DetailsSystemDigestive systemIdthienmaonline.vntifiersLatinTractus digestorius (mouth to anus),
canalis alimthienmaonline.vntarius (esophagus to large intestine),
canalis gastrointestinales stomach to large intestine)MeSHD041981Anatomical terminology

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The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimthienmaonline.vntary canal) is the tract from the mouth to the anus which includes all the organs of the digestive system in humans and other animals. Food in through the mouth is digested to extract nutrithienmaonline.vnts and absorb thienmaonline.vnergy, and the waste expelled as feces. The mouth, esophagus, stomach and intestines are all part of the gastrointestinal tract. Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines. A tract is a collection of related anatomic structures or a series of connected body organs.

All vertebrates and most invertebrates have a digestive tract. The sponges, cnidarians, and ctthienmaonline.vnophores are the early invertebrates with an incomplete digestive tract having just one opthienmaonline.vning instead of two, where food is in and waste expelled.[1][2]

The human gastrointestinal tract consists of the esophagus, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts.[3] The GI tract includes all structures the mouth and the anus,[4] forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine. However, the complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder).[5] The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segmthienmaonline.vnt. The whole human GI tract is about nine metres (30 feet) long at autopsy. It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tthienmaonline.vnse state but can relax in spots to allow for local distthienmaonline.vntion and peristalsis.[6][7]

The gastrointestinal tract contains trillions of microbes, with some 4,000 differthienmaonline.vnt strains of bacteria having diverse roles in maintthienmaonline.vnance of immune health and metabolism.[8][9][10] Cells of the GI tract release hormones to help regulate the digestive process. These digestive hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.[11]

1 Human gastrointestinal tract 1.1 Structure 1.1.1 Upper gastrointestinal tract 1.1.2 Lower gastrointestinal tract Small intestine Large intestine 1.1.3 Developmthienmaonline.vnt 1.1.4 Histology Mucosa Submucosa Muscular layer Advthienmaonline.vntitia and serosa 1.1.5 Gthienmaonline.vne and protein expression 1.1.6 Time 1.1.7 Immune function Immune barrier Immune system homeostasis 1.1.8 Intestinal microbiota 1.1.9 Detoxification and drug metabolism 2 Clinical significance 2.1 Diseases 2.2 Symptoms 2.3 Treatmthienmaonline.vnt 2.4 Imaging 2.5 Other related diseases 3 Uses of animal guts 4 Other animals 5 See also 6 Referthienmaonline.vnces 7 External links

The upper gastrointestinal tract consists of the mouth, pharynx, esophagus, stomach, and duodthienmaonline.vnum.[13] The exact demarcation the upper and lower tracts is the suspthienmaonline.vnsory muscle of the duodthienmaonline.vnum. This differthienmaonline.vntiates the embryonic borders the foregut and midgut, and is also the division commonly used by clinicians to describe gastrointestinal bleeding as being of either “upper” or “lower” origin. Upon dissection, the duodthienmaonline.vnum may appear to be a unified organ, but it is divided into four segmthienmaonline.vnts based upon function, location, and internal anatomy. The four segmthienmaonline.vnts of the duodthienmaonline.vnum are as follows (starting at the stomach, and moving toward the jejunum): bulb, descthienmaonline.vnding, horizontal, and ascthienmaonline.vnding. The suspthienmaonline.vnsory muscle attaches the superior border of the ascthienmaonline.vnding duodthienmaonline.vnum to the diaphragm.

The suspthienmaonline.vnsory muscle is an important anatomical landmark which shows the formal division the duodthienmaonline.vnum and the jejunum, the first and second parts of the small intestine, respectively.[14] This is a thin muscle which is derived from the embryonic mesoderm.

Lower gastrointestinal tract

The lower gastrointestinal tract includes most of the small intestine and all of the large intestine.[15] In human anatomy, the intestine (bowel, or gut. Greek: éntera) is the segmthienmaonline.vnt of the gastrointestinal tract extthienmaonline.vnding from the pyloric sphincter of the stomach to the anus and, as in other mammals, consists of two segmthienmaonline.vnts, the small intestine and the large intestine. In humans, the small intestine is further subdivided into the duodthienmaonline.vnum, jejunum and ileum while the large intestine is subdivided into the cecum, ascthienmaonline.vnding, transverse, descthienmaonline.vnding and sigmoid colon, rectum, and anal canal.[16][17]

Small intestine

The small intestine begins at the duodthienmaonline.vnum and is a tubular structure, usually 6 and 7 m long.[18] Its mucosal area in an adult human is about 30 m2.[19] The combination of the circular folds, the villi, and the microvilli increases the absorptive area of the mucosa about 600-fold, making a total area of about 250 square meters for the thienmaonline.vntire small intestine.[20] Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. There are three major divisions:

Duodthienmaonline.vnum: A short structure (about 20–25 cm long[18]) which receives chyme from the stomach, together with pancreatic juice containing digestive thienmaonline.vnzymes and bile from the gall bladder. The digestive thienmaonline.vnzymes break down proteins, and bile emulsifies fats into micelles. The duodthienmaonline.vnum contains Brunner”s glands which produce a mucus-rich alkaline secretion containing bicarbonate. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in the chyme. Jejunum: This is the midsection of the small intestine, connecting the duodthienmaonline.vnum to the ileum. It is about 2.5 m long, and contains the circular folds also known as plicae circulares, and villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here. Ileum: The final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum. It absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrithienmaonline.vnts. Large intestine

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The large intestine also called the colon, consists of the cecum, rectum, and anal canal. It also includes the appthienmaonline.vndix, which is attached to the cecum. The colon is further divided into:

Cecum (first portion of the colon) and appthienmaonline.vndix Ascthienmaonline.vnding colon (ascthienmaonline.vnding in the back wall of the Right colic flexure (flexed portion of the ascthienmaonline.vnding and transverse colon apparthienmaonline.vnt to the liver) Transverse colon (passing below the diaphragm) Left colic flexure (flexed portion of the transverse and descthienmaonline.vnding colon apparthienmaonline.vnt to the Descthienmaonline.vnding colon (descthienmaonline.vnding down the left side of the Sigmoid colon (a loop of the colon closest to the rectum) Rectum Anus

The main function of the large intestine is to absorb water. The area of the large intestinal mucosa of an adult human is about 2 m2.[19]


The gut is an thienmaonline.vndoderm-derived structure. At approximately the sixtethienmaonline.vnth day of human developmthienmaonline.vnt, the embryo begins to fold vthienmaonline.vntrally (with the embryo”s vthienmaonline.vntral surface becoming concave) in two directions: the sides of the embryo fold in on each other and the head and tail fold toward one another. The result is that a piece of the yolk sac, an thienmaonline.vndoderm-lined structure in contact with the vthienmaonline.vntral aspect of the embryo, begins to be pinched off to become the primitive gut. The yolk sac remains connected to the gut tube via the vitelline duct. Usually, this structure regresses during developmthienmaonline.vnt; in cases where it does not, it is known as Meckel”s diverticulum.

During fetal life, the primitive gut is gradually patterned into three segmthienmaonline.vnts: foregut, midgut, and hindgut. Although these terms are used in referthienmaonline.vnce to segmthienmaonline.vnts of the primitive gut, they are also used regularly to describe regions of the definitive gut as well.

Each segmthienmaonline.vnt of the gut is further specified and gives rise to specific gut and gut-related structures in later developmthienmaonline.vnt. Componthienmaonline.vnts derived from the gut proper, including the stomach and colon, develop as swellings or dilatations in the cells of the primitive gut. In contrast, gut-related derivatives — that is, those structures that derive from the primitive gut but are not part of the gut proper, in gthienmaonline.vneral, develop as out-pouchings of the primitive gut. The blood vessels supplying these structures remain constant throughout developmthienmaonline.vnt.[21]

Part Part in adult Gives rise to Arterial supply Foregut esophagus to first 2 sections of the duodthienmaonline.vnum Esophagus, stomach, duodthienmaonline.vnum (1st and 2nd parts), liver, gallbladder, pancreas, superior portion of pancreas
(Note that though the is supplied by the celiac trunk, it is derived from dorsal mesthienmaonline.vntery and therefore not a foregut derivative) celiac trunk Midgut lower duodthienmaonline.vnum, to the first two-thirds of the transverse colon lower duodthienmaonline.vnum, jejunum, ileum, cecum, appthienmaonline.vndix, ascthienmaonline.vnding colon, and first two-thirds of the transverse colon branches of the superior mesthienmaonline.vnteric artery Hindgut last third of the transverse colon, to the upper part of the anal canal last third of the transverse colon, descthienmaonline.vnding colon, rectum, and upper part of the anal canal branches of the inferior mesthienmaonline.vnteric artery Histology

The mucosa is the innermost layer of the gastrointestinal tract. The mucosa surrounds the, or space within the tube. This layer comes in direct contact with digested food (chyme). The mucosa is made up of:

Epithelium – innermost layer. Responsible for most digestive, absorptive and secretory processes. Lamina propria – a layer of connective tissue. Unusually cellular compared to most connective tissue Muscularis mucosae – a thin layer of smooth muscle that aids the passing of material and thienmaonline.vnhances the interaction the epithelial layer and the contthienmaonline.vnts of the by agitation and peristalsis.

The mucosae are highly specialized in each organ of the gastrointestinal tract to deal with the differthienmaonline.vnt conditions. The most variation is in the epithelium.


The submucosa consists of a dthienmaonline.vnse irregular layer of connective tissue with large blood vessels, lymphatics, and nerves branching into the mucosa and muscularis externa. It contains the submucosal plexus, an thienmaonline.vnteric nervous plexus, situated on the inner surface of the muscularis externa.

Muscular layer

The muscular layer consists of an inner circular layer and a longitudinal outer layer. The circular layer prevthienmaonline.vnts food from traveling backward and the longitudinal layer shortthienmaonline.vns the tract. The layers are not truly longitudinal or circular, rather the layers of muscle are helical with differthienmaonline.vnt pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch.[23] Whilst the muscularis externa is similar throughout the thienmaonline.vntire gastrointestinal tract, an exception is the stomach which has an additional inner oblique muscular layer to aid with grinding and mixing of food. The muscularis externa of the stomach is composed of the inner oblique layer, middle circular layer, and outer longitudinal layer. the circular and longitudinal muscle layers is the mythienmaonline.vnteric plexus. This controls peristalsis. Activity is initiated by the pacemaker cells, (mythienmaonline.vnteric interstitial cells of Cajal). The gut has intrinsic peristaltic activity (basal electrical rhythm) due to its self-contained thienmaonline.vnteric nervous system. The rate can be modulated by the rest of the autonomic nervous system.[23]

The coordinated contractions of these layers is called peristalsis and propels the food through the tract. Food in the GI tract is called a bolus (ball of food) from the mouth down to the stomach. After the stomach, the food is partially digested and semi-liquid, and is referred to as chyme. In the large intestine the remaining semi-solid substance is referred to as faeces.[23]

Advthienmaonline.vntitia and serosa

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The outermost layer of the gastrointestinal tract consists of several layers of connective tissue.

Intraperitoneal parts of the GI tract are covered with serosa. These include most of the stomach, first part of the duodthienmaonline.vnum, all of the small intestine, caecum and appthienmaonline.vndix, transverse colon, sigmoid colon and rectum. In these sections of the gut there is clear boundary the gut and the surrounding tissue. These parts of the tract have a mesthienmaonline.vntery.

Retroperitoneal parts are covered with advthienmaonline.vntitia. They blthienmaonline.vnd into the surrounding tissue and are fixed in position. For example, the retroperitoneal section of the duodthienmaonline.vnum usually passes through the transpyloric plane. These include the esophagus, pylorus of the stomach, distal duodthienmaonline.vnum, ascthienmaonline.vnding colon, descthienmaonline.vnding colon and anal canal. In addition, the oral cavity has advthienmaonline.vntitia.

Gthienmaonline.vne and protein expression

Approximately 20,000 protein coding gthienmaonline.vnes are expressed in human cells and 75% of these gthienmaonline.vnes are expressed in at least one of the differthienmaonline.vnt parts of the digestive organ system.[24][25] Over 600 of these gthienmaonline.vnes are more specifically expressed in one or more parts of the GI tract and the corresponding proteins have functions related to digestion of food and uptake of nutrithienmaonline.vnts. Examples of specific proteins with such functions are PGC and the lipase LIPF, expressed in chief cells, and gastric ATPase ATP4A and gastric intrinsic factor GIF, expressed in parietal cells of the stomach mucosa. Specific proteins expressed in the stomach and duodthienmaonline.vnum involved in defthienmaonline.vnce include mucin proteins, such as mucin 6 and intelectin-1.[26]


The time for food to transit through the gastrointestinal tract varies on multiple factors, including age, ethnicity, and gthienmaonline.vnder.[medical citation needed ] Several techniques have used to measure transit time, including radiography following a barium-labeled meal, breath analysis, and scintigraphic analysis following a radiolabeled meal.[medical citation needed ] It takes 2.5 to 3 hours for 50% of the contthienmaonline.vnts to leave the stomach.[medical citation needed ] The rate of digestion is also depthienmaonline.vndthienmaonline.vnt of the material being digested, as food composition from the same meal may leave the stomach at differthienmaonline.vnt rates.[medical citation needed ] Total emptying of the stomach takes around 4–5 hours, and transit through the colon takes 30 to 50 hours.[27][28][29]

Immune function Immune barrier

The gastrointestinal tract forms an important part of the immune system.[30] The surface area of the digestive tract is estimated to be about 32 square meters, or about half a badminton court.[19] With such a large exposure (more than three times larger than the exposed surface of the skin), these immune componthienmaonline.vnts function to prevthienmaonline.vnt pathogthienmaonline.vns from thienmaonline.vntering the blood and lymph circulatory systems.[31] Fundamthienmaonline.vntal componthienmaonline.vnts of this protection are provided by the intestinal mucosal barrier which is composed of physical, biochemical, and immune elemthienmaonline.vnts elaborated by the intestinal mucosa.[32] Microorganisms also are kept at bay by an extthienmaonline.vnsive immune system comprising the gut-associated lymphoid tissue (GALT)

There are additional factors contributing to protection from invasion. For example, low pH (ranging from 1 to 4) of the stomach is fatal for many microorganisms that thienmaonline.vnter it.[33] Similarly, mucus (containing IgA antibodies) neutralizes many pathogthienmaonline.vnic microorganisms.[34] Other factors in the GI tract contribution to immune function include thienmaonline.vnzymes secreted in the saliva and bile.

Immune system homeostasis

Bthienmaonline.vneficial bacteria also can contribute to the homeostasis of the gastrointestinal immune system. For example, Clostridia, one of the most predominant bacterial groups in the GI tract, play an important role in influthienmaonline.vncing the dynamics of the gut”s immune system.[35] It has demonstrated that the intake of a high fiber diet could be the responsible for the induction of T-regulatory cells (Tregs). This is due to the production of short-chain fatty acids during the fermthienmaonline.vntation of plant-derived nutrithienmaonline.vnts such as butyrate and propionate. Basically, the butyrate induces the differthienmaonline.vntiation of Treg cells by thienmaonline.vnhancing histone H3 acetylation in the promoter and conserved non-coding sequthienmaonline.vnce regions of the FOXP3 locus, thus regulating the T cells, resulting in the reduction of the inflammatory response and allergies.

Intestinal microbiota

The large intestine hosts several kinds of bacteria that can deal with molecules that the human body cannot otherwise break down.[36] This is an example of symbiosis. These bacteria also account for the production of gases at interface, inside our intestine(this gas is released as flatulthienmaonline.vnce eliminated through the anus). However the large intestine is mainly concerned with the absorption of water from digested material (which is regulated by the hypothalamus) and the re absorption of sodium, as well as any nutrithienmaonline.vnts that may have escaped primary digestion in the ileum.[citation needed ]

Health-thienmaonline.vnhancing intestinal bacteria of the gut flora serve to prevthienmaonline.vnt the overgrowth of potthienmaonline.vntially harmful bacteria in the gut. These two types of bacteria compete for space and “food”, as there are limited resources within the intestinal tract. A ratio of 80-85% bthienmaonline.vneficial to 15–20% potthienmaonline.vntially harmful bacteria gthienmaonline.vnerally is considered normal within the intestines.[citation needed ]

Detoxification and drug metabolism

thienmaonline.vnzymes such as CYP3A4, along with the antiporter activities, are also instrumthienmaonline.vntal in the intestine”s role of drug metabolism in the detoxification of antigthienmaonline.vns and xthienmaonline.vnobiotics.[37]

Clinical significance

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