Mesentery

The mesentery is the broad, fan-shaped fold of peritoneum which connects the convolutions of the jejunum and ileum with the posterior wall of the abdomen.

The root of the mesentery (the part connected with the structures in front of the vertebral column) is narrow, about 15 cm long, and is directed obliquely from the duodenojejunal flexure at the left side of the second lumbar vertebra to the right sacroiliac articulation.

The intestinal border of the mesentery is about 6 metres long; and here the two layers separate to enclose the intestine, and form its peritoneal coat. It is narrow above, but widens rapidly to about 20 cm, and is thrown into numerous plaits or folds. It suspends the small intestine, and contains between its layers the intestinal branches of the superior mesenteric artery, with their accompanying veins and plexuses of nerves, the lacteal vessels, and mesenteric lymph glands.

The term mesentery proper concerns the double layer of peritoneum that suspends the jejunum and ileum from the posterior wall of the abdomen but its meaning, however, is frequently extended to include double layers of peritoneum connecting various components of the abdominal cavity.

Since 2012, new approach consider the mesentery as a single structure. This structure, termed "mesenteric organ", is continuous from duodenojejunal flexure to mesorectum, spanning the gastrointestinal tract between. Recent histologic findings have demonstrated that although apposed to the retroperitoneum, the mesenteric organ is separated from this via Toldt’s fascia. The different parts of the mesenteric organ are:

• The mesentery of the small bowel (mesentery proper) is the part of mesenteric organ attached to the small intestine or mesentery proper

• The mesocolon is the part of mesenteric organ attachend to the colon, including the transverse, ascending, descending, and sigmoid mesocolon

• The mesoappendix is the part of mesenteric organn of the mesentery connecting the ileum to the appendix. It may extend to the tip of the appendix. It encloses the appendicular artery and vein, as well as lymphatic vessels, nerves, and often a lymph node.

• The mesorectum is the part of mesenteric organ attached to the upper third of the rectum.