The colon , also known as colon or colon, is the last part of the digestive tract and digestive system in vertebrates. Water is absorbed here and residual waste material is stored as feces before disposal by bowel movements.
Most sources define the large intestine as a combination of cecum, colon , rectum, and anal hole. Some other sources exclude the anal canal.
In humans, the large intestine begins in the pelvic right iliac region, right at or below the waist, where it joins to the end of the small intestine in the cecum, via the ileocecal valve. Then continue as the colon rises to the abdomen, along the abdominal cavity as a transverse colon, and then down to the rectum and the end point in the anal canal. Overall, in humans, the large intestine is about 1.5 meters (5 feet) long, which is about one fifth of the entire length of the gastrointestinal tract.
Video Large intestine
Structure
The large intestine is the last part of the digestive system. It extracts water and salt from solid waste before they are eliminated from the body and is the place where the fermented aided flora (mostly bacteria) of unabsorbed material occurs. In contrast to the small intestine, the colon does not play a major role in the absorption of food and nutrients. About 1.5 liters or 45 ounces of water arrive in the colon every day.
The length of a human male colon is 166 cm (range 80 to 313 cm), on average, for women 155 cm (range 80 to 214 cm).
Section
In mammals, the colon consists of five parts: cecum plus ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.
The part of the colon is:
- Upgraded colons include caecum and appendix
- The transverse colon includes a colicky arch and transversal mesocolon
- Descendent colon
- Sigmoid colon - s shaped area of ​​the colon
- Rectum
The parts of the colon are either intraperitoneal or behind it in the retroperitoneum. Retroperitoneal organs generally do not have complete peritoneal coverings, so they stay on site. The intrapitoneal organs are completely surrounded by the peritoneum and therefore move. Of the colon, ascending colon, descending colon and retroperitoneal rectum, while cecum, appendix, transverse colon and sigmoid colon are intraperitoneal. This is important because it affects which organs can be easily accessed during surgery, such as laparotomy.
The mean inner diameter of the colon in centimeters (with the spans in parentheses) is cecum 8.7 (8.0-10.5), ascending colon 6.6 (6.0-7.0), transverse colon 5.8 (5.0-6.5), descending colon/sigmoid 6.3 (6.0 -6.8) and rectum near the rectal/sigmoid junction 5.7 (4.5-7.5).
Sekum and appendix
The caecum is the first part of the colon and involved in digestion, whereas the embryological developing appendix of it, is a colonic structure, is not involved in digestion and is considered part of lymphoid tissue associated with the intestine. The appendix function is uncertain, but some sources believe that the appendix has a role in sample housing of intestinal microflora, and is able to help refill the colon with bacteria if the microflora has been damaged during immune travel. reaction. The appendix has also been shown to have high concentrations of lymphatic cells.
The ascending colon
Ascending colon is the first of four parts of the colon. It is connected to the small intestine by the part of the intestine called the cecum. The ascending colon goes upward through the abdominal cavity toward the transverse colon about eight inches (20 cm).
One of the major functions of the colon is to remove water and other essential nutrients from waste materials and recycle them. When the waste material comes out of the small intestine through the ileocecal valve, it will move to the cecum and then to the ascending colon where this extraction process begins. Unwanted waste material is moved upwards towards the transverse colon by peristaltic action. The ascending colon is sometimes attached to the appendix via the Gerlach valve. In ruminants, ascending colon is known as colon . Considering all age and sex, colon cancer occurs here most often (41%).
Transverse colon
The transverse colon is part of the colon of the mucus of the liver, also known as the right colic, (the turn of the large intestine by the liver) to the celiac flexure also known as the left colic, (the turn of the large intestine by the spleen). The transverse colon suspends in the abdomen, attached to it with a large fold of peritoneum called the larger omentum. On the posterior side, the transverse colon is connected to the posterior abdominal wall by a mesenterium known as transverse mesocolon.
The transverse colon is wrapped in the peritoneum, and therefore moves (unlike the parts of the colon immediately before and after).
Proximal two-thirds of the transverse colon is diffused by the middle colic artery, the branch of the superior mesenteric artery (SMA), while the last third is supplied by the inferior mesenteric branches of the IMA. The "watershed" area between these two blood supplies, which represents the embryological division between midgut and hindgut, is an ischemic sensitive area.
Colon decreased
The descending colon is part of the large intestine of the splenic ligament to the early sigmoid colon. One of the functions of the descending colon in the digestive system is to store the impurities to be emptied into the rectum. It's retroperitoneal in two-thirds of humans. On the other three, it has mesentery (usually short). The arterial supply comes from the left colic artery. The descending colon is also called distal intestine , as it is further along the digestive tract than the proximal bowel. Intestinal flora is very dense in this region.
Sigmoid colon
The sigmoid colon is part of the colon after the descending colon and before the rectum. The name sigmoid means S-shaped (see sigmoid; cf. sigmoid sinus). The walls of the sigmoid colon are muscular, and contract to increase the pressure inside the colon, causing the stool to move into the rectum.
The sigmoid colon is administered with blood from several branches (usually between 2 and 6) of the sigmoid artery, the branch of the IMA. IMA ends up as superior rectal artery.
Sigmoidoscopy is a common diagnostic technique used to examine sigmoid colonies.
Rectum
The rectum is the last part of the colon. It holds dirt that forms waiting for removal through the bowel movement.
Appearance
The cum - the first part of the colon
- Taeniae coli - three bands of smooth muscle
- Haustra - a bulge caused by taeniae coli contraction
- Epiploic appendages - small fat accumulations on viscera
Taenia coli runs the length of the colon. Because taenia coli is shorter than the large intestine itself, the colon becomes sacculated , forming a haustra of the large intestine which is an intraluminal projection like a shelf.
Blood supply
The supply of arteries to the colon is derived from the branches of the superior mesenteric artery (SMA) and the inferior mesenteric artery (IMA). The flow between these two systems communicates via a "marginal artery" that runs parallel to the colon for its entire length. Historically, it has been believed that the Riolan arc, or mesenteric mesenteric dutch (from Moskowitz), is a variable vessel that connects the proximal SMA to the proximal IMA which can be very important if one of the vessels is clogged. However, recent research conducted with improved imaging technology has questioned the true existence of these vessels, with some experts calling for the removal of terms from the medical literature in the future.
Venous drainage usually reflects the supply of colonic arteries, with the inferior mesenteric veins flowing into the venous spleen, and the superior mesenteric veins joining the veins of the limbs form the hepatic portal vein which then enters the liver.
Lymphatic drainage
Lymphatic drainage from the ascending and proximal colon of two thirds of the transverse colon is to the colic and the mesenteric lymph nodes, which flow into the cisterna chyli. Lymph from the distal third of the transverse colon, descending colon, sigmoid colon, and upper rectum enter the mesenteric and colic inferior lymph nodes. The lower rectum to the anal canal above the pectinic conduit flows into the internal iliac node. The anal canal below the pectinate line flows into the superficial inguinal nodes. The pectinate line only roughly marks this transition.
Supply of nerves
Development
Variations
A variation in the normal anatomy of the colon occurs when an additional loop is formed, producing a large bowel longer up to five meters from the usual. This condition, referred to as excessive intestine, usually has no major direct health consequences, although rarely volvulus, results in obstruction and requires immediate medical attention. A significant indirect health consequence is that the use of standard adult colonoscopy is difficult and in some cases impossible when redundant colon is present, although special variants on the instrument (including pediatric variants) are useful in addressing this problem.
Maps Large intestine
Microanatomy
Colonic liquid
The walls of the colon are coated with a simple columnar epithelium with invagination. Invagination is called the gut or colon crypts.
Colon bowl shaped like a microscopic thick-walled test tube with a central hole along the tube (lumen crypt). Four parts of the network are shown here, two cutting the long axis of the crypts and two pieces parallel to the long axis. In these images cells have been colored by immunohistochemistry to show brown-orange color if the cell produces a mitochondrial protein called cytochrome c oxidase subunit I (CCOI). The cell nucleus (located on the outer edge of the cell lining the basement wall) is grayish blue with hematoxylin. As seen in panels C and D, the crypts are about 75 to about 110 cells. Baker et al. found that the average crypt circumference was 23 cells. Thus, with the images shown here, there is an average of about 1,725 ​​to 2,530 cells per crypt of the colon. Nooteboom et al. measuring the number of cells in a small number of crypts reporting a range of 1500 to 4900 cells per crypt of the colon. Cells are produced in the crypt base and migrate upward along the crypt shaft before being dumped into the colonic lumen days later. There are 5 to 6 stem cells in the basement basement.
As predicted from the image in panel A, there are about 100 crypt colon per square millimeter of the colonic epithelium. Since the average length of the human colon is 160.5 cm and the mean circumference in the colon is 6.2 cm, the surface epithelial region in the human intestine has an average area of ​​approximately 995 cm, which covers 9.950 million (near 10 million ) crypts.
In the four tissue sections shown here, many of the intestinal glands have cells with mitochondrial DNA mutations in the CCOI gene and appear mostly white, with their primary color being the blue-gray coloring of the nuclei. As seen in panel B, some of the stem cells of the three crypts appear to have mutations in CCOI , so that 40% to 50% of the cells arising from the stem cells form a white segment in the cross-cut area.
Overall, the percentage deficiency of crypts for CCOI is less than 1% before age 40, but then increases linearly with age. Cryptic crypts are deficient for CCOI in women reaching an average of 18% in women and 23% in men at the age of 80-84 years.
Crypts from the colon can reproduce by fission, as seen in panel C, where a crypt fission to form two crypts, and in panel B where at least one crypt seems to be fissionable. Most deficient crypts in CCOI are in clusters of crypts with two or more cryptic crypt-deficits adjacent to each other (see panel D).
Mucosa
About 150 of the thousands of protein-encoding genes are expressed in the large intestine, some specific for mucous membranes in different regions and include CEACAM7.
Function
The large intestine absorbs water and residual nutrients that can be absorbed from food before sending an indigestible material into the rectum. The large intestine absorbs vitamins created by colonic bacteria, such as vitamin K (especially important because daily consumption of vitamin K is usually not enough to maintain adequate blood coagulation), thiamine and riboflavin. It also condenses the stool, and keeps the dirt in the rectum until it is removed through the anus in defecation. The large intestine also secretes K and Cl-. Chloride secretion increases in cystic fibrosis. Recycling of various nutrients occurs in the colon. Examples include carbohydrate fermentation, short chain fatty acids, and cycling urea.
The appendix attaches to the inferior surface of the cecum, and contains a small amount of mucosal-linked lymphoid tissue that provides an undetermined role appendix to immunity. However, the appendix is ​​known to be important in fetal life because it contains endocrine cells that release biogenic amines and peptide hormones that are essential for homeostasis during early growth and development. Appendix may be removed without obvious damage or consequences to the patient.
By the time the chyme has reached this tube, most of the nutrients and 90% of the water has been absorbed by the body. At this point some electrolytes such as sodium, magnesium, and chloride are left behind and the undigested portions of the digested food (for example, most of the amylose is ingested, starch that has been protected from digestion until now, and dietary fiber, most of which are carbohydrates can not be digested either in soluble or insoluble form). When the chyme travels through the large intestine, most of the remaining water is removed, while the chyme is mixed with mucus and bacteria (known as intestinal flora), and becomes a feces. Ascending colon receives feces as a liquid. The muscles of the large intestine then move the aqueous waste material forward and slowly absorb all the excess water, causing the stool to solidify gradually as they move into the descending colon.
Bacteria break down some fibers for their own food and create acetate, propionate, and butyrate as waste products, which in turn are used by layers of colon cells for food. No protein available. In humans, perhaps 10% of undigested carbohydrates thus become available, although this may vary with diet; in other animals, including apes and other primates, which have larger proportional colonies, are more available, thus allowing a higher share of plant material in food. The large intestine does not produce digestive enzymes - chemical digestion is complete in the small intestine before the chyme reaches the large intestine. The pH in the colon varies between 5.5 and 7 (slightly acid to neutral).
Standing gradient osmosis
The absorption of water in the colon usually progresses against the transmucosal osmotic pressure gradient. The standing gradient osmosis is the water reabsorption of the osmotic gradient in the gut. The cells that occupy the lining of the intestine pump sodium ions into the intercellular space, increasing the osmolarity of the intercellular fluid. This hypertonic fluid creates an osmotic pressure that moves water into the lateral intercellular space through osmosis through tight intersections and adjacent cells, which then move across the basement membrane and into the capillaries, while more sodium ions are pumped again into the intercellular fluid. Although water moves down the osmotic gradient at each individual step, overall, water usually moves against the osmotic gradient as it pumps sodium ions into the liquid between cells. This allows the colon to absorb water even though the blood in the capillaries becomes hypotonic compared to the fluid inside the intestinal lumen.
Flora colon
Large intestine houses more than 700 species of bacteria that perform various functions, as well as fungi, protozoa, and archaea. The diversity of species varies by geography and diet. Microbes in the human distal intestine often amount to about 100 trillion, and can weigh about 200 grams (0.44 Ib). These masses of most symbiotic microbes have recently been called the latest human organs to "be discovered" or in other words, "forgotten organs".
The large intestine absorbs some products formed by bacteria that inhabit this region. Undigested polysaccharides (fibers) are metabolized into short chain fatty acids by bacteria in the colon and absorbed by passive diffusion. Bicarbonate secreted by the colon helps to neutralize the increased acidity resulting from the formation of these fatty acids.
These bacteria also produce large amounts of vitamins, especially vitamin K and biotin (vitamin B), for absorption into the blood. Although the source of this vitamin, in general, provides only a small portion of the daily requirement, it makes a significant contribution when dietary vitamin intake is low. A person who relies on the absorption of vitamins formed by bacteria in the colon can become vitamin deficient when treated with antibiotics that inhibit the vitamin-producing species of bacteria and disease-causing bacteria.
Other bacterial products include gas (flatus), which is a mixture of nitrogen and carbon dioxide, with a small amount of hydrogen gas, methane, and hydrogen sulfide. Bacterial fermentation of undigested polysaccharides produces this. Some fecal odors are caused by indoles, which are metabolized from tryptophan amino acids. Normal flora is also important in the development of certain tissues, including cecum and lymphatics.
They are also involved in the production of cross-reactive antibodies. These are antibodies produced by the immune system against normal flora, which are also effective against the associated pathogens, thereby preventing infection or invasion.
The two most common phyla of the colon are firmicutes and bacteroides. The ratios between the two seem to vary greatly as reported by the Human Microbiome Project. Bacteriaids are involved in the initiation of colitis and colon cancer. Bifidobacteria are also abundant, and are often described as 'friendly bacteria'.
The mucus layer protects the colon from the invasion of the commensal colonic bacteria.
Clinical interests
Disease
The following are the most common diseases or intestinal disorders:
colonoscopy
Colonoscopy is the examination of the colon endoscopy and the distal portion of the small intestine with a CCD camera or a fiber-optic camera on a flexible tube passing through the anus. This can provide a visual diagnosis (eg ulceration, polyps) and provide opportunities for biopsy or removal of suspected colorectal cancer lesions. Colonoscopy can remove polyps as small as a millimeter or less. Once the polyps are removed, they can be studied with the help of a microscope to determine if they are precancerous or not. It takes 15 years or less for polyps to turn into cancer.
Colonoscopy is similar to sigmoidoscopy - a difference related to which part of the colon can be examined. Colonoscopy allows examination of entire colon (length 1200-1500 mm). Sigmoidoscopy allows examination of the distal (about 600 mm) portion of the colon, which may be sufficient as the benefits for survival of colonoscopy cancer have been limited to detection of lesions in the distal portion of the colon.
Sigmoidoscopy is often used as a screening procedure for full colonoscopy, often performed simultaneously with fecal occult blood test (FOEC). About 5% of these screened patients are referred to colonoscopy.
A virtual colonoscopy, which uses 2D and 3D images reconstructed from computed tomography (CT) scans or from nuclear magnetic resonance scanning (MR), is also possible, as a completely non-invasive medical test, though not standardized and still under investigation with regard to its diagnostic ability. Furthermore, virtual colonoscopy does not allow for therapeutic maneuvers such as removal of polyps/tumors or biopsy or visualization of lesions smaller than 5 millimeters. If growth or polyps are detected using CT colonography, standard colonoscopy still needs to be done. In addition, surgeons have recently used the term pouchoscopy to refer to colonoscopy in ileo-anal pouches.
Other animals
The colon is completely different only in tetrapods, where it is almost always separated from the small intestine by the ileocaecal valve. In most vertebrates, however, this is a relatively short structure that runs directly into the anus, although it feels wider than the small intestine. Although cecum is present in most amniotes, only in mammals that do the rest of the large intestine develop into the correct intestine.
In some small mammals, the large intestine is straight, as in other tetrapods, but, in most mammalian species, it is divided into increasing and descending parts; Different transverse colon is usually present only in primates. However, taeniae coli and haustral companions are not found in either carnivores or ruminants. The mammalian (other than monotremata) rectum comes from other vertebrate cloaca, and therefore, is not really homologous to the "rectum" found in this species.
In fish, there is no correct large intestine, but only a short rectum connecting the end of the digestive portion of the intestine to the cloaca. In sharks, these include the rectum glands that secrete salt to help the animals maintain an osmotic balance with sea water. The glands resemble the cecum in the structure, but not the homologous structure.
Additional images
See also
- Colon (Chinese medicine)
References
This article combines text in the public domain of page 1177 of the 20th edition of Gray's Anatomy (1918)
External links
- 09-118h. in Merck Manual Diagnosis and Home Edition Therapy
Source of the article : Wikipedia
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