Gastrointestinal system

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The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which ingests, digests, and egests food, and in the process, extracts energy and nutrients. (1)


Longitudinal folding of the primitive gut


Due to folding, endoderm lining the yolk sac is incorporated into the embryo as the primitive gut tube. Initially, the midgut maintains a connection with the yolk sac via the yolk stalk (vitelline duct), but later, both the yolk sac and the vitelline duct usually disappear. The mesentery helps keep everything in place.

Derivatives and blood supply

The table below is a summary of the derivatives (and arterial supply) of the caudal foregut, midgut and hindgut.

Derivatives of the primitive gut
Gut Derivatives Artery
Foregut proximal oral cavity, pharynx, upper esophagus, respiratory tract Various
distal lower esophagus, stomach, small intestine (prox. 1/2 duodenum) liver, gall bladder, pancreas coeliac
Midgut small intestine (distal 1/2 duodenum, jejunum, ileum), large intestine (caecum, appendix, ascending colon, prox. 2/3 transverse colon) superior mesenteric
Hindgut large intestine (distal a transverse colon, descending colon, sigmoid colon, rectum, anal canal) inferior mesenteric
Organization of the GI tract



The gastrointestinal tract has several main layers, which are common to the various parts:

  • Mucosa
  • Submucosa
  • Muscularis Externa
  • Serosa/Adventitia

For more in-depth histology, see: