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lands within four tissue sections the cells have been stained to show a brown orange color if the cells produce the mitochondrial protein cytochrome c oxidase subunit i ccoi and the nuclei of the cells located at the outer edges of the cells lining the walls of the crypts are stained blue gray with haematoxylin panels a b were cut across the long axes of the crypts and panels c d were cut parallel to the long axes of the crypts in panel a the bar shows 100 μm and allows an estimate of the frequency of crypts in the colonic epithelium panel b includes three crypts in cross section each with one segment deficient for ccoi expression and at least one crypt on the right side undergoing fission into two crypts panel c shows on the left side a crypt fissioning into two crypts panel d shows typical small clusters of two and three ccoi deficient crypts the bar shows 50 μm the images were made from original photomicrographs but panels a b and d were also included in an article 29 and illustrations were published with creative commons attribution noncommercial license allowing re use the wall of the large intestine is lined with simple columnar epithelium with invaginations the invaginations are called the intestinal glands or colonic crypts micrograph of normal large instestinal crypts anatomy of normal large intestinal crypts the colon crypts are shaped like microscopic thick walled test tubes with a central hole down the length of the tube the crypt lumen four tissue sections are shown here two cut across the long axes of the crypts and two cut parallel to the long axes in these images the cells have been stained by immunohistochemistry to show a brown orange color if the cells produce a mitochondrial protein called cytochrome c oxidase subunit i ccoi the nuclei of the cells located at the outer edges of the cells lining the walls of the crypts are stained blue gray with haematoxylin as seen in panels c and d crypts are about 75 to about 110 cells long baker et al 30 found that the average crypt circumference is 23 cells thus by the images shown here there are an average of about 1 725 to 2 530 cells per colonic crypt nooteboom et al 31 measuring the number of cells in a small number of crypts reported a range of 1 500 to 4 900 cells per colonic crypt cells are produced at the crypt base and migrate upward along the crypt axis before being shed into the colonic lumen days later 30 there are 5 to 6 stem cells at the bases of the crypts 30 as estimated from the image in panel a there are about 100 colonic crypts per square millimeter of the colonic epithelium 32 since the average length of the human colon is 160 5 cm 11 and the average inner circumference of the colon is 6 2 cm 32 the inner surface epithelial area of the human colon has an average area of about 995 cm 2 which includes 9 950 000 close to 10 million crypts in the four tissue sections shown here many of the intestinal glands have cells with a mitochondrial dna mutation in the ccoi gene and appear mostly white with their main color being the blue gray staining of the nuclei as seen in panel b a portion of the stem cells of three crypts appear to have a mutation in ccoi so that 40 to 50 of the cells arising from those stem cells form a white segment in the cross cut area overall the percent of crypts deficient for ccoi is less than 1 before age 40 but then increases linearly with age 29 colonic crypts deficient for ccoi in women reaches on average 18 in women and 23 in men by 80 84 years of age 29 crypts of the colon can reproduce by fission as seen in panel c where a crypt is fissioning to form two crypts and in panel b where at least one crypt appears to be fissioning most crypts deficient in ccoi are in clusters of crypts clones of crypts with two or more ccoi deficient crypts adjacent to each other see panel d 29 mucosa edit about 150 of the many thousands of protein coding genes expressed in the large intestine some are specific to the mucous membrane in different regions and include ceacam7 33 function edit histological section the large intestine absorbs water and any remaining absorbable nutrients from the food before sending the indigestible matter to the rectum 34 the colon absorbs vitamins that are created by the colonic bacteria such as thiamine riboflavin and vitamin k 35 36 it also compacts feces and stores fecal matter in the rectum until it can be discharged via the anus in defecation the large intestine also secretes potassium and chloride recycling of various nutrients takes place in the colon examples include fermentation of carbohydrates short chain fatty acids and urea cycling 34 the appendix contains a small amount of mucosa associated lymphoid tissue which gives the appendix an undetermined role in immunity however the appendix is known to be important in fetal life as it contains endocrine cells that release biogenic amines and peptide hormones important for homeostasis during early growth and development 37 by the time chyme enters the large intestine the small intestine has absorbed nearly all digestible nutrients and approximately 90 of the ingested water based on volume measurements showing that only about 1 2 litres of fluid pass into the colon from a daily intestinal load of roughly 9 10 litres 38 39 indeed as demonstrated by the commonality of ileostomy procedures it is possible for many people to live without large portions of their large intestine or even without it completely at this point only some electrolytes like sodium magnesium and chloride are left as well as indigestible parts of ingested food e g a large part of ingested amylose starch which has been shielded from digestion heretofore and dietary fiber which is largely indigestible carbohydrate in either soluble or insoluble form as the chyme moves through the large intestine most of the remaining water is removed while the chyme is mixed with mucus and bacteria known as gut flora and becomes feces the ascending colon receives fecal material as a liquid the muscles of the colon then move the watery waste material forward and slowly absorb all the excess water causing the stools to gradually solidify as they move along into the descending colon 34 the bacteria break down some of the fiber for their own nourishment and create acetate propionate and butyrate as waste products which in turn are used by the cell lining of the colon for nourishment 40 no protein is made available in humans perhaps 10 of the undigested carbohydrate thus becomes available though this may vary with diet 41 in other animals including other apes and primates who have proportionally larger colons more is made available thus permitting a higher portion of plant material in the diet the large intestine produces no digestive enzymes chemical digestion is completed in the small intestine before the chyme reaches the large intestine the ph in the colon varies between 5 5 and 7 slightly acidic to neutral 34 standing gradient osmosis edit water absorption at the colon typically proceeds against a transmucosal osmotic pressure gradient the standing gradient osmosis is the reabsorption of water against the osmotic gradient in the intestines cells occupying the intestinal lining pump sodium ions into the intercellular space raising the osmolarity of the intercellular fluid this hypertonic fluid creates an osmotic pressure that drives water into the lateral intercellular spaces by osmosis via tight junctions and adjacent cells which then in turn moves across the basement membrane and into the capillaries while more sodium ions are pumped again into the intercellular fluid 42 although water travels down an osmotic gradient in each individual step overall water usually travels against the osmotic gradient due to the pumping of sodium ions into the intercellular fluid this allows the large intestine to absorb water despite the blood in capillaries being hypotonic compared to the fluid within the intestinal lumen gut flora edit main article gut microbiota the large intestine houses over 700 species of bacteria that perform a variety of functions as well as fungi protozoa and archaea species diversity varies by geography and diet 43 the microbes in a human distal gut often number in the vicinity of 100 trillion and can weigh around 200 grams 0 44 pounds this mass of mostly symbiotic microbes has recently been called the latest human organ to be discovered or in other words the forgotten organ 44 the large intestine absorbs some of the products formed by the bacteria inhabiting this region undigested polysaccharides fiber are metabolized to short chain fatty acids by bacteria in the large intestine and absorbed by passive diffusion the bicarbonate that the large intestine secretes helps to neutralize the increased acidity resulting from the formation of these fatty acids 45 these bacteria also produce large amounts of vitamins especially vitamin k and biotin a b vitamin for absorption into the blood although this source of vitamins in general provides only a small part of the daily requirement it makes a significant contribution when dietary vitamin intake is low an individual who depends on absorption of vitamins formed by bacteria in the large intestine may become vitamin deficient if treated with antibiotics that inhibit the vitamin producing species of bacteria as well as the intended disease causing bacteria 46 other bacterial products include gas flatus which is a mixture of nitrogen and carbon dioxide with small amounts of the gases hydrogen methane and hydrogen sulfide bacterial fermentation of undigested polysaccharides produces these some of the fecal odor is due to indoles metabolized from the amino acid tryptophan the normal flora is also essential in the development of certain tissues including the cecum and lymphatics citation needed they are also involved in the production of cross reactive antibodies these are antibodies produced by the immune system against the normal flora that are also effective against related pathogens thereby preventing infection or invasion the two most prevalent phyla of the colon are bacillota and bacteroidota the ratio between the two seems to vary widely as reported by the human microbiome project 47 bacteroides are implicated in the initiation of colitis and colon cancer bifidobacteria are also abundant and are often described as friendly bacteria 48 49 a mucus layer protects the large intestine from attacks from colonic commensal bacteria 50 clinical significance edit disease edit main article gastrointestinal disease following are the most common diseases or disorders of the colon angiodysplasia of the colon appendicitis chronic functional abdominal pain colitis colorectal cancer colorectal polyp constipation crohn s disease diarrhea diverticulitis diverticulosis hirschsprung s disease aganglionosis ileus intussusception irritable bowel syndrome pseudomembranous colitis ulcerative colitis and toxic megacolon colonoscopy edit main article colonoscopy colonoscopy image splenic flexure normal mucosa the spleen can be seen through it colonoscopy is the endoscopic examination of the large intestine and the distal part of the small bowel with a ccd camera or a fiber optic camera on a flexible tube passed through the anus it can provide a visual diagnosis e g ulceration polyps and grants the opportunity for biopsy or removal of suspected colorectal cancer lesions colonoscopy can remove polyps as small as one millimetre or less once polyps are removed they can be studied with the aid of a microscope to determine if they are precancerous or not it takes 15 years or fewer for a polyp to turn cancerous colonoscopy is similar to sigmoidoscopy the difference being related to which parts of the colon each can examine a colonoscopy allows an examination of the entire colon 1200 1500 mm in length a sigmoidoscopy allows an examination of the distal portion about 600 mm of the colon which may be sufficient because benefits to cancer survival of colonoscopy have been limited to the detection of lesions in the distal portion of the colon 51 52 53 a sigmoidoscopy is often used as a screening procedure for a full colonoscopy often done in conjunction with a stool based test such as a fecal occult blood test fobt fecal immunochemical test fit or multi target stool dna test cologuard or blood based test sept9 dna methylation test epi procolon 54 about 5 of these screened patients are referred to colonoscopy 55 virtual colonoscopy which uses 2d and 3d imagery reconstructed from computed tomography ct scans or from nuclear magnetic resonance mr scans is also possible as a totally non invasive medical test although it is not standard and still under investigation regarding its diagnostic abilities furthermore virtual colonoscopy does not allow for therapeutic maneuvers such as polyp tumour removal or biopsy nor visualization of lesions smaller than 5 millimeters if a growth or polyp is detected using ct colonography a standard colonoscopy would still need to be performed additionally surgeons have lately been using the term pouchoscopy to refer to a colonoscopy of the ileo anal pouch other animals edit the large intestine is truly distinct only in tetrapods in which it is almost always separated from the small intestine by an ileocecal valve in most vertebrates however it is a relatively short structure running directly to the anus although noticeably wider than the small intestine although the cecum is present in most amniotes only in mammals does the remainder of the large intestine develop into a true colon 56 in some small mammals the colon is straight as it is in other tetrapods but in the majority of mammalian species it is divided into ascending and descending portions a distinct transverse colon is typically present only in primates however the taeniae coli and accompanying haustra are not found in either carnivorans or ruminants the rectum of mammals other than monotremes is derived from the cloaca of other vertebrates and is therefore not truly homologous with the rectum found in these species 56 in some fish there is no true large intestine but simply a short rectum connecting the end of the digestive part of the gut to the cloaca in sharks this includes a rectal gland that secretes salt to help the animal maintain osmotic balance with the seawater the gland somewhat resembles a caecum in structure but is not a homologous structure 56 additional images edit intestines colon deep dissection anterior view see also edit this article uses anatomical terminology colectomy colonic ulcer large intestine chinese medicine references edit this article incorporates text in the public domain from page 1177 of the 20th edition of gray s anatomy 1918 1 2 3 small large intestine seer training training seer cancer gov retrieved 9 april 2025 large intestine retrieved 2016 07 24 cite web cs1 maint deprecated archival service link drake r l vogl w mitchell a w m 2010 gray s anatomy for students phil...
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