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{{Short description|Tube attached to the intestine}}
{{Infobox Anatomy |
{{Infobox anatomy
Name = Vermiform appendix |
Latin = appendix vermiformis | | Name = Appendix
| Image = Tractus intestinalis appendix vermiformis.svg
GraySubject = 249 |
| Caption = Appendix with surrounding structures
GrayPage = 1179 |
Image = Gray536.png | | Width =200
| Precursor = ]
Caption = Arteries of cecum and vermiform appendix. (Appendix visible at lower right, labeled as 'vermiform process'). |
| System = ]
Image2 = Stomach_colon_rectum_diagram.gif |
| Artery = ]
Caption2 = Normal location of the appendix relative to other organs of the digestive system (anterior view). |
System = ] | | Vein = ]
MeshName = Appendix | | Nerve =
| Lymph =
MeshNumber = A03.556.124.526.209.290 |
|Image2=Appendix locations.svg|Caption2=Variations of the appendix}}
DorlandsPre = a_54 |
DorlandsSuf = 12147735 |
}}
In ], the '''vermiform appendix''' (or '''appendix''', pl. ''appendixes'' or ''appendices'') is a blind ended tube connected to the ] ('caecum' in British English). It develops embryologically from the cecum. The term vermiform comes from Latin and means "wormlike in appearance". The cecum is the first pouch-like structure of the colon. The appendix is near the junction of the
small intestines and large intestines.


The '''appendix''' ({{plural form}}: '''appendices''' or '''appendixes'''; also '''vermiform appendix'''; '''cecal''' (or '''caecal''', '''cæcal''') '''appendix'''; '''vermix'''; or '''vermiform process''') is a finger-like, blind-ended tube connected to the ], from which it ].
==Size and location==
The appendix averages 10 cm in length, but can range from 2-20 cm. The diameter of the appendix is usually less than 7-8 mm. The longest appendix ever removed was that of a ]i man on ], ], at ], ], measuring 23.5 cm (9.2 in) in length. <ref name="record"></ref>


The cecum is a pouch-like structure of the ], located at the junction of the ] and the large intestines. The term "]" comes from ] and means "worm-shaped". The appendix was once considered a ], but this view has changed since the early 2000s.<ref>{{cite journal|vauthors=Kooij IA, Sahami S, Meijer SL, Buskens CJ, Te Velde AA|date=October 2016|title=The immunology of the vermiform appendix: a review of the literature|journal=]|volume=186|issue=1|pages=1–9|doi=10.1111/cei.12821|pmc=5011360|pmid=27271818}}</ref><ref>{{Cite journal |last1=Smith |first1=H. F. |last2=Fisher |first2=R. E. |last3=Everett |first3=M. L. |last4=Thomas |first4=A. D. |last5=Randal Bollinger |first5=R. |last6=Parker |first6=W. |date=2009 |title=Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix |journal=Journal of Evolutionary Biology |language=en |volume=22 |issue=10 |pages=1984–1999 |doi=10.1111/j.1420-9101.2009.01809.x|pmid=19678866 |doi-access=free }}</ref> Research suggests that the appendix may serve an important purpose as a reservoir for beneficial ].
While the base of the appendix is at a fairly constant location, the location of the tip of the appendix can vary from being retrocaecal to being in the ] to being ]. In most people, the appendix is located at the lower right quadrant of the abdomen. In people with ], the appendix may be located in the lower left side.


==Function== == Structure ==
The human appendix averages {{convert|9|cm|in|abbr=on}} in length, ranging from {{convert|5|to|35|cm|in|abbr=on}}. The diameter of the appendix is {{convert|6|mm|in|abbr=on}}, and more than {{convert|6|mm|in|abbr=on}} is considered a thickened or inflamed appendix. The longest appendix ever removed was {{convert|26|cm|in|abbr=on}} long.<ref name="record">{{cite web |url=https://www.guinnessworldrecords.com/world-records/largest-appendix-removed |title=Largest appendix removed |date=26 August 2006 |publisher=] |access-date=22 May 2017 |url-status=live |archive-url=https://web.archive.org/web/20201126014839/https://www.guinnessworldrecords.com/world-records/largest-appendix-removed |archive-date=26 November 2020}}</ref> The appendix is usually located in the lower right ] of the ], near the right ]. The base of the appendix is located {{convert|2|cm|in|abbr=on}} beneath the ] that separates the large intestine from the small intestine. Its position within the abdomen corresponds to a point on the surface known as ].
Currently, the function of the appendix, if any, remains controversial in the field of human ].


The appendix is connected to the ] in the lower region of the ], by a short region of the ] known as the ].<ref name="auto">{{cite journal |last1=Golalipour |first1=M.J. |last2=Arya |first2=B. |last3=Jahanshahi |first3=M. |last4=Azarhoosh |first4=R. |date=2003 |title=Anatomical Variations Of Vermiform Appendix In South-East Caspian Sea (Gorgan-IRAN) |url=https://medind.nic.in/jae/t03/i2/jaet03i2p141.pdf |journal=J. Anat. Soc. India |access-date=1 October 2014 |url-status=live |archive-url=https://web.archive.org/web/20200711120812/https://medind.nic.in/jae/t03/i2/jaet03i2p141.pdf |archive-date=11 July 2020}}</ref>
There have been cases of people who have been found, usually on ] or ], to have a ] absence of their appendix. There have been no reports of impaired immune or ] function in these people.


===Variation===
One explanation has been that the appendix is a remnant of an earlier function, with no current purpose. (Note, however, that the ], which only recently (around 1960) was found to produce important chemicals such as ], was once similarly considered a ].)
Some identical twins—known as ]—can have a ], a ] with the appendix located in the lower left quadrant of the abdomen instead of the lower right.<ref>{{cite web|url=https://www.multiplesofamerica.org/research/unusual-types-of-twins/|title=Unusual Types of Twins|publisher=Multiples of America|url-status=dead|archive-url=https://web.archive.org/web/20140502001856/http://www.nomotc.org/index.php?option=com_content&task=view&id=59&Itemid=54|archive-date=2 May 2014|access-date=30 April 2014}}</ref><ref>{{cite journal | vauthors = Gedda L, Sciacca A, Brenci G, Villatico S, Bonanni G, Gueli N, Talone C | title = Situs viscerum specularis in monozygotic twins | journal = Acta Geneticae Medicae et Gemellologiae | volume = 33 | issue = 1 | pages = 81–5 | year = 1984 | pmid = 6540028 | doi = 10.1017/S0001566000007546 | doi-access = free }}</ref> ] may also cause displacement of the appendix to the left side.


While the base of the appendix is typically located {{convert|2|cm|in|abbr=on}} below the ], the tip of the appendix can be variably located—in the ], outside the ] or behind the cecum.<ref name="Surgery">{{Cite book|author=Paterson-Brown, S. |chapter= 15. The acute abdomen and intestinal obstruction |editor1=Parks, Rowan W. |editor2=Garden, O. James |editor3=Carter, David John |editor4=Bradbury, Andrew W. |editor5=Forsythe, John L. R. |title=Principles and practice of surgery |publisher= Churchill Livingstone |location=Edinburgh |year=2007 |isbn=978-0-443-10157-1 |edition=5th}}</ref> The prevalence of the different positions varies amongst populations with the retrocecal position being most common in ] and ], with 67.3% and 58.3% occurrence respectively, in comparison to ] and ] where the pelvic position is most common, with 55.8% and 57.7% occurrence respectively.<ref>{{cite journal | vauthors = Clegg-Lamptey JN, Armah H, Naaeder SB, Adu-Aryee NA | title = Position and susceptibility to inflammation of vermiform appendix in Accra, Ghana | journal = East African Medical Journal | volume = 83 | issue = 12 | pages = 670–3 | date = December 2006 | pmid = 17685212 | doi = 10.4314/eamj.v83i12.9498 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Bakheit MA, Warille AA | title = Anomalies of the vermiform appendix and prevalence of acute appendicitis in Khartoum | journal = East African Medical Journal | volume = 76 | issue = 6 | pages = 338–40 | date = June 1999 | pmid = 10750522 }}</ref><ref>{{cite journal|vauthors=Ghorbani A, Forouzesh M, Kazemifar AM|year=2014|title=Variation in Anatomical Position of Vermiform Appendix among Iranian Population: An Old Issue Which Has Not Lost Its Importance|journal=]|volume=2014|pages=313575|doi=10.1155/2014/313575|pmc=4176911|pmid=25295193|doi-access=free}}</ref><ref>{{cite journal | vauthors = Denjalić A, Delić J, Delić-Custendil S, Muminagić S | title = | language = bs | journal = Medicinski Arhiv | volume = 63 | issue = 2 | pages = 100–1 | year = 2009 | pmid = 19537667 }}</ref>
==Diseases==
The most common diseases of the appendix (in humans) are ] and ].


In very rare cases, the appendix may not be present at all (] for suspected appendicitis have given a frequency of 1 in 100,000).<ref>{{cite journal | vauthors = Zetina-Mejía CA, Alvarez-Cosío JE, Quillo-Olvera J | title = Congenital absence of the cecal appendix. Case report | journal = Cirugia y Cirujanos | volume = 77 | issue = 5 | pages = 407–10 | year = 2009 | pmid = 19944032 }}</ref>
An operation to remove the appendix is an ] (also appendectomy).


Sometimes there is a semi-circular fold of ] at the opening of the appendix. This ''valve of the vermiform appendix'' is also called ] valve.<ref name="auto"/>
Appendix don't have a function, they only used to when humans used to eat grass, but since we stopped our appendix have just been in our bodies, doing othing, except getting infected and removed!


==References== ==Functions==
<references/>
<!-- Dead note "agenesis1": {{cite journal | author=Lima M, ''et al'' | title=Agenesis of the appendix vermiformis | journal=Pediatr Med Chir | year=2003 | pages=370-2 | volume=25 | issue=5 | id=PMID 15058839}} -->
<!-- Dead note "agenesis2": {{cite journal | author=Greenberg SL, ''et al'' | title=Congenital absence of the vermiform appendix | journal=ANZ J Surg | year=2003 | pages=166-7 | volume=73 | issue=3 | id=PMID 12608987}} -->


===Maintaining gut flora===
==External links==
]]]
* -- ] argument that the appendix is vestigial
*
{{digestive system}}


Although it has been long accepted that the immune tissue surrounding the appendix and elsewhere in the gut—called ]—carries out a number of important functions, explanations were lacking for the distinctive shape of the appendix and its apparent lack of specific importance and function as judged by an absence of side effects following ].<ref name="PBD4thEd">{{Cite book |author1=Kumar, Vinay |author2=Robbins, Stanley L. |author3=Cotran, Ramzi S. |title=Robbins' pathologic basis of disease |publisher=Saunders |location=Philadelphia |year=1989 |pages= |isbn=978-0-7216-2302-3 |edition=4th |url-access=registration |url=https://archive.org/details/robbinspathologi00robb/page/902 }}</ref> Therefore, the notion that the appendix is only ] became widely held.
]
]


William Parker, Randy Bollinger, and colleagues at ] proposed in 2007 that the appendix serves as a haven for useful ] when illness flushes the bacteria from the rest of the intestines.<ref name=health>{{cite news |agency=] |date=5 October 2007 |title=Scientists may have found appendix's purpose |url=http://www.nbcnews.com/id/21153898/ |url-status=dead |work=] |archive-url=https://web.archive.org/web/20200204135004/http://www.nbcnews.com/id/21153898 |archive-date=4 February 2020 |access-date=24 August 2019}}</ref><ref name="JTBpaper">{{cite journal | vauthors = Randal Bollinger R, Barbas AS, Bush EL, Lin SS, Parker W | title = Biofilms in the large bowel suggest an apparent function of the human vermiform appendix | journal = Journal of Theoretical Biology | volume = 249 | issue = 4 | pages = 826–31 | date = December 2007 | pmid = 17936308 | doi = 10.1016/j.jtbi.2007.08.032 | bibcode = 2007JThBi.249..826R }}</ref> This proposition is based on an understanding that emerged by the early 2000s of how the immune system supports the growth of beneficial ],<ref>{{cite journal | vauthors = Sonnenburg JL, Angenent LT, Gordon JI | title = Getting a grip on things: how do communities of bacterial symbionts become established in our intestine? | journal = ] | volume = 5 | issue = 6 | pages = 569–73 | date = June 2004 | pmid = 15164016 | doi = 10.1038/ni1079 | s2cid = 25672527 }}</ref><ref>{{cite journal |author1=Everett M.L. |author2=Palestrant D. |author3=Miller S.E. |author4=Bollinger R.R. |author5=Parker W. |title=Immune exclusion and immune inclusion: a new model of host-bacterial interactions in the gut |journal=Clinical and Applied Immunology Reviews |volume=4 |pages=321–32 |year=2004|doi=10.1016/j.cair.2004.03.001|issue=5}}</ref> in combination with many well-known features of the appendix, including its architecture, its location just below the normal one-way flow of food and germs in the large intestine, and its association with copious amounts of immune tissue.
]

]
Research performed at ] showed that individuals without an appendix were four times as likely to have a recurrence of ].<ref>{{cite web |url=https://blogs.scientificamerican.com/guest-blog/2012/01/02/your-appendix-could-save-your-life/ |title=Your Appendix Could Save Your Life |last=Dunn |first=Rob |date=January 2, 2012 |publisher=] |access-date=22 December 2016 |url-status=live |archive-url=https://web.archive.org/web/20201111234503/https://blogs.scientificamerican.com/guest-blog/your-appendix-could-save-your-life/ |archive-date=11 November 2020}}</ref> The appendix, therefore, may act as a "safe house" for beneficial bacteria.<ref name="health" /> This reservoir of bacteria could then serve to repopulate the ] in the ] following a bout of ] or ] or to boost it following a milder gastrointestinal illness.<ref name="JTBpaper"/>
]

]
===Immune and lymphatic systems===
]
The appendix has been identified as an important component of mammalian ], particularly ]-mediated immune responses and ] derived ]s. This structure helps in the proper movement and removal of waste matter in the digestive system, contains lymphatic vessels that regulate pathogens, and lastly, might even produce early defences that prevent deadly diseases. Additionally, it is thought that this may provide more immune defences from invading pathogens and getting the lymphatic system's B and T cells to fight the viruses and bacteria that infect that portion of the bowel and training them so that immune responses are targeted and more able to reliably and less dangerously fight off pathogens.<ref>{{cite journal | vauthors = Zahid A | title = The vermiform appendix: not a useless organ | journal = Journal of the College of Physicians and Surgeons--Pakistan | volume = 14 | issue = 4 | pages = 256–8 | date = April 2004 | pmid = 15228837 }}</ref> In addition, there are different immune cells called ]s that function in the gut in order to help the appendix maintain digestive health.<ref>{{cite journal|display-authors=6|vauthors=Rankin LC, Girard-Madoux MJ, Seillet C, Mielke LA, Kerdiles Y, Fenis A, Wieduwild E, Putoczki T, Mondot S, Lantz O, Demon D, Papenfuss AT, Smyth GK, Lamkanfi M, Carotta S, Renauld JC, Shi W, Carpentier S, Soos T, Arendt C, Ugolini S, Huntington ND, Belz GT, Vivier E|date=February 2016|title=Complementarity and redundancy of IL-22-producing innate lymphoid cells|journal=]|volume=17|issue=2|pages=179–86|doi=10.1038/ni.3332|pmc=4720992|pmid=26595889}}</ref>
]

]
Research also shows a positive correlation between the existence of the appendix and the concentration of cecal lymphoid tissue, which supports the suggestion that not only does the appendix evolve as a complex with the cecum but also has major immune benefits.<ref>{{cite journal | vauthors = Smith H, Parker W, Kotze S, Laurin M| title = Morphological evolution of the mammalian cecum and cecal appendix | journal = Comptes Rendus Palevol| volume = 16 | issue = 1 | pages = 39–57 | date = September 2016 |doi=10.1016/j.crpv.2016.06.001| url = https://zenodo.org/record/894682 | doi-access = free }}</ref>
]

]
==Clinical significance==
]
]
]

]
Common ]s of the appendix (in humans) are ] and ] tumors (appendiceal carcinoid).<ref>{{cite journal |url=https://pubmed.ncbi.nlm.nih.gov/15807474/ |title=Miscellaneous conditions of the appendix |author=<!--Not stated--> |journal=Seminars in Diagnostic Pathology |year=2004 |volume=21 |issue=2 |pages=151–63 |publisher=] |access-date=30 December 2020 |doi=10.1053/j.semdp.2004.11.006|pmid=15807474 }}</ref> ] accounts for about 1 in 200 of all gastrointestinal malignancies. In rare cases, ] are also present.<ref>{{cite web|access-date=2020-12-30 |url=https://www.rightdiagnosis.com/a/appendix_disorders/stats.htm |title=Statistics about Appendix disorder |work=rightdiagnosis.com |url-status=dead |archive-url=https://web.archive.org/web/20191016210240/https://www.rightdiagnosis.com/a/appendix_disorders/stats.htm |archive-date=2019-10-16}}</ref>
]

]
===Appendicitis===
]
{{Main|Appendicitis}}
] is a condition characterized by ] of the appendix. Pain often begins in the center of the abdomen, corresponding to the appendix's development as part of the embryonic ]. This pain is typically a dull, poorly localized, ] pain.<ref name="Biology 92-98">{{Cite book|author=Miller R., Kenneth |author2=Levine, Joseph |title=Biology |publisher=] |year=2002 |isbn=978-0-13-050730-3 |pages=92–98}}</ref>

As the inflammation progresses, the pain begins to localize more clearly to the right lower quadrant, as the ] becomes inflamed. This peritoneal inflammation, or ], results in ] (pain upon removal of pressure rather than application of pressure). In particular, it presents at ], 1/3 of the way along a line drawn from the ] to the ]. Typically, point (skin) pain is not present until the ] is inflamed, as well. Fever and an immune system response are also characteristic of appendicitis.<ref name="Biology 92-98"/> Other signs and symptoms may include ] and vomiting, low-grade fever that may get worse, ] or ], abdominal bloating, or ].<ref name=Mayo-Appendicitis>{{cite web |url=https://www.mayoclinic.org/diseases-conditions/appendicitis/symptoms-causes/syc-20369543 |title=Appendicitis - Symptoms and causes - Mayo Clinic |author=<!--Not stated--> |website=mayoclinic.org |publisher=] |access-date=29 December 2020 |url-status=live |archive-url=https://web.archive.org/web/20201125012725/https://www.mayoclinic.org/diseases-conditions/appendicitis/symptoms-causes/syc-20369543 |archive-date=25 November 2020 }}</ref>

Appendicitis usually requires the removal of the inflamed appendix, in an ] either by ] or ]. Untreated, the appendix may rupture, leading to ], followed by ], and, if still untreated, death.<ref name="Biology 92-98"/>

===Surgery===

{{Main|Appendectomy}}

The surgical removal of the appendix is called an ]. This removal is normally performed as an emergency procedure when the patient is suffering from ] appendicitis. In the absence of surgical facilities, ] ] are used to delay or avoid the onset of ]. In some cases, the appendicitis resolves completely; more often, an inflammatory mass forms around the appendix. This is a relative ] to surgery.

The appendix is also used for the construction of an efferent urinary conduit, in an operation known as the ],<ref name=mingin>{{cite journal | vauthors = Mingin GC, Baskin LS | title = Surgical management of the neurogenic bladder and bowel | journal = International Braz J Urol | volume = 29 | issue = 1 | pages = 53–61 | year = 2003 | pmid = 15745470 | doi = 10.1590/S1677-55382003000100012 | url = http://www.brazjurol.com.br/january_february_2003/Baskin_ing_53_61.htm | doi-access = free }}</ref> in people with a ].

The appendix is also used as a means to access the colon in children with paralysed bowels or major rectal sphincter problems. The appendix is brought out to the skin surface and the child/parent can then attach a catheter and easily wash out the colon (via normal defaecation) using an appropriate solution.<ref>{{cite web|url=http://www.healthpoint.co.nz/default,169125.sm;jsessionid=1CD66A058B10550C51041E477C8E7075|title=Wellington Children's Hospital : Caring for an ACE or Chait Tube : Healthpoint|access-date=22 December 2016|archive-date=16 October 2019|archive-url=https://web.archive.org/web/20191016171448/https://www.healthpoint.co.nz/public/paediatrics/wellington-childrens-hospital-paediatric/caring-for-an-ace-or-chait-tube/|url-status=dead}}</ref>

==History==
] suggested that the appendix was mainly used by earlier hominids for digesting fibrous vegetation, then evolved to take on a new purpose over time. The very long cecum of some herbivorous animals, such as in the ] or the ], appears to support this hypothesis. The koala's cecum enables it to host bacteria that specifically help to break down cellulose. Human ancestors may have also relied upon this system when they lived on a diet rich in foliage.

As people began to eat more easily digested foods, they may have become less reliant on cellulose-rich plants for energy. As the cecum became less necessary for digestion, mutations that were previously deleterious (and would have hindered evolutionary progress) were no longer important, so the mutations survived. It is suggested that these ]s became more frequent and the cecum continued to shrink. After millions of years, the once-necessary cecum degraded to be the appendix of modern humans.<ref name="DescentOfMan">{{Cite book |last=Darwin |first=Charles |author-link=Charles Darwin |title=The Descent of Man, and Selection in Relation to Sex |title-link=The Descent of Man, and Selection in Relation to Sex |publisher=John Murray |year=1871 |location=London |chapter=Jim's Jesus}}</ref>

Dr. Heather F. Smith of ] and colleagues explained:

<blockquote>Recently ... improved understanding of gut immunity has merged with current thinking in biological and medical science, pointing to an apparent function of the mammalian cecal appendix as a safe-house for symbiotic gut microbes, preserving the flora during times of gastrointestinal infection in societies without modern medicine. This function is potentially a selective force for the evolution and maintenance of the appendix.
Three morphotypes of cecal-appendices can be described among mammals based primarily on the shape of the cecum: a distinct appendix branching from a rounded or sac-like cecum (as in many primate species), an appendix located at the apex of a long and voluminous cecum (as in the rabbit, greater glider and Cape dune mole rat), and an appendix in the absence of a pronounced cecum (as in the wombat). In addition, long narrow appendix-like structures are found in mammals that either lack an apparent cecum (as in monotremes) or lack a distinct junction between the cecum and appendix-like structure (as in the koala). A cecal appendix has evolved independently at least twice, and apparently represents yet another example of convergence in morphology between Australian marsupials and placentals in the rest of the world. Although the appendix has apparently been lost by numerous species, it has also been maintained for more than 80 million years in at least one clade.<ref name=SEAL09>{{cite journal | vauthors = Smith HF, Fisher RE, Everett ML, Thomas AD, Bollinger RR, Parker W | title = Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix | journal = Journal of Evolutionary Biology | volume = 22 | issue = 10 | pages = 1984–99 | date = October 2009 | pmid = 19678866 | doi = 10.1111/j.1420-9101.2009.01809.x | s2cid = 6112969 | doi-access = free }}</ref></blockquote>

In a 2013 paper, the appendix was found to have independently evolved in different animals at least 32 times (and perhaps as many as 38 times) and to have been lost no more than six times over the course of history.<ref name = SEAL13>{{cite journal | author1 = Smith H. F. |author2=Parker W. |author3=Kotzé, S. H. |author4=Laurin, M. | year = 2013 | title = Multiple independent appearances of the cecal appendix in mammalian evolution and an investigation of related ecological and anatomical factors | journal = Comptes Rendus Palevol | volume = 12| issue = 6| pages = 339–354| doi = 10.1016/j.crpv.2012.12.001 |bibcode=2013CRPal..12..339S | doi-access = free }}</ref> A more recent study using similar methods on an updated database yielded similar, though less spectacular results, with at least 29 gains and at the most 12 losses (all of which were ambiguous), and this is still significantly asymmetrical.<ref name = SEAL17>{{cite journal | author1 = Smith H. F. |author2=Parker W. |author3=Kotzé, S. H. |author4=Laurin, M. | year = 2017 | title = Morphological evolution of the mammalian cecum and cecal appendix | journal = Comptes Rendus Palevol | volume = 11| issue = 1| pages = 39–57| doi = 10.1016/j.crpv.2016.06.001 |bibcode=2017CRPal..16...39S | doi-access = free }}</ref>

This suggests that the cecal appendix has a selective advantage in many situations and argues strongly against its vestigial nature. Given that this organ may have a selective advantage in numerous situations, it appears to be associated with greater maximal longevity, for a given body mass.<ref name="Collard et al. 2021">{{cite journal |last1=Collard |first1=Maxime K. |last2=Bardin |first2=Jérémie |last3=Laurin |first3=Michel |last4=Ogier‐Denis |first4=Eric |title=The cecal appendix is correlated with greater maximal longevity in mammals |journal=Journal of Anatomy |date=November 2021 |volume=239 |issue=5 |pages=1157–1169 |doi=10.1111/joa.13501 |url=https://doi.org/10.1111/joa.13501 |language=en |issn=0021-8782|pmc=8546507 }}</ref> For example, in a 2023 study, the protective functions conferred against diarrhea were observed in young primates.<ref>{{Cite journal |last1=Collard |first1=Maxime K. |last2=Bardin |first2=Jérémie |last3=Marquet |first3=Bertille |last4=Laurin |first4=Michel |last5=Ogier-Denis |first5=Éric |date=2023-09-23 |title=Correlation between the presence of a cecal appendix and reduced diarrhea severity in primates: new insights into the presumed function of the appendix |journal=Scientific Reports |language=en |volume=13 |issue=1 |pages=15897 |doi=10.1038/s41598-023-43070-5 |issn=2045-2322 |pmc=10517977 |pmid=37741857|bibcode=2023NatSR..1315897C }}</ref> This complex evolutionary history of the appendix, along with a great heterogeneity in its evolutionary rate in various taxa, suggests that it is a recurrent trait.<ref name = LEAL11>{{cite journal | vauthors = Laurin M, Everett ML, Parker W | title = The cecal appendix: one more immune component with a function disturbed by post-industrial culture | journal = Anatomical Record | volume = 294 | issue = 4 | pages = 567–79 | date = April 2011 | pmid = 21370495 | doi = 10.1002/ar.21357 | s2cid = 3237168 }}</ref>

Such a function may be useful in a culture lacking modern sanitation and healthcare practice, where ] may be prevalent. Current ] data on the cause of death in developing countries collected by the ] in 2001 show that acute diarrhea is now the fourth leading cause of disease-related death in developing countries (data summarized by the ]). Two of the other leading causes of death are expected to have exerted limited or no selection pressure.<ref>{{Cite web |date=21 August 2009 |orig-date=20 August 2009 |title=Evolution of the Appendix: A Biological 'Remnant' No More |url=http://www.dukehealth.org/health_library/news/evolution_of_the_appendix_a_biological_remnant_no_more |url-status=dead |archive-url=https://web.archive.org/web/20120726030646/http://www.dukehealth.org/health_library/news/evolution_of_the_appendix_a_biological_remnant_no_more |archive-date=2012-07-26 |access-date= |website=Duke Medicine News and Communications}}</ref>

==Additional images==
<gallery>
File:Ultrasonography of a normal appendix, annotated.jpg|] showing a normal appendix between the ] and the abdominal wall
File:Blausen 0043 Appendix Child.png|Illustration depicting the location of the appendix in a child
File:Stomach colon rectum diagram-en.svg|Normal location of the appendix relative to other organs of the digestive system (frontal view)
File:Appendix vermiformis.jpg|Vermiform appendix
File:Appendixcancer.jpg|Mucinous ] of the appendix tip
File:Enterobius - very low mag.jpg|] of the appendix with '']'' with ]
File:Micrograph of entry point of appendicular arteries.jpg|Micrograph of entry point of ] (arrows at level of inner muscular layer), not to be confused with a perforation.
</gallery>

== See also ==
* ]
* ], a detached efferent duct of the epididymis
* ], a vestigial remnant of the Müllerian duct
* ], one of several small pouches of fat on the peritoneum along the colon and rectum
** ], a sac that extends from the laryngeal ventricle
* ], the portion of the mesentery that connects the ileum to the vermiform appendix

== References ==
{{Reflist|2}}

== Further reading ==
* —2007 ] article
* {{SUNYAnatomyLabs|37|12|01|02}}—"Abdominal Cavity: The Cecum and the Vermiform Appendix"
* —] argument that the appendix is vestigial
* {{cite journal|vauthors=Smith HF, Fisher RE, Everett ML, Thomas AD, Bollinger RR, Parker W|title=Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix|journal=]|volume=22|issue=10|pages=1984–99|date=October 2009|pmid=19678866|doi=10.1111/j.1420-9101.2009.01809.x|s2cid=6112969|doi-access=free}}
* Cho, Jinny (August 27, 2009). . '']'' (]). (News article on the above journal article.)

== External links ==
* {{Commons category inline|Vermiform appendix|Appendix (anatomy)}}

{{Digestive tract}}
{{Authority control}}

{{DEFAULTSORT:Vermiform Appendix}}
]
]

Latest revision as of 15:45, 6 November 2024

Tube attached to the intestine
Appendix
Appendix with surrounding structures
Variations of the appendix
Details
PrecursorMidgut
SystemDigestive system
ArteryAppendicular artery
VeinAppendicular vein
Identifiers
MeSHD001065
TA98A05.7.02.007
TA22976
FMA14542
Anatomical terminology[edit on Wikidata]

The appendix (pl.: appendices or appendixes; also vermiform appendix; cecal (or caecal, cæcal) appendix; vermix; or vermiform process) is a finger-like, blind-ended tube connected to the cecum, from which it develops in the embryo.

The cecum is a pouch-like structure of the large intestine, located at the junction of the small and the large intestines. The term "vermiform" comes from Latin and means "worm-shaped". The appendix was once considered a vestigial organ, but this view has changed since the early 2000s. Research suggests that the appendix may serve an important purpose as a reservoir for beneficial gut bacteria.

Structure

The human appendix averages 9 cm (3.5 in) in length, ranging from 5 to 35 cm (2.0 to 13.8 in). The diameter of the appendix is 6 mm (0.24 in), and more than 6 mm (0.24 in) is considered a thickened or inflamed appendix. The longest appendix ever removed was 26 cm (10 in) long. The appendix is usually located in the lower right quadrant of the abdomen, near the right hip bone. The base of the appendix is located 2 cm (0.79 in) beneath the ileocecal valve that separates the large intestine from the small intestine. Its position within the abdomen corresponds to a point on the surface known as McBurney's point.

The appendix is connected to the mesentery in the lower region of the ileum, by a short region of the mesocolon known as the mesoappendix.

Variation

Some identical twins—known as mirror image twins—can have a mirror-imaged anatomy, a congenital condition with the appendix located in the lower left quadrant of the abdomen instead of the lower right. Intestinal malrotation may also cause displacement of the appendix to the left side.

While the base of the appendix is typically located 2 cm (0.79 in) below the ileocecal valve, the tip of the appendix can be variably located—in the pelvis, outside the peritoneum or behind the cecum. The prevalence of the different positions varies amongst populations with the retrocecal position being most common in Ghana and Sudan, with 67.3% and 58.3% occurrence respectively, in comparison to Iran and Bosnia where the pelvic position is most common, with 55.8% and 57.7% occurrence respectively.

In very rare cases, the appendix may not be present at all (laparotomies for suspected appendicitis have given a frequency of 1 in 100,000).

Sometimes there is a semi-circular fold of mucous membrane at the opening of the appendix. This valve of the vermiform appendix is also called Gerlach's valve.

Functions

Maintaining gut flora

A possible function of the human appendix is a "safe house" for beneficial bacteria in the recovery from diarrhea

Although it has been long accepted that the immune tissue surrounding the appendix and elsewhere in the gut—called gut-associated lymphoid tissue—carries out a number of important functions, explanations were lacking for the distinctive shape of the appendix and its apparent lack of specific importance and function as judged by an absence of side effects following its removal. Therefore, the notion that the appendix is only vestigial became widely held.

William Parker, Randy Bollinger, and colleagues at Duke University proposed in 2007 that the appendix serves as a haven for useful bacteria when illness flushes the bacteria from the rest of the intestines. This proposition is based on an understanding that emerged by the early 2000s of how the immune system supports the growth of beneficial intestinal bacteria, in combination with many well-known features of the appendix, including its architecture, its location just below the normal one-way flow of food and germs in the large intestine, and its association with copious amounts of immune tissue.

Research performed at Winthrop–University Hospital showed that individuals without an appendix were four times as likely to have a recurrence of Clostridioides difficile colitis. The appendix, therefore, may act as a "safe house" for beneficial bacteria. This reservoir of bacteria could then serve to repopulate the gut flora in the digestive system following a bout of dysentery or cholera or to boost it following a milder gastrointestinal illness.

Immune and lymphatic systems

The appendix has been identified as an important component of mammalian mucosal immune function, particularly B cell-mediated immune responses and extrathymically derived T cells. This structure helps in the proper movement and removal of waste matter in the digestive system, contains lymphatic vessels that regulate pathogens, and lastly, might even produce early defences that prevent deadly diseases. Additionally, it is thought that this may provide more immune defences from invading pathogens and getting the lymphatic system's B and T cells to fight the viruses and bacteria that infect that portion of the bowel and training them so that immune responses are targeted and more able to reliably and less dangerously fight off pathogens. In addition, there are different immune cells called innate lymphoid cells that function in the gut in order to help the appendix maintain digestive health.

Research also shows a positive correlation between the existence of the appendix and the concentration of cecal lymphoid tissue, which supports the suggestion that not only does the appendix evolve as a complex with the cecum but also has major immune benefits.

Clinical significance

An appendiceal carcinoid tumor

Common diseases of the appendix (in humans) are appendicitis and carcinoid tumors (appendiceal carcinoid). Appendix cancer accounts for about 1 in 200 of all gastrointestinal malignancies. In rare cases, adenomas are also present.

Appendicitis

Main article: Appendicitis

Appendicitis is a condition characterized by inflammation of the appendix. Pain often begins in the center of the abdomen, corresponding to the appendix's development as part of the embryonic midgut. This pain is typically a dull, poorly localized, visceral pain.

As the inflammation progresses, the pain begins to localize more clearly to the right lower quadrant, as the peritoneum becomes inflamed. This peritoneal inflammation, or peritonitis, results in rebound tenderness (pain upon removal of pressure rather than application of pressure). In particular, it presents at McBurney's point, 1/3 of the way along a line drawn from the anterior superior iliac spine to the umbilicus. Typically, point (skin) pain is not present until the parietal peritoneum is inflamed, as well. Fever and an immune system response are also characteristic of appendicitis. Other signs and symptoms may include nausea and vomiting, low-grade fever that may get worse, constipation or diarrhea, abdominal bloating, or flatulence.

Appendicitis usually requires the removal of the inflamed appendix, in an appendectomy either by laparotomy or laparoscopy. Untreated, the appendix may rupture, leading to peritonitis, followed by shock, and, if still untreated, death.

Surgery

Main article: Appendectomy

The surgical removal of the appendix is called an appendectomy. This removal is normally performed as an emergency procedure when the patient is suffering from acute appendicitis. In the absence of surgical facilities, intravenous antibiotics are used to delay or avoid the onset of sepsis. In some cases, the appendicitis resolves completely; more often, an inflammatory mass forms around the appendix. This is a relative contraindication to surgery.

The appendix is also used for the construction of an efferent urinary conduit, in an operation known as the Mitrofanoff procedure, in people with a neurogenic bladder.

The appendix is also used as a means to access the colon in children with paralysed bowels or major rectal sphincter problems. The appendix is brought out to the skin surface and the child/parent can then attach a catheter and easily wash out the colon (via normal defaecation) using an appropriate solution.

History

Charles Darwin suggested that the appendix was mainly used by earlier hominids for digesting fibrous vegetation, then evolved to take on a new purpose over time. The very long cecum of some herbivorous animals, such as in the horse or the koala, appears to support this hypothesis. The koala's cecum enables it to host bacteria that specifically help to break down cellulose. Human ancestors may have also relied upon this system when they lived on a diet rich in foliage.

As people began to eat more easily digested foods, they may have become less reliant on cellulose-rich plants for energy. As the cecum became less necessary for digestion, mutations that were previously deleterious (and would have hindered evolutionary progress) were no longer important, so the mutations survived. It is suggested that these alleles became more frequent and the cecum continued to shrink. After millions of years, the once-necessary cecum degraded to be the appendix of modern humans.

Dr. Heather F. Smith of Midwestern University and colleagues explained:

Recently ... improved understanding of gut immunity has merged with current thinking in biological and medical science, pointing to an apparent function of the mammalian cecal appendix as a safe-house for symbiotic gut microbes, preserving the flora during times of gastrointestinal infection in societies without modern medicine. This function is potentially a selective force for the evolution and maintenance of the appendix. Three morphotypes of cecal-appendices can be described among mammals based primarily on the shape of the cecum: a distinct appendix branching from a rounded or sac-like cecum (as in many primate species), an appendix located at the apex of a long and voluminous cecum (as in the rabbit, greater glider and Cape dune mole rat), and an appendix in the absence of a pronounced cecum (as in the wombat). In addition, long narrow appendix-like structures are found in mammals that either lack an apparent cecum (as in monotremes) or lack a distinct junction between the cecum and appendix-like structure (as in the koala). A cecal appendix has evolved independently at least twice, and apparently represents yet another example of convergence in morphology between Australian marsupials and placentals in the rest of the world. Although the appendix has apparently been lost by numerous species, it has also been maintained for more than 80 million years in at least one clade.

In a 2013 paper, the appendix was found to have independently evolved in different animals at least 32 times (and perhaps as many as 38 times) and to have been lost no more than six times over the course of history. A more recent study using similar methods on an updated database yielded similar, though less spectacular results, with at least 29 gains and at the most 12 losses (all of which were ambiguous), and this is still significantly asymmetrical.

This suggests that the cecal appendix has a selective advantage in many situations and argues strongly against its vestigial nature. Given that this organ may have a selective advantage in numerous situations, it appears to be associated with greater maximal longevity, for a given body mass. For example, in a 2023 study, the protective functions conferred against diarrhea were observed in young primates. This complex evolutionary history of the appendix, along with a great heterogeneity in its evolutionary rate in various taxa, suggests that it is a recurrent trait.

Such a function may be useful in a culture lacking modern sanitation and healthcare practice, where diarrhea may be prevalent. Current epidemiological data on the cause of death in developing countries collected by the World Health Organization in 2001 show that acute diarrhea is now the fourth leading cause of disease-related death in developing countries (data summarized by the Bill and Melinda Gates Foundation). Two of the other leading causes of death are expected to have exerted limited or no selection pressure.

Additional images

See also

References

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  2. Smith, H. F.; Fisher, R. E.; Everett, M. L.; Thomas, A. D.; Randal Bollinger, R.; Parker, W. (2009). "Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix". Journal of Evolutionary Biology. 22 (10): 1984–1999. doi:10.1111/j.1420-9101.2009.01809.x. PMID 19678866.
  3. "Largest appendix removed". Guinness World Records. 26 August 2006. Archived from the original on 26 November 2020. Retrieved 22 May 2017.
  4. ^ Golalipour, M.J.; Arya, B.; Jahanshahi, M.; Azarhoosh, R. (2003). "Anatomical Variations Of Vermiform Appendix In South-East Caspian Sea (Gorgan-IRAN)" (PDF). J. Anat. Soc. India. Archived (PDF) from the original on 11 July 2020. Retrieved 1 October 2014.
  5. "Unusual Types of Twins". Multiples of America. Archived from the original on 2 May 2014. Retrieved 30 April 2014.
  6. Gedda L, Sciacca A, Brenci G, Villatico S, Bonanni G, Gueli N, Talone C (1984). "Situs viscerum specularis in monozygotic twins". Acta Geneticae Medicae et Gemellologiae. 33 (1): 81–5. doi:10.1017/S0001566000007546. PMID 6540028.
  7. Paterson-Brown, S. (2007). "15. The acute abdomen and intestinal obstruction". In Parks, Rowan W.; Garden, O. James; Carter, David John; Bradbury, Andrew W.; Forsythe, John L. R. (eds.). Principles and practice of surgery (5th ed.). Edinburgh: Churchill Livingstone. ISBN 978-0-443-10157-1.
  8. Clegg-Lamptey JN, Armah H, Naaeder SB, Adu-Aryee NA (December 2006). "Position and susceptibility to inflammation of vermiform appendix in Accra, Ghana". East African Medical Journal. 83 (12): 670–3. doi:10.4314/eamj.v83i12.9498. PMID 17685212.
  9. Bakheit MA, Warille AA (June 1999). "Anomalies of the vermiform appendix and prevalence of acute appendicitis in Khartoum". East African Medical Journal. 76 (6): 338–40. PMID 10750522.
  10. Ghorbani A, Forouzesh M, Kazemifar AM (2014). "Variation in Anatomical Position of Vermiform Appendix among Iranian Population: An Old Issue Which Has Not Lost Its Importance". Anatomy Research International. 2014: 313575. doi:10.1155/2014/313575. PMC 4176911. PMID 25295193.
  11. Denjalić A, Delić J, Delić-Custendil S, Muminagić S (2009). "". Medicinski Arhiv (in Bosnian). 63 (2): 100–1. PMID 19537667.
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  17. Everett M.L.; Palestrant D.; Miller S.E.; Bollinger R.R.; Parker W. (2004). "Immune exclusion and immune inclusion: a new model of host-bacterial interactions in the gut". Clinical and Applied Immunology Reviews. 4 (5): 321–32. doi:10.1016/j.cair.2004.03.001.
  18. Dunn, Rob (January 2, 2012). "Your Appendix Could Save Your Life". Scientific American. Archived from the original on 11 November 2020. Retrieved 22 December 2016.
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  27. "Wellington Children's Hospital : Caring for an ACE or Chait Tube : Healthpoint". Archived from the original on 16 October 2019. Retrieved 22 December 2016.
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  30. Smith H. F.; Parker W.; Kotzé, S. H.; Laurin, M. (2013). "Multiple independent appearances of the cecal appendix in mammalian evolution and an investigation of related ecological and anatomical factors". Comptes Rendus Palevol. 12 (6): 339–354. Bibcode:2013CRPal..12..339S. doi:10.1016/j.crpv.2012.12.001.
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Further reading

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