Ileum

Last revised by Jeremy Jones on 28 Jul 2023

The ileum (plural: ilea) is the final part of the small intestine, following the duodenum and jejunum.

The ileum is not to be confused with the ilium - the associated plural/adjectival forms are ilea/ileal and ilia/ilial respectively. The plural form "ileums" is seen but is generally felt to be incorrect.

The ileum is 2-4 m in length and is separated from the cecum by the ileocecal valve (ICV). While there is no discrete line demarcating the jejunum from the ileum, there are a few differences between the two:

  • ileal mesentery contains more fat than jejunal mesentery

  • ileum tends to be smaller caliber than jejunum

  • ileum tends to be lighter in color than the jejunum

  • ileum contains abundant Peyer patches

    • Peyer patches are unencapsulated lymphoid nodules that contain large amounts of lymphocytes and other cells of the immune system

    • Peyer patches are only found on the antimesenteric border 3

  • drain to superior mesenteric lymph nodes

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Cases and figures

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