Human gastrointestinal tract

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"Intestine" and "Alimentary canal" redirect here. For the animal alimentary canal in general, see Gut (anatomy).
Human gastrointestinal tract (Digestive System)
Stomach colon rectum diagram-en.svg
Stomach colon rectum diagram
Latin Tractus digestorius (mouth to anus),
canalis alimentarius (esophagus to large intestine),
canalis gastrointestinales (stomach to large intestine)
System Digestive system
Anatomical terminology

The human gastrointestinal tract, or GI tract, is an organ system responsible for consuming and digesting foodstuffs, absorbing nutrients, and expelling waste.

The tract consists of the stomach and intestines, and is divided into the upper and lower gastrointestinal tracts.[1] However, by the broadest definition, the GI tract includes all structures between the mouth and the anus.[2] On the other hand, the digestive system is a broader term that includes other structures, including the digestive organs and their accessories.[3] The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment.

The whole digestive tract is about nine metres long.[4]




Upper gastrointestinal tract[edit]

Main articles: Esophagus, Stomach and duodenum
Upper and Lower human gastrointestinal tract

The upper gastrointestinal tract consists of the esophagus, stomach, and duodenum.[7] The exact demarcation between the upper and lower tracts is the suspensory ligament of the duodenum (also known as the Ligament of Treitz). This delineates the embryonic borders between the foregut and midgut, and is also the division commonly used by clinicians to describe gastrointestinal bleeding as being of "upper" or "lower" origin. Upon dissection, the duodenum may appear to be a unified organ, but it is divided into four segments based upon function, location, and internal anatomy. The four segments of the duodenum are as follows (starting at the stomach, and moving toward the jejunum): bulb, descending, horizontal, and ascending. The suspensory ligament attaches the superior border of the ascending duodenum to the diaphragm.

The suspensory muscle of duodenum is an important anatomical landmark which shows the formal division between the duodenum and the jejunum, the first and second parts of the small intestine, respectively.[8] This is a thin muscle which is derived from the embryonic mesoderm.

Lower gastrointestinal tract[edit]

The lower gastrointestinal tract includes most of the small intestine and all of the large intestine.[9] In human anatomy, the intestine (or bowel, hose or gut) is the segment of the gastrointestinal tract extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine. In humans, the small intestine is further subdivided into the duodenum, jejunum and ileum while the large intestine is subdivided into the cecum, colon, rectum, and anal canal.[10][11]

Small intestine[edit]

Main article: Small intestine

The small intestine begins at the duodenum, which receives food from the stomach. It is a tubular structure, usually between 6 and 7 m long.[12] The area of the human, adult small intestinal mucosa is about 30 m2 (Helander HF, Fändriks L. Surface area of the digestive tract – revisited. Scand J Gastroenterol 49: 681-9, 2014.)Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. It has three major divisions:

  1. Duodenum: A short structure (about 20-25 cm long [12]) which receives gastric chyme from the stomach, together with digestive juices from the pancreas (digestive enzymes) and the gall bladder (bile). The digestive enzymes break down proteins and bile and emulsify fats into micelles. The duodenum contains Brunner's glands, which produce a mucus-rich alkaline secretion containing bicarbonate. These secretions, in combination with bicarbonate from the pancreas, neutralizes the stomach acids contained in gastric chyme.
  2. Jejunum: This is the midsection of the small intestine, connecting the duodenum to the ileum. It is about 2.5 m long, and contains the plicae circulares, and villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here.

Large Intestine[edit]

Main article: Large intestine

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

  1. Ascending colon (ascending in the back wall of the abdomen)
  2. Transverse colon (passing across the back wall)
  3. Descending colon (descending down the left side of the abdomen)
  4. Sigmoid Flexure

The main function of the large intestine is to absorb water. The area of the human, adult large intestinal mucosa is about 2 m2 (Helander HF, Fändriks L. Surface area of the digestive tract – revisited. Scand J Gastroenterol 49: 681-9, 2014.)



During fetal life, the primitive gut can be divided into three segments: foregut, midgut, and hindgut. Although these terms are often used in reference to segments of the primitive gut, they are also used regularly to describe components of the definitive gut as well.

Each segment of the gut gives rise to specific gut and gut-related structures in later development. Components derived from the gut proper, including the stomach and colon, develop as swellings or dilatations namy 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 general develop as out-pouchings of the primitive gut. The blood vessels supplying these structures remain constant throughout development.[13]

Part Part in adult Gives rise to Arterial supply
celiac trunk


Main article: Gastrointestinal wall
General structure of the gut wall
  • 1: Mucosa: Epithelium
  • 2: Mucosa: Lamina propria
  • 3: Mucosa: Muscularis mucosae
  • 4: Lumen
  • 5: Lymphatic tissue
  • 6: Duct of gland outside tract
  • 7: Gland in mucosa
  • 8: Submucosa
  • 9: Glands in submucosa
  • 10: Meissner's submucosal plexus
  • 11: Vein
  • 12: Muscularis: Circular muscle
  • 13: Muscularis: Longitudinal muscle
  • 14: Serosa: Areolar connective tissue
  • 15: Serosa: Epithelium
  • 16: Auerbach's myenteric plexus
  • 17: Nerve
  • 18: Artery
  • 19: Mesentery

The gastrointestinal tract has a form of general histology with some differences that reflect the specialization in functional anatomy.[14] The GI tract can be divided into four concentric layers in the following order:



  • 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



Main article: Submucosa

The submucosa consists of a dense irregular layer of connective tissue with large blood vessels, lymphatics, and nerves branching into the mucosa and muscularis externa. It contains Meissner's plexus, an enteric nervous plexus, situated on the inner surface of the muscularis externa.

Muscularis externa[edit]

The muscularis externa consists of an inner circular layer and a longitudinal outer muscular layer. The circular muscle layer prevents food from traveling backward and the longitudinal layer shortens the tract. The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch.


Between the two muscle layers are the myenteric or Auerbach's plexus. This controls peristalsis. Activity is initiated by the pacemaker cells (interstitial cells of Cajal). The gut has intrinsic peristaltic activity (basal electrical rhythm) due to its self-contained enteric nervous system. The rate can of course be modulated by the rest of the autonomic nervous system.

Adventitia and serosa[edit]

Main articles: Serous membrane and Adventitia





Main article: Digestion

The time taken for food or other ingested objects to transit through the gastrointestinal tract varies depending on many factors, but roughly, it takes less than an hour after a meal for 50% of stomach contents to empty into the intestines and total emptying of the stomach takes around 2 hours. Subsequently, 50% emptying of the small intestine takes 1 to 2 hours. Finally, transit through the colon takes 12 to 50 hours with wide variation between individuals.[15][16]

Immune function[edit]

Immune barrier[edit]

The gastrointestinal tract is also a prominent part of the immune system.[17] The surface area of the digestive tract is estimated to be the surface area of a football field. With such a large exposure, the immune system must work hard to prevent pathogens from entering into blood and lymph.[18][WP:V]

The low pH (ranging from 1 to 4) of the stomach is fatal for many microorganisms that enter it. Similarly, mucus (containing IgA antibodies) neutralizes many of these microorganisms. Other factors in the GI tract help with immune function as well, including enzymes in saliva and bile. Enzymes such as Cyp3A4, along with the antiporter activities, also are instrumental in the intestine's role of detoxification of antigens and xenobiotics, such as drugs, involved in first phase metabolism.

Health-enhancing intestinal bacteria of the gut flora serve to prevent the overgrowth of potentially 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% beneficial to 15-20% potentially harmful bacteria generally is considered normal within the intestines. Microorganisms also are kept at bay by an extensive immune system comprising the gut-associated lymphoid tissue (GALT).

Immune system homeostasis[edit]


Intestinal flora[edit]


Clinical significance[edit]






Several symptoms are used to indicate problems with the gastrointestinal tract:


Various methods of imaging the gastrointestinal tract are used:


  • Celiac Disease
  • Cholera
  • Diarrhoea
  • Enteric duplication cyst
  • Giardiasis
  • Irritable bowel syndrome
  • Pancreatitis
  • Peptic ulcer disease
  • Yellow Fever
  • Helicobacter pylori is a gram-negative spiral bacterium. Over half the world's population infected, mainly during childhood, it is not certain as to how the disease is transmitted. It colonizes the gastrointestinal system, predominantly the stomach. The bacterium has specific survival conditions that our gastric microenvironment: it is both capnophilic and microaerophilic. Helicobacter also exhibits a tropism for gastric epithelial lining and the gastric mucosal layer about it. Gastric colonization of this bacterium triggers a robust immune response leading to moderate to severe inflammation. This inflammatory response triggers a cascade of mucosal changes that can persist from chronic gastritis, duodenal cancer, metaplasia, dysplasia, carcinoma, to mucosal associated lymphoid tissue lymphoma (MALT lymphoma). Many individuals go through life without realizing they are infected because they were exposed young and their body sees it as normal flora. However, signs and symptoms are gastritis, burning abdominal pain, weight loss, loss of appetite, bloating, burping, nausea, bloody vomit, and black tarry stools. Infection is easy enough to detect: GI X-rays, endoscopy, blood tests for anti-Helicobacter antibodies, a stool test, and a urease breath test (which is a by-product of the bacteria.) Luckily if caught soon enough there is a treatment: it is three doses of different proton pump inhibitors as well as two antibiotics and it takes about a week to cure. If not caught soon enough surgery may be required. [21][22][23][24]
  • Ileus is a blockage of the intestines.
  • Angiodysplasia of the colon
  • Chronic functional abdominal pain
  • Constipation
  • Diarrhea
  • Hirschsprung's disease (aganglionosis)
  • Intussusception
  • Polyp (medicine) (see also Colorectal polyp)
  • Pseudomembranous colitis
  • Ulcerative colitis and toxic megacolon

In other animals[edit]

Animal intestines have multiple uses. From each species of livestock that is a source of milk, a corresponding rennet is obtained from the intestines of milk-fed calves. Pig and calf intestines are eaten, and pig intestines are used as sausage casings. Calf intestines supply Calf Intestinal Alkaline Phosphatase (CIP), and are used to make Goldbeater's skin.

Additional images[edit]

See also[edit]



  1. ^ "gastrointestinal tract" at Dorland's Medical Dictionary
  3. ^ "digestive system" at Dorland's Medical Dictionary
  4. ^ Kong F, Singh RP (June 2008). "Disintegration of solid foods in human stomach". J. Food Sci. 73 (5): R67–80. doi:10.1111/j.1750-3841.2008.00766.x. PMID 18577009. 
  6. ^ "Length of a Human Intestine". Retrieved 2 September 2009. 
  17. ^ Richard Coico, Geoffrey Sunshine, Eli Benjamini (2003). Immunology: a short course. New York: Wiley-Liss. ISBN 0-471-22689-0. 
  18. ^ Animal Physiology textbook
  21. ^ Fox, James; Timothy Wang (January 2007). "Inflammation, Atrophy, and Gastric Cancer". Journal Of Clinical Investigation. review 117 (1): 60–69. doi:10.1172/JCI30111. PMC 1716216. PMID 17200707. Retrieved 19 May 2014. 
  25. ^

External links[edit]