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Small intestine & ampulla

General

Anatomy

Author: Hanni Gulwani, M.B.B.S.

Last author update: 1 August 2012

Last staff update: 24 July 2023

Copyright: 2003-2024, PathologyOutlines.com, Inc.

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

Table of Contents

Cite this page: Gulwani H. Anatomy. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/smallbowelnormalanatomy.html. Accessed December 24th, 2024.

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

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