Definition of Ileum

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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.