Together are approximately 6 m long
The mesentery
Double layered fold of peritoneum
Attaches jejunum and ileum to posterior abdominal wall
Root of mesentery
Follows an oblique line
Runs inferiorly and to the right, from ligament of Treitz to ileocolic junction
Between two layers are SMA, SMV, lymph nodes, fat, and autonomic nerves
Jejunum
Approximately two fifths of the length
Mainly in the left upper quadrant (LUQ)
Thick-walled and very vascular
Ileum
Approximately three fifths of the length
Mainly in the right lower quadrant (RLQ)
Thin-walled and less vascular
Terminates at the ileocecal junction
Vascular supply (Section 4-6: Abdomen-Visceral Vasculature)
Arteries
Superior mesenteric artery
Fifteen to 18 branches from SMA to jejunum and ileum
Branches unite to form loops or arches (arterial arcades)
Arcades give rise to straight arteries = vasa recta
Double row of arcades to ileum
Veins
SMV drains ileum and jejunum
Posterior to neck of pancreas joins splenic vein to form portal vein
Lymphatics
Specialised lymphatic vessels that absorb fat = lacteals
Absorbed fat = chyle
Lacteals found in villi (finger-like projections of intestinal mucosa)
Lacteals drain to lymphatic plexuses in walls of jejunum and ileum
Lymphatics pass between the layers of the mesentery to mesenteric lymph nodes and then to superior mesenteric or
ileocolic nodes
Lymph drains to cisterna chyli
Innervation (Section 4-7: Abdomen-Innervation)
Parasympathetic supply
Preganglionic fibers from the posterior vagal trunks
Synapse on postganglionic cells in myenteric and submucosal plexuses in intestinal wall
Sympathetic supply
Preganglionic fibers from T5-T9 spinal cord segments → sympathetic trunks → greater and lesser splanchnic nerves
Synapse on postganglionic cells in celiac and superior mesenteric gangliaLarge intestine (colon)