The ileum is the last and longest part of the small intestine, making up about three-fifths of the bowel beyond the duodenum and ending at the ileocaecal junction. It lies mostly in the lower right abdomen and pelvis. It has a thinner wall, fewer and lower circular folds, short vasa recta, multiple arterial arcades and many lymphoid nodules grouped as Peyer patches.
| Location | Mostly in the right lower quadrant and pelvis, from the jejunum to the ileocaecal junction |
|---|---|
| Parts |
|
| Nerve Supply | Vagus nerve (parasympathetic); Superior mesenteric plexus, from lesser splanchnic nerves (sympathetic) |
| Blood Supply | Ileal arteries (from the superior mesenteric artery); Ileocolic artery |
| Venous drainage |
|
| Lymphatic drainage |
|
Absorbs remaining nutrients, vitamin B12 and bile acids for recycling to the liver, and plays a major role in gut immune surveillance.
The terminal ileum is the only site where vitamin B12 (bound to intrinsic factor) and most bile acids are absorbed, so disease or resection here causes B12 deficiency, bile acid diarrhoea and gallstones. It is the classic site of Crohn disease. A Meckel diverticulum, present in about 2 percent of people, arises from its antimesenteric border usually within about 60 cm of the ileocaecal valve.
Inflammation of the last part of the ileum, most often from Crohn disease, causing right lower abdominal pain, diarrhoea and weight loss.
Remnant of the vitellointestinal duct on the ileum that may contain gastric lining and cause painless rectal bleeding, obstruction or inflammation.
Obstruction of the narrow terminal ileum by a large gallstone that has entered the bowel through a fistula.
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