Ileum

Structure and Function

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Structure

General

About 20ft long. The first 2 fifths are jejunum, the rest ileum. Each has distinctive features, but there is a gradual change. The jejunum begins at the duodenojejunal flexure, and the ileum ands at the eleocecal junction. The coils are freely moveable, and attached to the posterior abdominal wall by folds of peritoneum called the mesentery of the small intestine. At the root of the mesentery is the entrance and exit of the superior mesenteric artery and vein, lymph vessels and nerves.

Differences between ileum and jejunum

Area	Jejunum	Ileum
Location	Upper part of peritoneal cavity, by the left side of the transverse colon.	Lower part of cavity and in the pelvis.
Size	Wider bored, Thicker walled, and redder. Thicker walls because the plicae circulares are larger and more numerous.	Plicae circulares smaller and wider separated – absent in lower part of ileum.
Mesentery	Mesentery attached to posterior abdominal wall above and left of aorta.	Mesentery attached below and right of aorta.
Vessels	Only one or two arcades, with long branches to the wall.	Numerous short terminal vessels, after 3 or more arcades.
Fat	Fat deposited near the root, and is scanty near intestines.	Fat is deposited throughout.
Peyer's Patches	No Peyer's patches	Peyer's patches (lumps of lympoid tissue) present on the antimesenteric wall.