Small Intestine

The small intestine, is a convoluted tube, about 6 meters long, extending from the pylorus to the ileo-cecal valve, situated centrally in the abdominal cavity and is flanked laterally and superiorly by the large intestine.

Divisions: 1. Duodenum 2. Jejunum 3. Ileum Jejunum and ileum They form the mobile part of the small intestine, suspended from the posterior abdominal wall by a mesentery.

Few and simple Numerous and complex Jejunum Ileum Length: proximal 2/5 (8 feet) distal 3/5 (12 feet) Diameter: Wide Narrow Arterial arcades: Few and simple Numerous and complex

Jejunum Ileum 4- Mesentery: Few fat,+ve windows Much fat, no windows 5. Mucosal Circular Folds: Numerous Few ( Plica Circularis)

Jejunum Ileum 6- Wall : thick thin 7- Pyer’s patches: -ve +ve

Mesentery of the small intestine: is a fan- shaped peritoneal fold which has an anterior free border and posterior attached border. The anterior border contains the jejunum and ileum and is 6 meter long. The posterior border is the root of mesentery and is 6 inches long.

Structures crossed by the root of the mesentery (6): 3rd part of duodenum Abdominal aorta and right gonadal vessels. IVC. Right psoas major. Right ureter. Right genitor-femoral nerve.

Contents of the mesentery: Superior mesenteric artery. Superior mesenteric vein. Coils of the small intestine Extraperitoneal tissue and fat. Sympathetic nerve fibers. Mesenteric LN (arranged in three groups: large, medium, and small).

Superior mesenteric artery Origin: from descending abdominal aorta 1cm below coeliac trunk at the level of lower border of L1 vertebra

Course: It is accompanied by superior mesenteric vein on its right side and both of them run in the root of mesentery.

Structures supplied by SMA: It supplies midgut .

Branches of sup. mesenteric a. inferior pancreaticoduodenal artery Supplies head of the pancreas and to the descending and inferior parts of the duodenum middle colic artery Supplies to the transverse colon right colic artery to ascending colon intestinal arteries branches to ileum, jejunum ileocolic artery (terminal branch of the SMA) supplies last part of ileum, cecum, and appendix