View source for Organ (biology)

{{short description|Collection of tissues with similar functions}}
{{Redirect-multi|2|Organs|Viscera}}
{{Infobox anatomy
| Name        = Organ
| Image    = Internal organs.png
| Caption  = Many of the internal organs of the [[human body]]
| Width       =
| Latin        = organum
| Greek       = oργανο
| System      = [[Organ system]]s
| Artery      =
| Vein        =
| Nerve       =
| Lymph       =
}}

In a multicellular [[organism]], an '''organ''' is a collection of [[Tissue (biology)|tissues]] joined in a structural unit to serve a common [[Function (biology)|function]].<ref>{{Cite book |last1=Widmaier |first1=E P |title=Vander's Human Physiology |last2=Raff |first2=H |last3=Strang |first3=KT |year=2014 |publisher=McGraw-Hill Higher Education |isbn=978-0-07-128366-3 |edition=12th}}{{page needed|date=May 2015}}</ref> In the [[biological organization|hierarchy of life]], an organ lies between [[Tissue (biology)|tissue]] and an [[organ system]]. Tissues are formed from same type [[Cell (biology)|cells]] to act together in a function. Tissues of different types combine to form an organ which has a specific function. The [[Gastrointestinal tract|intestinal wall]] for example is formed by [[epithelial tissue]] and [[smooth muscle tissue]].<ref name="Kent">{{cite book |last1=Kent |first1=Michael |title=Advanced biology |date=2000 |publisher=Oxford University Press |location=Oxford |isbn=0-19-914195-9 |page=81}}</ref> 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.

An organ's tissues can be broadly categorized as [[parenchyma]], the functional tissue, and [[stroma (tissue)|stroma]], the structural tissue with supportive, connective, or [[ancillary]] functions. For example, the [[gland]]'s tissue that makes the [[hormone]]s is the [[parenchyma]], whereas the stroma includes the [[nerve tissue|nerves]] that innervate the parenchyma, the [[blood vessel]]s that oxygenate and nourish it and carry away its [[Metabolism|metabolic]] wastes, and the [[connective tissue]]s that provide a suitable place for it to be situated and anchored. The main tissues that make up an organ tend to have common [[embryology|embryologic]] origins, such as arising from the same [[germ layer]]. Organs exist in most multicellular [[organism]]s. In [[unicellular organism|single-celled organisms]] such as members of the [[eukaryotes]], 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 |via=Wikibooks, open books for an open world |url=https://en.wikibooks.org/wiki/Botany/Plant_structure |website=en.wikibooks.org |language=en |access-date=2018-02-06 |archive-date=2018-02-07 |archive-url=https://web.archive.org/web/20180207122257/https://en.wikibooks.org/wiki/Botany/Plant_structure |url-status=live }}</ref>

The number of organs in any organism depends on the definition used. There are approximately 79 organs in the human body; the precise count is debated.<ref>{{Cite news |date=2017 |title=New organ named in digestive system |language=en-GB |work=BBC News |url=https://www.bbc.com/news/health-38506708 |access-date=2018-02-05 |archive-date=2018-03-24 |archive-url=https://web.archive.org/web/20180324023635/http://www.bbc.com/news/health-38506708 |url-status=live }}</ref>

==Animals==
{{See also|List of organs of the human body | Biological system}}
[[File:Leber Schaf.jpg|thumb|The [[liver]] and [[gallbladder]] of a [[sheep]]]]
Except for [[placozoa]]ns, [[multicellular]] [[animal]]s including humans have a variety of [[organ system]]s. These specific systems are widely studied in [[human anatomy]]. The functions of these 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.
* [[Cardiovascular system]]: pumping and channeling [[blood]] to and from the [[human body|body]] and [[lung]]s with [[heart]], [[blood]] and [[blood vessel]]s.
* [[Digestion|Digestive system]]: [[digestion]] and processing food with [[salivary gland]]s, [[esophagus]], [[stomach]], [[liver]], [[gallbladder]], [[pancreas]], [[intestine]]s, [[Colon (anatomy)|colon]], [[mesentery]], [[rectum]] and [[anus]].
* [[Endocrine system]]: communication within the body using [[hormone]]s made by [[endocrine gland]]s such as the [[hypothalamus]], [[pituitary]] gland, [[pineal body]] or pineal gland, [[thyroid]], [[parathyroid]]s and [[adrenal]]s, i.e., adrenal glands.
* [[Excretory system]]: [[Kidney (vertebrates)|kidneys]], [[ureter]]s, [[urinary bladder|bladder]] and [[urethra]] involved in fluid balance, [[electrolyte]] balance and excretion of [[urine]].
* [[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]].
* [[Integumentary system]]: [[skin]], [[hair]] and [[nail (anatomy)|nails]] of [[mammal]]s. Also [[scale (anatomy)|scales]] of [[fish]], [[reptile]]s, and [[bird]]s, and [[feather]]s of birds.
* [[Muscular system]]: movement with [[muscle]]s.
* [[Nervous system]]: collecting, transferring and processing information with [[brain]], [[spinal cord]] and [[nerve]]s.
* [[Reproductive system]]: the [[sex organ]]s, such as [[ovary|ovaries]], [[oviduct]]s, [[uterus]], [[vulva]], [[vagina]], [[testicle]]s, [[vasa deferentia]], [[seminal vesicle]]s, [[prostate]] and [[penis]].
* [[Respiratory system]]: the organs used for [[breathing]], the [[pharynx]], [[larynx]], [[Vertebrate trachea|trachea]], [[bronchi]], [[lung]]s and [[thoracic diaphragm|diaphragm]].
* [[Skeleton|Skeletal system]]: structural support and protection with [[bone]]s, [[cartilage]], [[ligament]]s and [[tendon]]s.

===Viscera===
[[File:Internal Organs of the Human Body from The Household Physician, 1905 (6404030777).jpg|thumb|1905 diagram of the internal organs of human body]]{{Split portions|date=April 2025|Innervation of the pelvic viscera|List of pelvic organs|discuss=Organ (biology)#Proposed splits|section=y}}
In the study of [[anatomy]], '''viscera''' ({{singular}}: '''viscus''') refers to the '''internal organs''' of the [[abdominal cavity|abdominal]], [[thoracic cavity|thoracic]], and [[Pelvic cavity|pelvic cavities]].<ref name="Bell">{{cite web |last1=Bell |first1=Daniel J. |title=Viscera {{!}} Radiology Reference Article  |url=https://radiopaedia.org/articles/viscera?lang=gb |website=Radiopaedia.org|date=5 April 2021 }}</ref> The abdominal organs may be classified as '''solid organs''' or '''hollow organs'''. The solid organs are the [[liver]], [[pancreas]], [[spleen]], [[kidney]]s, and [[adrenal gland]]s. The hollow organs of the abdomen are the [[stomach]], [[intestines]], [[gallbladder]], [[bladder]], and [[rectum]].<ref>{{cite web |last1=Bell |first1=Daniel J. |title=Solid and hollow abdominal viscera {{!}} Radiology Reference Article  |url=https://radiopaedia.org/articles/solid-and-hollow-abdominal-viscera?lang=gb |website=Radiopaedia.org |date=25 July 2017 |access-date=24 November 2021}}</ref> In the [[thoracic cavity]], the [[heart]] is a hollow, muscular organ.<ref>{{cite web |title=Biology of the Heart – Heart and Blood Vessel Disorders |url=https://www.msdmanuals.com/en-gb/home/heart-and-blood-vessel-disorders/biology-of-the-heart-and-blood-vessels/biology-of-the-heart |website=MSD Manual Consumer Version |access-date=24 November 2021}}</ref>  [[Splanchnology]] is the study of the viscera.<ref name="MW">{{cite web |title=Medical Definition of SPLANCHNOLOGY |url=https://www.merriam-webster.com/medical/splanchnology |website=Merriam-Webster |access-date=25 November 2021 |language=en}}</ref> 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 name="Inria">{{Cite web |title=Parietal – Learning brain structure, function and variability from neuroimaging data. |url=https://team.inria.fr/parietal/ |access-date=2018-02-10 |website=team.inria.fr |language=en-US |archive-date=2018-02-10 |archive-url=https://web.archive.org/web/20180210235039/https://team.inria.fr/parietal/ |url-status=live }}</ref> The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.<ref name="Thoracic cavity">{{Cite web |title=Thoracic cavity |url=https://www.amboss.com/us/knowledge/Thoracic_cavity |access-date=8 September 2019 |website=Amboss |archive-date=21 July 2019 |archive-url=https://web.archive.org/web/20190721192732/https://www.amboss.com/us/knowledge/Thoracic_cavity |url-status=live }}</ref>

===Origin and evolution===
[[File:Origin of major organs on the animal phylogeny.jpg|thumb|Relationship of major animal lineages with indication of how long ago these animals shared a common ancestor. On the left, important organs are shown, which allows us to determine how long ago these may have evolved.]]
The organ level of organisation in [[animal]]s can be first detected in [[flatworm]]s and the more derived [[phylum|phyla]], i.e. the [[bilateria]]ns. The less-advanced [[taxon|taxa]] (i.e. ''[[Placozoa]]'', ''[[Porifera]]'', ''[[Ctenophora]]'' and ''[[Cnidaria]]'') do not show unification of their tissues into organs.

More complex animals are composed of different organs, which have evolved over time. For example, the liver and heart evolved in the [[chordate]]s about 550–500 million years ago, while the gut and brain are even more ancient, arising in the ancestor of vertebrates, insects, [[Mollusca|molluscs]], and worms about 700–650 million years ago.

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 [[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=Günter P. |date=23 March 2017 |title=The placenta as a model for understanding the origin and evolution of vertebral organs |journal=Nature Ecology & Evolution |volume=1 |issue=4 |page=0072 |doi=10.1038/s41559-017-0072 |pmid=28812655 |bibcode=2017NatEE...1...72G |s2cid=32213223}}</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" />

==Plants==  <!-- courtesy note per [[WP:RSECT]]: [[Plant organ]] and [[Plant organs]] redirect here -->
{{See also| Plant morphology | Plant anatomy | Plant physiology}}
[[Image:Red Hibiscus in Chennai during Spring.JPG|thumb|right|The flower is the angiosperm's reproductive organ. This ''[[Hibiscus]]'' flower is [[Hermaphroditic (botany)|hermaphroditic]], and it contains [[stamen]] and [[Gynoecium|pistils]].]]
[[Image:Equisetum braunii (strobilus), Portland, Oregon.jpg|thumb|right|Strobilus of ''[[Equisetum telmateia]]'']]
The study of plant organs is covered in [[plant morphology]]. 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]].{{Citation needed|date=August 2021}} 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. Common organ system designations in plants include 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 |title=The Plant Body {{!}} Boundless Biology |url=https://courses.lumenlearning.com/boundless-biology/chapter/the-plant-body/ |access-date=2019-03-19 |website=courses.lumenlearning.com |archive-date=2019-01-21 |archive-url=https://web.archive.org/web/20190121024801/https://courses.lumenlearning.com/boundless-biology/chapter/the-plant-body/ |url-status=live }}</ref>

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]]).

==Society and culture==
Many societies have a system for [[organ donation]], in which a living or deceased donor's organ are [[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]].

There is considerable interest throughout the world in creating [[Tissue engineering|laboratory-grown]] or [[artificial organ]]s.{{citation needed|date=February 2018}}

===Organ transplants===
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 |access-date=19 March 2019 |website=Organ Donor Government Web |archive-date=19 January 2019 |archive-url=https://web.archive.org/web/20190119164138/https://www.organdonor.gov/about/facts-terms/history.html |url-status=live }}</ref> [[Organ transplantation|organ transplants]] began to take place as scientists knew more about the anatomy of organs. These came later in time as procedures were often dangerous and difficult.<ref>{{Cite web |title=transplant &#124; Definition, Types, & Rejection |url=https://www.britannica.com/science/transplant-surgery |website=Encyclopedia Britannica |access-date=2019-03-19 |archive-date=2019-03-27 |archive-url=https://web.archive.org/web/20190327170406/https://www.britannica.com/science/transplant-surgery |url-status=live }}</ref> Both the source and method of obtaining the organ to transplant are major ethical issues to consider, and because organs as resources for transplant are always more limited than demand for them, various notions of justice, including [[distributive justice]], are developed in the ethical analysis. This situation continues as long as transplantation relies upon organ donors rather than technological innovation, testing, and industrial manufacturing.{{Citation needed|date=May 2021}}

Animal donor organs and tissue have been subjects of study since the 1960s, and some xenotransplant tissues, particularly heart valves, have been commonly utilized. Xenotransplant has the potential to address the critical shortage in organ grafts. The science behind [xenotransplant] trials has advanced considerably and more human clinical trials utilizing porcine xenografts are quickly approaching.<ref name="Xenotransplantation">{{Cite journal |last1=Carrier |first1=A. N. |last2=Verma |first2=A. |last3=Mohiuddin |first3=M. |last4=Pascual |first4=M. |last5=Muller |first5=Y. D. |last6=Longchamp |first6=A. |last7=Bhati |first7=C. |last8=Buhler |first8=L. H. |last9=Maluf |first9=D. G. |last10=Meier |first10=R. P. H. |title=Xenotransplantation: A New Era |journal=Frontiers in Immunology |date=2022 |volume=13 |article-number=900594 |doi=10.3389/fimmu.2022.900594 |doi-access=free |pmid=35757701 |pmc=9218200 }}{{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref>

==History==
[[File:View of Viscera Page 82.jpg|thumb|right|Human viscera]]
{{expand section|date=February 2018}}
The English word "organ" dates back to the twelfth century, referring to any musical instrument.<ref>{{Cite web |date=26 October 2025 |title=Organ. |url=https://www.merriam-webster.com/dictionary/organ |access-date=29 October 2025 |website=Merriam-Webster Dictionary}}</ref> 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 encyclopedia |title=organ (n.) |encyclopedia=[[Online Etymology Dictionary]] |url=https://www.etymonline.com/word/organism#etymonline_v_7139 |access-date=22 March 2019 |archive-date=1 May 2019 |archive-url=https://web.archive.org/web/20190501171549/https://www.etymonline.com/word/organism#etymonline_v_7139 |url-status=live }}</ref>

Plant organs are made from tissue composed of different types of tissue. The three tissue types are ground, vascular, and dermal.<ref>{{Cite web |title=Plant Development I: Tissue differentiation and function |url=http://bio1520.biology.gatech.edu/growth-and-reproduction/plant-development-i-tissue-differentiation-and-function/ |access-date=8 September 2019 |website=Biology 1520 (Georgia Tech) |publisher=Georgia Tech |archive-date=3 September 2019 |archive-url=https://web.archive.org/web/20190903142732/http://bio1520.biology.gatech.edu/growth-and-reproduction/plant-development-i-tissue-differentiation-and-function/ |url-status=live }}</ref> When three or more organs are present, it is called an organ system.<ref>{{Cite news |date=2016-10-31 |title=Organ System – Definition and Examples {{!}} Biology Dictionary |language=en-US |work=Biology Dictionary |url=https://biologydictionary.net/organ-system/ |access-date=2018-02-10 |archive-date=2018-02-10 |archive-url=https://web.archive.org/web/20180210180610/https://biologydictionary.net/organ-system/ |url-status=live }}</ref>

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.<ref>{{Cite book |last=Dickie |first=Matthew W. |title=Magic and Magicians in the Greco-Roman World |date=2003 |publisher=Routledge |isbn=0-415-31129-2 |edition=1st |page=274}}</ref> This practice remains an important ritual in some remote, tribal societies.

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 name="Inria"/> The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.<ref name="Thoracic cavity"/>

===Antiquity===
[[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) because, in ancient Greek, the word '''organon''<nowiki/>' means 'tool', and Aristotle believed that the organs of the body were tools for us by means of which we can do things. For similar reasons, his logical works, taken as a whole, are referred to as the ''[[Organon]]'' because logic is a ''tool'' for philosophical thinking.<ref>{{Cite web |last=Lennox |first=James |date=31 Jan 2017 |title=Aristotle's Biology |url=https://plato.stanford.edu/entries/aristotle-biology/ |archive-date=7 May 2019 |access-date=23 March 2019 |website=Plato |publisher=Stanford University |quote=Section 2: Aristotle's Philosophy of Science |archive-url=https://web.archive.org/web/20190507040441/https://plato.stanford.edu/entries/aristotle-biology/ |url-status=live }}</ref> Earlier thinkers, such as those who wrote texts in the [[Hippocratic corpus]], generally did not believe that there were organs of the body but only different ''parts'' of the body.<ref>Gundert 1992: 465. Gundert, Beate. 1992. "Parts and Their Roles in Hippocratic Medicine," ''Isis'' 83: 453–65.</ref>

Some alchemists (e.g. [[Paracelsus]]) adopted the [[Hermetic Qabalah]] assignment between the seven vital organs and the seven [[classical planets]] as follows:
<ref>{{Cite book |last=Ball |first=Philip |title=The devil's doctor |date=2007 |publisher=Arrow |isbn=978-0-09-945787-9 |location=London |oclc=124919518 }}</ref>
{|class="wikitable"
|-
! '''Planet''' !! '''Organ'''
|-
|Sun||Heart
|-
|Moon||Brain
|-
|Mercury||Lungs
|-
|Venus||Kidneys
|-
|Mars||Gall bladder
|-
|Jupiter||Liver
|-
|Saturn||Spleen
|}

[[Chinese traditional medicine]] recognizes eleven organs, associated with the [[Wuxing (Chinese philosophy)|five Chinese traditional elements]] and with [[yin and yang]], as follows:

{|class="wikitable"
|-
! '''Element''' !! '''Yin/yang''' !! '''Organ'''
|-
| rowspan="2" | Wood
| yin
| liver
|-
| yang
| gall bladder
|-
| rowspan="2" | Fire
| yin
| heart
|-
| yang
| small intestine / [[san jiao]]
|-
| rowspan="2" | Earth
| yin
| spleen
|-
| yang
| stomach
|-
| rowspan="2" | Metal
| yin
| lungs
|-
| yang
| large intestine
|-
| rowspan="2" | Water
| yin
| kidneys
|-
| yang
| bladder
|}

The Chinese associated the five elements with the five planets (Jupiter, Mars, Venus, Saturn, and Mercury) similar to the way the classical planets were associated with different metals. The ''yin'' and ''yang'' distinction approximates the modern notion of solid and hollow organs.

==See also==
{{Commons category|Organ systems}}
* [[List of organs of the human body]]
* [[Organoid]]
* [[Organ-on-a-chip]]
* [[Situs inversus]]

==References==
{{reflist|2}}<ref>{{Cite web |date=26 October 2025 |title=Organ |url=https://www.merriam-webster.com/dictionary/organ}}</ref>

==External links==
* {{commons category-inline|Organs (anatomy)}}

{{Organ systems}}
{{Composition (Biology)}}

{{Authority control}}

[[Category:Levels of organization (Biology)]]
[[Category:Organ systems| ]]
[[Category:Organs (anatomy)| ]]