آپاندیس زائدهای کوچک و انگشتی شکل است که از روده بزرگ منشعب میشود. این زائده به انتهای بنبست در سکوم (روده کور) متصل است. در جدار این عضو بافت لنفاوی فراوانی موجود است. طول آپاندیس بین ۲ تا ۲۰ سانتیمتر متغیر است و قطر آن نیز بین ۶ تا ۸ میلیمتر است. عفونت و التهاب در آن منجر به آپاندیسیت میشود.
آپاندیس عضو وستیجیال محسوب میشود. کارکرد ویژهای در بدن انسان ندارد و باقیماندهیی از نیاکان انسان است که طی فرگشت از بین نرفته است.
برخی از دانشمندان به تازگی نظریاتی ابراز داشتهاند که نشان از کارایی این عضو دارد. نتایج تحقیقات ساینتیفیک آمریکن حاکی از آن است که آپاندیس در نوزادان به تولید هورمون و در افراد بزرگسال به تولید پادگنهای (آنتیژنهای) مفید برای ایمنی بدن و مبارزه با بیماری کمک میکند. همچنین تحقیقات دیگری نشان میدهد که آپاندیس نقش عمدهای در سیستم ایمنی بدن دارد. بافتهای لنفاوی جداره آپاندیس با حس کردن میکروبهای موجود در مواد زاید در حال دفع از بدن، نوع خوب یا بد میکروبها را تشخیص داده و به بانک حافظهای سیستم ایمنی بدن اجازه میدهند تا در مقابله (و دفع) میکروبهای مضر و ساختن میکروبهای مفید برنامه ریزی کرده و فعال گردد. آمار مرگ و میر در اثر اسهال مزمن در کشورهای فقیر یا در حال رشد نشان داده که آپاندیس سالم با ذخیره باکتریهای خوب در خود میتواند سیستم گوارشی افراد را پس از آلوده شدن به میکروبهای مضر باعث اسهال، با بازگشت میکروبهای مفید بهبود داده و از آمار مرگ و میر بکاهد.همچنین در بعضی آدم ها وقتی آپاندیس آلوده شده به عفونت مزمن میشود و آن را از بدن جدا میکنند باعث سفت شدن شکم و روده راست میشود و هموروئید را ایجاد میکنند وچربی خون در اثر باکتریهای آزاد شده موجب چربی خون میشود و خون آلوده میشود
علل عفونت آپاندیس[ویرایش]
وقتی غذا از طریق مری به معده و روده بزرگ می رسد باکتریهایی که روده نصفی از آن ها رابه خود جذب میکند به داخل خون می روند و اما آپاندیس آن باکتریها را از پوست خارجی آپاندیس به خود جذب میکنند این باکتریها زیاد میشود سپس باعث عفونت آپاندیسیت می شود.[پیوند مرده]
For other uses, see Appendix (disambiguation).
The appendix (or vermiform appendix; also cecal [or caecal] appendix; vermix; or vermiform process) is a blind-ended tube connected to the cecum, from which it develops embryologically. The cecum is a pouchlike structure of the colon, located at the junction of the small and the large intestines.
The human appendix averages 9 cm in length but can range from 2 to 20 cm. The diameter of the appendix is usually between 7 and 8 mm. The longest appendix ever removed was 26 cm long; it was removed from a patient in Zagreb, Croatia. 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 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.
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. Intestinal malrotation may also cause displacement of the appendix to the left side.
While the base of the appendix is at a fairly constant location—2 cm 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.
Maintaining gut flora
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 those bacteria from the rest of the intestines. This proposal 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 more likely to have a recurrence of Clostridium difficile colitis. The appendix, therefore, may act as a "safe house" for commensal ("good") bacteria. This reservoir of gut flora could then serve to repopulate the digestive system following a bout of dysentery or cholera.
Immune and lymphatic system
The appendix has more recently 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 a different kind of immune cell called innate lymphoid cells function in the gut, which help the appendix maintain digestive health.
The human appendix had been proposed to be a vestigial structure, a structure that has lost all or most of its original function, or that has evolved to take on a new function. The suggestion was that it is the shrunken remnant of the cecum thought to have been present in a remote ancestor of humans. This notion is still widely held. A 2013 study, however, refutes the idea of an inverse relationship between cecum size and appendix size and presence. Ceca, which occur in the digestive tracts of many herbivores (e.g. ox, horse), house mutualistic bacteria and ingested small stones that help animals digest the cellulose molecules found in plants.
It is widely present in euarchontoglires (a superorder of mammals that includes rodents and primates) and has also evolved independently in the diprotodont marsupials, monotremes, and is highly diverse in size and shape.
A possible scenario for the progression from a fully functional cecum to the current human appendix was put forth by Charles Darwin. He suggested that the appendix was used for digesting leaves as primates. It may be a vestigial organ of ancient humans that has degraded to nearly nothing of its original purpose, or evolved to take on a new purpose over the course of evolution. The very long cecum of some herbivorous animals, such as found in the horse or the koala, appears to support this theory. 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.
The most 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.
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.
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.
The surgical removal of the vermiform 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 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.
Dr. Heather F. Smith of Midwestern University and colleagues explained:
In a more recent paper, the appendix was found to have evolved at least 32 times (and perhaps as many as 38 times) and to have been lost no more than six times. This suggests that the cecal appendix has a selective advantage in many situations and argues strongly against its vestigial nature. 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 developed 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.