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The **gastrointestinal tract**, (**GI tract**, **GIT**, **digestive tract**, **digestion tract**, **alimentary canal**) is the tract from the [mouth](https://en.wikipedia.org/wiki/Mouth) to the [anus](https://en.wikipedia.org/wiki/Anus) which includes all the [organs](https://en.wikipedia.org/wiki/Organ_(anatomy)) of the [digestive system](https://en.wikipedia.org/wiki/Digestive_system) in humans and other [animals](https://en.wikipedia.org/wiki/Animal). Food taken in through the mouth is [digested](https://en.wikipedia.org/wiki/Digestion) to extract nutrients and absorb energy, and the waste expelled as [feces](https://en.wikipedia.org/wiki/Feces). The [mouth](https://en.wikipedia.org/wiki/Mouth), [esophagus](https://en.wikipedia.org/wiki/Esophagus), [stomach](https://en.wikipedia.org/wiki/Stomach) and [intestines](https://en.wikipedia.org/wiki/Intestines) are all part of the gastrointestinal tract. *Gastrointestinal* is an adjective meaning of or pertaining to the [stomach](https://en.wikipedia.org/wiki/Stomach) and intestines. A tract is a collection of related anatomic structures or a series of connected body organs.

All [vertebrates](https://en.wikipedia.org/wiki/Vertebrate) and most [invertebrates](https://en.wikipedia.org/wiki/Invertebrate) have a digestive tract. The [sponges](https://en.wikipedia.org/wiki/Sponge), [cnidarians](https://en.wikipedia.org/wiki/Cnidarian), and [ctenophores](https://en.wikipedia.org/wiki/Ctenophores) are the early invertebrates with an incomplete digestive tract having just one opening instead of two, where food is taken in and waste expelled.[\[1\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-CK12-1)[\[2\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-RuppertBarnes2004BilateriaGut-2)

The human gastrointestinal tract consists of the [esophagus](https://en.wikipedia.org/wiki/Esophagus), [stomach](https://en.wikipedia.org/wiki/Stomach), and intestines, and is divided into the upper and lower gastrointestinal tracts.[\[3\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-3) The GI tract includes all structures between the [mouth](https://en.wikipedia.org/wiki/Human_mouth) and the [anus](https://en.wikipedia.org/wiki/Human_anus),[\[4\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-4) forming a continuous passageway that includes the main organs of digestion, namely, the [stomach](https://en.wikipedia.org/wiki/Stomach), [small intestine](https://en.wikipedia.org/wiki/Small_intestine), and [large intestine](https://en.wikipedia.org/wiki/Large_intestine). However, the complete [human digestive system](https://en.wikipedia.org/wiki/Human_digestive_system) is made up of the gastrointestinal tract plus the accessory organs of digestion (the [tongue](https://en.wikipedia.org/wiki/Tongue), [salivary glands](https://en.wikipedia.org/wiki/Salivary_gland), [pancreas](https://en.wikipedia.org/wiki/Pancreas), [liver](https://en.wikipedia.org/wiki/Liver) and [gallbladder](https://en.wikipedia.org/wiki/Gallbladder)).[\[5\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-5) The tract may also be divided into [foregut](https://en.wikipedia.org/wiki/Foregut), [midgut](https://en.wikipedia.org/wiki/Midgut), and [hindgut](https://en.wikipedia.org/wiki/Hindgut), reflecting the [embryological](https://en.wikipedia.org/wiki/Embryology) origin of each segment. The whole human GI tract is about nine metres (30 feet) long at [autopsy](https://en.wikipedia.org/wiki/Autopsy). It is considerably shorter in the living body because the intestines, which are tubes of [smooth muscle tissue](https://en.wikipedia.org/wiki/Smooth_muscle_tissue), maintain constant [muscle tone](https://en.wikipedia.org/wiki/Muscle_tone) in a halfway-tense state but can relax in spots to allow for local distention and [peristalsis](https://en.wikipedia.org/wiki/Peristalsis).[\[6\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-G._C._J._P._pp._290%E2%80%93294-6)[\[7\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-Raines_Arbour_Thompson_Figueroa-Bodine_pp._67%E2%80%9372-7)

The gastrointestinal tract contains trillions of [microbes](https://en.wikipedia.org/wiki/Microbe), with some 4,000 different [strains](https://en.wikipedia.org/wiki/Strain_(biology)) of [bacteria](https://en.wikipedia.org/wiki/Bacteria) having diverse roles in maintenance of [immune health](https://en.wikipedia.org/wiki/Immune_system) and [metabolism](https://en.wikipedia.org/wiki/Gut_flora#Metabolism).[\[8\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-8)[\[9\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-9)[\[10\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-Clarke2014rev-10) Cells of the GI tract release [hormones](https://en.wikipedia.org/wiki/Hormone) to help regulate the digestive process. These [digestive hormones](https://en.wikipedia.org/wiki/Digestion#Digestive_hormones), including [gastrin](https://en.wikipedia.org/wiki/Gastrin), [secretin](https://en.wikipedia.org/wiki/Secretin), [cholecystokinin](https://en.wikipedia.org/wiki/Cholecystokinin), and [ghrelin](https://en.wikipedia.org/wiki/Ghrelin), are mediated through either [intracrine](https://en.wikipedia.org/wiki/Intracrine) or [autocrine](https://en.wikipedia.org/wiki/Autocrine) mechanisms, indicating that the cells releasing these hormones are conserved structures throughout [evolution](https://en.wikipedia.org/wiki/Evolution).[\[11\]](https://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-11)


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