Mesentery

The mesentery is a double-layered peritoneal structure that anchors the small intestine (jejunum and ileum) to the dorsal body wall, allowing movement while maintaining connection to blood vessels, lymphatics, and nerves.

When "mesentery" is used without specification, it typically refers to the mesojejunum and mesoileum together (the great mesentery, mesenterium commune).

But as the mesentery as a whole originates from the dorsal mesogastrium in the embryo and divides into regional mesenteries as the gut elongates and rotates, new approaches consider the mesentery as a single structure. This structure, termed "mesenteric organ", is continuous from duodenojejunal flexure to mesorectum, spanning the gastrointestinal tract between. The term "mesentery" then can encompass several named folds associated with different parts of the intestine:

• Mesoduodenum – suspends the duodenum.

• Mesojejunum – supports the jejunum.

• Mesoileum – supports the ileum.

• Mesocolon – supports the colon.

• Mesorectum – supports the rectum.

Root of the Mesentery (Radix Mesenterii)

• Fixed point where the mesentery attaches to the dorsal abdominal wall, near the second lumbar vertebra.

• Approximately 3–6 cm long (species dependent).

• Point of passage for major vessels: cranial mesenteric artery, vein, and mesenteric lymph nodes.

Fan-Shaped Expansion

• From the root, the mesentery expands ventrally and caudally, enveloping the small intestine.

• The jejunum and ileum are suspended by the expanded edge of this fan.

Contents

• Arteries: Branches of the cranial mesenteric artery, supplying the intestines.

• Veins: Draining into the portal vein.

• Lymphatics: Include prominent jejunal and ileal lymph nodes.

• Nerves: Sympathetic and parasympathetic fibers traveling in mesenteric plexuses.

• Adipose tissue: Especially in adult animals or obese patients.

Species Differences