Ileum

The lowest part of the small intestine, located beyond the duodenum and jejunum, just before the large intestine (the colon). Pronounced "il-eum" in the US and "eye-leum" in the UK. The word "ileum" is derived from the Greek "eileos" meaning "twisted." This is apt because, when the small intestine is viewed at surgery or at autopsy (or exposed from a wound), it looks twisted. It is also apt because, when the small intestine is obstructed, the ileum is most often the site of the twist or whatever is causing the obstruction. The ileum is not to be confused with the ilium, the upper part of the pelvis which forms the receptacle for the head of the femur at the hip joint.

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The third and longest portion of the small intestine, about 12 feet in length in humans, extending from an indistinct junction with the jejunum to the ileocecal opening. Overall, it is distinct from jejunum in being typically smaller in diameter with thinner walls, having smaller and less complex circular folds (plicae circulares), its mesentery having more fat and its arteries (ileal arteries) forming more tiers of arterial arcades with shorter vasa recta. [L. fr. G. eileo, to roll up, twist]

- i. duplex tubular or cystic segmental duplications of alimentary tract.

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il·e·um 'il-ē-əm n, pl il·ea -ē-ə the last division of the small intestine that constitutes the part between the jejunum and large intestine and in humans forms the last three fifths of the part of the small intestine beyond the end of the duodenum and that is smaller and thinner-walled than the jejunum with fewer circular folds but more numerous Peyer's patches

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n.

the lowest of the three portions of the small intestine. It runs from the jejunum to the ileocaecal valve.

• ileal • leac adj.

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il·e·um (ilґe-əm) [L.] [TA] the distal and longest portion of the small intestine, extending from the jejunum to the cecum. ileal adj