[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Abdomen](https://durgical.com/en/anatomy/region/abdomen/) › Ileum [Digestive system](https://durgical.com/en/anatomy/system/digestive-system/) · [Abdomen](https://durgical.com/en/anatomy/region/abdomen/) # Ileum The ileum is the last part of the small intestine, ending at the colon in the lower right belly; it absorbs vitamin B12 and bile acids. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=abdomen&select=ileum&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The last part of the small intestine, in the lower right abdomen, ending at the cecum. ## What it does Absorbs vitamin B12 and bile salts. ## Key points - Disease or resection of the terminal ileum (as in Crohn disease) causes vitamin B12 deficiency, bile-acid diarrhea and a higher risk of gallstones - Ileum vs [jejunum](https://durgical.com/en/anatomy/jejunum/): thinner, paler wall, narrower lumen, low sparse folds, many arcades with short vasa recta, more mesenteric fat and large Peyer patches on the antimesenteric border - Meckel diverticulum arises from the antimesenteric border of the ileum ## Key facts **Where** Distal three-fifths of small intestine to ileocecal junction; mostly right lower abdomen and pelvis **Blood supply** Ileal branches of SMA (many arcades, short vasa recta) and ileal branch of [ileocolic artery](https://durgical.com/en/anatomy/ileocolic-artery/) **Nerve** Vagus (parasympathetic); sympathetic via [superior mesenteric plexus](https://durgical.com/en/anatomy/superior-mesenteric-plexus/) (T8–T10) **Function** Absorbs vitamin B12 and bile salts (terminal ileum); Peyer's patches; Meckel diverticulum about 60 cm from ileocecal valve ## Relations **Course** Coils in the lower [abdomen](https://durgical.com/en/anatomy/region/abdomen/) and [pelvis](https://durgical.com/en/anatomy/region/pelvis/) down to the ileocecal junction in the right iliac fossa, entering the medial side of the [cecum](https://durgical.com/en/anatomy/cecum/) **In front** [Greater omentum](https://durgical.com/en/anatomy/greater-omentum/) and the anterior abdominal wall **Behind** Behind the parietal [peritoneum](https://durgical.com/en/anatomy/peritoneum/): right psoas, right [ureter](https://durgical.com/en/anatomy/ureter/) and the iliac vessels at the pelvic brim **Below** Pelvic organs: bladder, and uterus and [ovaries](https://durgical.com/en/anatomy/ovary/) in women; loops often lie in the rectovesical or [rectouterine pouch](https://durgical.com/en/anatomy/rectouterine-pouch/) **Lateral** Cecum and [ascending colon](https://durgical.com/en/anatomy/ascending-colon/) on the right ## How to find it At surgery it is traced back from the ileocecal junction; the ileocecal fold (bloodless fold of Treves) on the antimesenteric border near the cecum is a landmark. A Meckel diverticulum is looked for by running the distal ileum back from the cecum. ## On imaging In Crohn disease, CT or MR enterography shows thickening of the terminal ileum and the comb sign (engorged vasa recta); a barium follow-through may show the string sign of a narrowed segment. A technetium-99m pertechnetate scan (Meckel scan) detects ectopic gastric mucosa in a Meckel diverticulum. ## Common problems - Crohn disease often affects its last part. ## How it is diagnosed Examination, X-ray or CT, endoscopy, blood tests. ## Treatment - Depends on the cause: rest and fluids for many obstructions, medicines for Crohn disease, surgery for some. ## Clinical notes - Meckel diverticulum may present as painless rectal bleeding in a young child (acid from ectopic gastric mucosa ulcerates the nearby ileum), or mimic appendicitis, intussusception or obstruction - Ileocolic intussusception in infants, often with enlarged Peyer patches as the lead point after a viral illness - Gallstone ileus: a large stone that has passed through a cholecystoduodenal fistula impacts near the ileocecal valve, the narrowest part of the small bowel - Ileal tuberculosis favors the ileocecal region and can mimic Crohn disease ## Anatomical variants - Meckel diverticulum, the commonest congenital anomaly of the gut; it may contain gastric or pancreatic tissue ## Development The vitelline (omphalomesenteric) duct joins the apex of the midgut loop, the future ileum, to the yolk sac; if it fails to close it can leave a Meckel diverticulum, a fibrous cord to the umbilicus or an umbilical fistula. ## Memory aid Meckel «rule of 2s», a classic teaching aid rather than exact data: about 2% of people, about 2 feet (60 cm) from the ileocecal valve, about 2 inches long, 2 kinds of ectopic tissue (gastric, pancreatic), often symptomatic before age 2. ## Related conditions - [Small bowel obstruction](https://durgical.com/en/conditions/small-bowel-obstruction/) - [Crohn disease](https://durgical.com/en/conditions/crohn-disease/) - [Irritable bowel syndrome](https://durgical.com/en/conditions/irritable-bowel-syndrome/) - [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/) - [Acute mesenteric ischaemia](https://durgical.com/en/conditions/acute-mesenteric-ischaemia/) - [Intussusception (children)](https://durgical.com/en/conditions/intussusception/) - [Carcinoid syndrome](https://durgical.com/en/conditions/carcinoid-syndrome/) - [Lactose intolerance](https://durgical.com/en/conditions/lactose-intolerance/) - [Normal anion gap (hyperchloraemic) metabolic acidosis](https://durgical.com/en/conditions/normal-anion-gap-metabolic-acidosis/) - [Megaloblastic anaemia (B12 or folate deficiency)](https://durgical.com/en/conditions/megaloblastic-anaemia/) - [Paralytic ileus and colonic pseudo-obstruction (Ogilvie)](https://durgical.com/en/conditions/paralytic-ileus-and-colonic-pseudo-obstruction/) - [Small intestinal bacterial overgrowth (SIBO)](https://durgical.com/en/conditions/small-intestinal-bacterial-overgrowth/) - [Short bowel syndrome](https://durgical.com/en/conditions/short-bowel-syndrome/) - [Tropical sprue](https://durgical.com/en/conditions/tropical-sprue/) - [Graft-versus-host disease](https://durgical.com/en/conditions/graft-versus-host-disease/) - [Soil-transmitted helminthiasis (ascariasis, hookworm, trichuriasis)](https://durgical.com/en/conditions/soil-transmitted-helminthiasis/) - [Typhoid (enteric) fever](https://durgical.com/en/conditions/typhoid-fever/) - [Bacterial infectious diarrhoea and dysentery](https://durgical.com/en/conditions/bacterial-infectious-diarrhoea-and-dysentery/) - [Cholera](https://durgical.com/en/conditions/cholera/) - [Cryptosporidiosis and other intestinal coccidia (Cyclospora, Cystoisospora)](https://durgical.com/en/conditions/cryptosporidiosis-and-other-intestinal-coccidia/) - [Intestinal tapeworm infections (taeniasis, hymenolepiasis, diphyllobothriasis)](https://durgical.com/en/conditions/intestinal-tapeworm-infections/) - [Prematurity and its complications](https://durgical.com/en/conditions/prematurity-and-its-complications/) - [Necrotising enterocolitis](https://durgical.com/en/conditions/necrotising-enterocolitis/) - [Meckel diverticulum](https://durgical.com/en/conditions/meckel-diverticulum/) - [IgA vasculitis (Henoch–Schönlein purpura)](https://durgical.com/en/conditions/iga-vasculitis/) - [Postoperative ileus](https://durgical.com/en/conditions/postoperative-ileus/) ## Test yourself Think of the answer, then tap the question to see it. ## What does the terminal ileum absorb? Vitamin B12 and bile salts; disease or resection (as in Crohn disease) causes B12 deficiency, bile-acid diarrhea and more gallstones. ## Where does a Meckel diverticulum arise? From the antimesenteric border of the ileum, about 60 cm from the ileocecal valve; it may contain gastric or pancreatic tissue. ## How does a Meckel diverticulum classically present in a young child? Painless rectal bleeding: acid from ectopic gastric mucosa ulcerates the nearby ileum; a Meckel scan (technetium-99m pertechnetate) detects it. ## Where does a gallstone impact in gallstone ileus? Near the ileocecal valve, the narrowest part of the small bowel, after passing through a cholecystoduodenal fistula. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/ileum/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** ileum TA2 2959 **Official Spanish (DeCS)** Íleon DeCS D007082 **English (TA2)** Ileum **Also called** intestinum ileum · intestinum ilium ## Related - [Jejunum](https://durgical.com/en/anatomy/jejunum/) - [Cecum](https://durgical.com/en/anatomy/cecum/) - [Superior mesenteric artery](https://durgical.com/en/anatomy/superior-mesenteric-artery/) - [Ileocolic artery](https://durgical.com/en/anatomy/ileocolic-artery/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=7265); [Anatomy, Abdomen and Pelvis, Small Intestine](https://www.ncbi.nlm.nih.gov/books/NBK459366/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/ileum/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/ileum/