Gastrointestinal tract

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:

  • Mucosa
    • Epithelium: contains glands that aid in digestion
    • Lamina propria: attachment site for epithelial cells
    • Muscularis mucosae
  • Submucosa: contains the Meissner plexus (submucous)
    • Provides parasympathetic innervation to glands
    • Responsible for the secretomotor activity of the GIT
  • Muscularis externa: contains the Auerbach plexus (myenteric)
  • Serosa or adventitia: composed of the visceral peritoneum

Regional characteristics



Mucosal cells and glands

Notable features Functions

Oral cavity

  • Lubrication of food
  • Antibacterial protection
  • IgA secretion
  • Nonkeratinized stratified squamous epithelium
  • Transition zone
  • Skeletal muscle in upper third
  • Smooth muscle in lower third


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


  • Villi
  • Plicae
  • Crypts of Lieberkühn


  • Secretions
    • Lysozyme
    • Cholecystokinin (CCK)
    • Secretin


  • Endocytosis of antigens and transport to lymphoid tissue
  • 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)

  • Insulin secretion
  • ↓ Secretion of gastric acid
  • ↑ Intestinal motility (migratory motor complexes)
  • ↑ During fasting
Vasoactive intestinal peptide (VIP)
  • ↑ Secretion of water and electrolytes
  • ↑ Relaxation of sphincters
Nitric oxide (NO)
  • ↑ Relaxation of smooth muscle and sphincters (e.g., LES)


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

  • 1. Weerakkody Y, D'Souza D. Abdominal Aorta. Updated January 1, 2018. Accessed November 25, 2018.
  • Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences; 2016.
  • Chawla J. Autonomic Nervous System. In: Ramachandran TS. Autonomic Nervous System. New York, NY: WebMD. Updated June 28, 2016. Accessed June 7, 2018.
  • Olszewski PK, Li D, Grace MK, Billington CJ, Kotz CM, Levine AS. Neural basis of orexigenic effects of ghrelin acting within lateral hypothalamus. Peptides. 2003; 24(4): pp. 597–602. pmid: 12860204.
  • Liddle RA. Ghrelin. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. Last updated July 7, 2017. Accessed November 24, 2018.
  • Meza-Perez S, Randall TD. Immunological Functions of the Omentum. Trends Immunol. 2017; 38(7): pp. 526–536. doi: 10.1016/
  • Liao DH, Zhao JB, Gregersen H. Gastrointestinal tract modelling in health and disease. World journal of gastroenterology. 2009; 15(2): pp. 169–76. pmid: 19132766.
  • Squire L. Enteric Nervous System: Physiology. Elsevier; 2009: pp. 1103–1113.
  • Schuster MM, Crowell MD, Koch KL. Myoelectrical and contractile activities of gastrointestinal tract. London: B.C. Decker publications; 2002: pp. 1–18.
  • Lanas A. Role of nitric oxide in the gastrointestinal tract. Arthritis Res Ther. 2008; 10(Suppl 2): p. S4. doi: 10.1186/ar2465.
last updated 11/16/2020
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