Small intestine & ampulla
General
Anatomy


Topic Completed: 1 August 2012

Minor changes: 15 December 2020

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PubMed search: Anatomy[TI] small bowel[TIAB]

Hanni Gulwani, M.B.B.S.
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Cite this page: Gulwani H. Anatomy. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/smallbowelnormalanatomy.html. Accessed May 7th, 2021.
Definition / general
  • Small intestine extends from gastric pylorus to ileocaecal valve
  • 6 meters long, divided into duodenum, jejunum, ileum
Ampulla
  • Ampulla means flask like dilatation (spreading or stretching) of a tubular structure
  • May refer to Ampulla of Vater or portion of fallopian tube, vas deferens, semicircular canal or colon
  • Vater ("fah-ter") is German anatomist Abraham Vater (1684-1751) who first described this structure
  • Usually refers to confluence of distal common bile duct and main pancreatic duct in second portion of duodenum near pancreatic head, although in 42% of patients, ampulla is termination of common bile duct only as the pancreatic duct enters the duodenum separately next to ampulla; in these cases, ampulla may be difficult to locate or nonexistent
  • Ampulla is 1.5 cm long or less, traverses duodenal wall, opens into the duodenal lumen through (major) duodenal papilla (papilla of Vater), a 0.5 cm in diameter mucosal elevation with mucosal reduplications (valves of Santorini) that probably prevent regurgitation
  • Minor papilla, also called accessory pancreatic duct (APD) of Santorini, is 2 cm proximal and slightly anterior to major papilla
  • APD is Patent in 50% cases, pancreatic tissue is noted in 80% of cases in minor papilla (Dig Surg 2010;27:137)
  • Ampulla is surrounded by muscular fibers of sphincter of Oddi
  • Reference: Dig Surg 2010;27:90
Duodenum
  • 25 cm long, from pyloric sphincter to ligament of Treitz, mostly retroperitoneal, fixed in position
  • Common bile duct (CBD) and pancreatic duct enter second part of duodenum posteromedially at ampulla of Vater (eMedicine: Duodenal Anatomy [Accessed 9 February 2018)
Jejunum
  • 240 cm long, 40% of remainder of bowel, begins at ligament of Treitz
  • Has prominent circular mucosal folds (folds of kerckring) that increase absorptive surface
Ileum
  • 360 cm long, distal 60% of postduodenal bowel
  • Mucosa has transverse folds, prominent in proximal ileum, flat / absent at terminal ileum
Ileocecal valve
  • At end of small bowel
  • 2 lip structure containing adipose tissue and lymphoid tissue
Lymph nodes
  • Duodenum drains to portal and pyloric nodes
  • Jejunum and proximal ileum drain to mesenteric nodes and nodes around superior mesenteric artery, terminal ileum drains to ileocolic nodes
  • Lacteals are lymphatic channels in villi for chylomicrons
Intestinal immune system
  • Peyer patches in ileum (ovoid lymphoid follicles, partly mucosal and partly submucosal, in antimesenteric side of terminal ileum)
  • Small intestinal goblet cells, which deliver low molecular weight soluble antigens from intestinal lumen to CD103+ lamina propria dendritic cells, which regulates development of T cells (Nature 2012;483:345)
  • M (membranous) cells, part of follicle associated epithelia (MALT) in small bowel and colon, which transfer antigen macromolecules from lumen to lymphocytes
  • T cells, usually CD8+ and scattered in surface epithelium
  • Lamina propria contains CD4+ T cells and B cells
  • Mucosa associated lymphoid tissue: lymphoid nodules, mucosal lymphocytes, appendiceal lymphoid follicles and mesenteric nodes (Annu Rev Cell Dev Biol 2000;16:301)
Neuromuscular function
  • Anterograde and retrograde peristalsis mixes food and promotes maximal contact of nutrients with mucosa
  • Colonic peristalsis prolongs contact with mucosa
  • Peristalsis is mediated via myenteric plexus and autonomic innervation (sympathetic thoracolumbar, parasympathetic vagal)
  • Also through interstitial cells of Cajal (pacemaker cells) and smooth muscle cells
  • Vagal receptors are abundant in duodenum and scattered throughout wall
Diagrams / tables

Images hosted on other servers:

Duodenum

Local anatomy (called common duct)

Papilla

Gross images

Images hosted on other servers:

Ileum and terminal ileum

Microscopic (histologic) images

Contributed by Grigory Demyashkin, M.D., Ph.D.

6 - 8 week embryo:

Upper left: small intestine;
bottom left: esophagus;
center: stomach; top right:
pancreas; right: liver

Small intestine, epithelium

Left: small intestine; bottom:
stomach; center: gonad and
kidney primary (mesonephros);
right: symphysis



Contributed by Suhail Muzaffar, M.B.B.S.
Small intestine-normal (duodenum) Small intestine-normal (duodenum) Small intestine-normal (duodenum)

Small intestine - normal (duodenum)

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Image 01 Image 02