Organ
Ileum
Distal mobile bowel with specialized absorptive and immune roles
High-yield
The terminal ileum is the principal site for intrinsic-factor-dependent vitamin B12 uptake and active recovery of conjugated bile acids. This does not exclude small passive absorption by other routes.
Overview
Ileal loops continue gradually from the jejunum and usually occupy more of the lower abdomen and pelvis. Compared with proximal loops, they tend to have less prominent circular folds and more conspicuous lymphoid aggregates. The terminal segment enters the cecum through the ileocecal junction.
Reference facts
- Location
- Mobile mesenteric small bowel, commonly concentrated in the lower right abdomen and pelvis.
- Parts
- Continues from jejunum without a visible boundary; distal ileum ends at the cecum, and Peyer patches are especially prominent toward its antimesenteric aspect.
- Blood supply
- Ileal branches of the superior mesenteric artery and the ileal branch of the ileocolic artery; distal arcades are generally more numerous with shorter vasa recta.
- Innervation
- Superior mesenteric sympathetic pathways, vagal parasympathetic fibers and extensive enteric innervation.
- Venous/Lymphatic drainage
- Ileal veins reach the superior mesenteric vein; lymph travels through mesenteric nodes toward the superior mesenteric group.
- Relations
- Often has more mesenteric fat reaching the bowel edge than jejunum; pelvic loops change position with organ filling and mobility.
- Function
- Absorbs remaining nutrients and fluid, actively retrieves bile acids, absorbs intrinsic-factor-bound B12 and supports mucosal immune surveillance.
Clinical correlation
Terminal ileal disease or resection can impair B12 uptake and bile-acid recycling. Depending on the extent, consequences may include bile-acid diarrhea or depletion of the bile-acid pool with fat malabsorption; these outcomes are not identical in every patient.
Frequently asked questions
Where is the ileum located?
The ileum lies mobile mesenteric small bowel, commonly concentrated in the lower right abdomen and pelvis.
What does the ileum do?
Absorbs remaining nutrients and fluid, actively retrieves bile acids, absorbs intrinsic-factor-bound B12 and supports mucosal immune surveillance.
What are the parts of the ileum?
Continues from jejunum without a visible boundary; distal ileum ends at the cecum, and Peyer patches are especially prominent toward its antimesenteric aspect.
What is the blood supply of the ileum?
Ileal branches of the superior mesenteric artery and the ileal branch of the ileocolic artery; distal arcades are generally more numerous with shorter vasa recta.