th century, the musical term's meaning had narrowed to refer specifically to the [[Organ (music)|keyboard-based instrument]]. At the same time, a second meaning arose, in reference to a "body part adapted to a certain function".<ref>{{cite web |title=organ (n.) |url=https://www.etymonline.com/word/organism#etymonline_v_7139 |publisher=[[Online Etymology Dictionary]] |accessdate=22 March 2019}}</ref> |
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⚫ | Plant organs are made from tissue composed of different types of tissue. When three or more organs are present, it is called an organ system.<ref>{{Cite news|url=https://biologydictionary.net/organ-system/|title=Organ System - Definition and Examples {{!}} Biology Dictionary|date=2016-10-31|work=Biology Dictionary|access-date=2018-02-10|language=en-US}}</ref> |
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⚫ | The adjective ''[[ |
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⚫ | The adjective ''[[wikt:visceral|visceral]]'', also ''[[splanchnic]]'', is used for anything pertaining to the internal organs. Historically, viscera of animals were examined by [[Rome|Roman]] pagan [[priest]]s like the [[haruspices]] or the [[augur]]s in order to divine the future by their shape, dimensions or other factors. This practice remains an important ritual in some remote, tribal societies. |
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The term "visceral" is contrasted with the term "{{linktext|parietal}}", meaning "of or relating to the wall of a body part, [[Body cavity|organ or cavity]]"<ref>{{cite web|url=https://team.inria.fr/parietal/|title=Parietal – Learning brain structure, function and variability from neuroimaging data.|website=team.inria.fr|language=en-US|access-date=2018-02-10}}</ref> The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.{{fact|date=May 2015}} |
The term "visceral" is contrasted with the term "{{linktext|parietal}}", meaning "of or relating to the wall of a body part, [[Body cavity|organ or cavity]]"<ref>{{cite web|url=https://team.inria.fr/parietal/|title=Parietal – Learning brain structure, function and variability from neuroimaging data.|website=team.inria.fr|language=en-US|access-date=2018-02-10}}</ref> The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.{{fact|date=May 2015}} |
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===Antiquity=== |
===Antiquity=== |
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[[Aristotle]] used the word frequently in his philosophy, both to describe the organs of plants or animals (e.g. the roots of a tree, the heart or liver of an animal), and to describe more abstract "parts" of an interconnected whole (e.g. his logical works, taken as a whole, are referred to as the "[[organon]]"). |
[[Aristotle]] used the word frequently in his philosophy, both to describe the organs of plants or animals (e.g. the roots of a tree, the heart or liver of an animal), and to describe more abstract "parts" of an interconnected whole (e.g. his logical works, taken as a whole, are referred to as the "[[organon]]").<ref>{{cite web |last1=Lennox |first1=James |title=Aristotle's Biology |url=https://plato.stanford.edu/entries/aristotle-biology/ |website=Plato |publisher=Stanford University |accessdate=23 March 2019 |archivedate=15 Feb 2006 |date=31 Jan 2017 |quote=Section 2: Aristotle's Philosophy of Science}}</ref> |
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Some alchemists (e.g. [[Paracelsus]]) adopted the [[Hermetic Qabalah]] assignment between the seven vital organs and the seven [[classical planets]] as follows:<ref name="BallParacelsus">Philip Ball, ''The Devil's Doctor: Paracelsus and the World of Renaissance Magic and Science'', {{ISBN|978-0-09-945787-9}}{{pn|date=May 2015}}</ref> |
Some alchemists (e.g. [[Paracelsus]]) adopted the [[Hermetic Qabalah]] assignment between the seven vital organs and the seven [[classical planets]] as follows:<ref name="BallParacelsus">Philip Ball, ''The Devil's Doctor: Paracelsus and the World of Renaissance Magic and Science'', {{ISBN|978-0-09-945787-9}}{{pn|date=May 2015}}</ref> |
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===Modern times=== |
===Modern times=== |
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{{anchor|Modern times}} |
{{anchor|Modern times}} |
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The variations in [[natural language]] definitions of what constitutes an organ, their degree of precision, and the variations in how they map to [[ontology (information science)|ontologies]] and [[taxonomy for search engines|taxonomies]] in [[information science]] (for example, to count how many organs exist in a typical human body) are topics explored by writer Carl Engelking of [[Discover (magazine)|''Discover'' magazine]] in 2017 as he analyzed the [[science journalism]] coverage of the evolving scientific understanding of the [[mesentery]].<ref name="Engelking_2017-01-06">{{Citation |last=Engelking |first=Carl |date=2017-01-06 |title=We got the mesentery news all wrong |work=The Crux (a [[group blog]] by Discover writers) |url= http://blogs.discovermagazine.com/crux/2017/01/06/got-mesentery-news-wrong/ |doi= |postscript=.}}</ref> He explored a challenge now faced by anatomists: as human understanding of [[ontology]] generally (that is, how things are defined, and how the relationship of one thing to another is defined) meets [[applied ontology]] and [[ontology engineering]], unification of varying views is in higher demand.<ref name="Engelking_2017-01-06"/> However, such unification always faces [[epistemology|epistemologic]] frontiers, as humans can only declare computer ontologies with certainty and finality to the extent that their own cognitive [[taxonomy (general)|taxonomy]] (that is, science's understanding of the universe) is certain and final. For example, the fact that the tissues of the mesentery are continuous was something that was simply not known for sure until it was demonstrated with [[microscopy]].<ref name="CoffeyO'Leary2016">{{cite journal|last1=Coffey|first1=J Calvin|last2=O'Leary|first2=D Peter|title=The mesentery: structure, function, and role in disease|journal=The Lancet Gastroenterology & Hepatology|volume=1|issue=3|year=2016|pages=238–247|doi=10.1016/S2468-1253(16)30026-7}}</ref> Because humans cannot predict all future scientific discoveries, they cannot build a unified ontology that is totally certain and will never again change. However, one of the points made by an anatomist interviewed by Engelking is that, finality aside, much more could be done even now to [[knowledge representation and reasoning|represent existing human knowledge more clearly for computing purposes]]. |
The variations in [[natural language]] definitions of what constitutes an organ, their degree of precision, and the variations in how they map to [[ontology (information science)|ontologies]] and [[taxonomy for search engines|taxonomies]] in [[information science]] (for example, to count how many organs exist in a typical human body) are topics explored by writer Carl Engelking of [[Discover (magazine)|''Discover'' magazine]] in 2017 as he analyzed the [[science journalism]] coverage of the evolving scientific understanding of the [[mesentery]].<ref name="Engelking_2017-01-06">{{Citation |last=Engelking |first=Carl |date=2017-01-06 |title=We got the mesentery news all wrong |work=The Crux (a [[group blog]] by Discover writers) |url= http://blogs.discovermagazine.com/crux/2017/01/06/got-mesentery-news-wrong/ |doi= |postscript=.}}</ref> He explored a challenge now faced by anatomists: as human understanding of [[ontology]] generally (that is, how things are defined, and how the relationship of one thing to another is defined) meets [[applied ontology]] and [[ontology engineering]], unification of varying views is in higher demand.<ref name="Engelking_2017-01-06"/> However, such unification always faces [[epistemology|epistemologic]] frontiers, as humans can only declare computer ontologies with certainty and finality to the extent that their own cognitive [[taxonomy (general)|taxonomy]] (that is, science's understanding of the universe) is certain and final. For example, the fact that the tissues of the mesentery are continuous was something that was simply not known for sure until it was demonstrated with [[microscopy]].<ref name="CoffeyO'Leary2016">{{cite journal|last1=Coffey|first1=J Calvin|last2=O'Leary|first2=D Peter|title=The mesentery: structure, function, and role in disease|journal=The Lancet Gastroenterology & Hepatology|volume=1|issue=3|year=2016|pages=238–247|doi=10.1016/S2468-1253(16)30026-7}}</ref> Because humans cannot predict all future scientific discoveries, they cannot build a unified [[ontology]] that is totally certain and will never again change. However, one of the points made by an anatomist interviewed by Engelking is that, finality aside, much more could be done even now to [[knowledge representation and reasoning|represent existing human knowledge more clearly for computing purposes]]. |
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===Organ Procedures=== |
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Beginning in the 20th century<ref name="Organ Gov">{{cite web |title=Timeline of Historical Events and Significant Milestones |url=https://www.organdonor.gov/about/facts-terms/history.html |website=Organ Donor Government Web |accessdate=19 March 2019}}</ref> transplants began to occur as scientists knew more about the anatomy of organs. These came later in time as procedures were often dangerous and difficult.<ref>https://www.britannica.com/science/transplant-surgery#ref368668</ref> |
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==Origin and evolution== |
==Origin and evolution== |
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The organ level of organisation in [[animal]]s can be first detected in [[flatworm]]s and the more derived [[phylum|phyla]]. The less-advanced [[taxon|taxa]] (like ''[[Trichoplax|Placozoa]]'', ''[[Sponge]]s'' and ''[[Radiata]]'') do not show consolidation of their tissues into organs. |
The organ level of organisation in [[animal]]s can be first detected in [[flatworm]]s and the more derived [[phylum|phyla]]. The less-advanced [[taxon|taxa]] (like ''[[Trichoplax|Placozoa]]'', ''[[Sponge]]s'' and ''[[Radiata]]'') do not show consolidation of their tissues into organs. |
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More complex animals are composed of different organs, which have been evolving over time. For example, the liver evolved in the stem [[Vertebrate|vertebrates]] more than 500 million years ago, while the gut and brain are even more ancient, arising in the ancestor of vertebrates, insects, and worms more than 600 million years ago. |
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Given the ancient origin of most vertebrate organs, researchers have looked for model systems, where organs have evolved more recently, and ideally have evolved multiple times independently. An outstanding model for this kind of research is the [[placentation|placenta]], which has evolved more than 100 times independently in vertebrates, has evolved relatively recently in some lineages, and exists in intermediate forms in extant taxa.<ref name="Griffith">{{cite journal|last1=Griffith|first1=Oliver W.|last2=Wagner|first2=G?nter P.|title=The placenta as a model for understanding the origin and evolution of vertebrate organs|journal=Nature Ecology & Evolution|date=23 March 2017|volume=1|issue=4|page=0072|doi=10.1038/s41559-017-0072}}</ref> Studies on the evolution of the placenta have identified a variety of genetic and physiological processes that contribute to the origin and evolution of organs, these include the re-purposing of existing animal tissues, the acquisition of new functional properties by these tissues, and novel interactions of distinct tissue types.<ref name="Griffith"/> |
Given the ancient origin of most vertebrate organs, researchers have looked for model systems, where organs have evolved more recently, and ideally have evolved multiple times independently. An outstanding model for this kind of research is the [[placentation|placenta]], which has evolved more than 100 times independently in vertebrates, has evolved relatively recently in some lineages, and exists in intermediate forms in extant taxa.<ref name="Griffith">{{cite journal|last1=Griffith|first1=Oliver W.|last2=Wagner|first2=G?nter P.|title=The placenta as a model for understanding the origin and evolution of vertebrate organs|journal=Nature Ecology & Evolution|date=23 March 2017|volume=1|issue=4|page=0072|doi=10.1038/s41559-017-0072}}</ref> Studies on the evolution of the placenta have identified a variety of genetic and physiological processes that contribute to the origin and evolution of organs, these include the re-purposing of existing animal tissues, the acquisition of new functional properties by these tissues, and novel interactions of distinct tissue types.<ref name="Griffith"/> |
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{{Organ systems}} |
{{Organ systems}} |
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{{Composition (Biology)}} |
{{Composition (Biology)}} |
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[[Category:Levels of organization (Biology)]] |
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[[Category:Organ systems| ]] |
[[Category:Organ systems| ]] |
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[[Category:Organs (anatomy)| ]] |
[[Category:Organs (anatomy)| ]] |