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Gastrointestinal tract

Last updated: August 8, 2019

Gross anatomy


Peritoneum and retroperitoneum

Layers of peritoneum

Peritoneal cavity

Epiploic foramen (foramen of Winslow)

Organs of the peritoneal cavity

Intraperitoneal organs

Secondary retroperitoneal organs

Retroperitoneal organs
Stomach Duodenum (2nd and 3rd part) Kidneys
Duodenum (1st part) Ascending colon Adrenal glands
Jejunum Descending colon Ureters
Ileum Upper rectum Aorta
Cecum/ appendix Pancreas (head, neck, body) Inferior vena cava
Transverse colon Lower rectum
Sigmoid colon Anal canal
Liver and gallbladder
Pancreas (tail)
Genital organs


The abdominal aorta is the direct continuation of the descending thoracic aorta and gives rise to all the vessels that supply the organs of the abdominal cavity.

Celiac trunk

Superior mesentery artery (SMA)

Inferior mesentery artery (IMA)

Colonic anastomosis

The splenic flexure and the rectosigmoid junction are watershed areas, which are most vulnerable to bowel ischemia.

Venous drainage of the GI tract

Portocaval anastomoses


Microscopic anatomy


The gastrointestinal tract is composed of four main layers. Although variations exist between each part of the gut, the general structure remains similar. The 4 layers are as follow:

Regional characteristics



Mucosal cells and glands

Notable features Functions

Oral cavity

  • Lubrication of food
  • Antibacterial protection
  • IgA secretion


  • Body and fundus: shallow pits, deep glands
  • Pylorus: deep pits, shallow, branched glands


  • Villi
  • Plicae
  • Crypts of Lieberkühn



  • No villi
  • Crypts of Lieberkühn
  • Active transport of Na+ and passive reabsorption of water from the intestinal lumen
Rectum and anal canal
  • Contains inner circular and outer circular muscle layers
  • Voluntary and involuntary control of defecation

Intestinal stem cells are located in the crypts of Lieberkuhn. These divide to replace all of the cells of the intestinal epithelium every 5 days.

Gastrointestinal function and regulators

Molecule Source Action Regulation

Gastric inhibitory polypeptide (GIP)

Vasoactive intestinal peptide (VIP)
  • ↑ Secretion of water and electrolytes
  • ↑ Relaxation of sphincters
Nitric oxide (NO)


Embryology of the gastrointestinal tract

The gastrointestinal tract (GIT) is derived from the primitive gut tube, which is divided into foregut, midgut, and hindgut. The epithelium arises from endoderm, which also gives rise to the parenchyma of the liver and pancreas. Although the spleen is in the peritoneal cavity, it is derived from mesoderm rather than endoderm.

The midgut herniates through the umbilical ring during the 6th week and returns to the abdominal cavity on the 10th week.

Clinical significance

Oral cavity



Small intestine

Large intestine

Liver, gallbladder, and pancreas


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