Mesentery

Overview

A thin layer of connective tissue is contained within the two layers of peritoneum and provides a passageway for lymphatics, nerves, arteries and veins to reach the viscera, allowing communication between the body wall and internal organs. Mesenteries are also important as they suspend or hold the organs in place to the posterior abdominal wall.

Those that are totally suspended in the cavity (i.e. are covered in visceral peritoneum) are known as intraperitoneal organs (such as the liver, ileum and stomach) whereas those that lie posterior to the peritoneum and are only covered by the visceral peritoneum on the anterior surface are known as retroperitoneal organs. Retroperitoneal organs include the distal part of the duodenum, abdominal aorta and pancreas.

The mesenteries also store fat as a means of padding. There are also other specialty peritoneal folds named the greater and lesser omenta derived from the original dorsal and ventral mesenteries, respectively, in development.

In the fully formed abdominal cavity, mesenteries are found dorsally and adhere the viscera to the posterior wall. There are three mesenteries, all named after their organ attachments in the abdominal cavity, as follows:

• the mesentery of the small intestine or mesentery proper,
• transverse mesocolon
• sigmoid mesocolon

Learn everything about the mesentery with our study unit. If you want to challenge yourself even further, try out our custom quiz on the peritoneum!

Mesentery proper

The mesentery of the small intestine is a large and broad fan-shaped mesentery that is attached to the jejunum and ileum of the small intestine, connecting them to the posterior abdominal wall. Superiorly, the mesentery of the small intestine is attached to the end of the duodenum/beginning of the jejunum (duodenojejunal junction) just to the left of the 2nd lumbar vertebra. It runs obliquely down to terminate and attaches at the end of the ileum/beginning of the cecum (ileocecal junction) by the right sacro-iliac joint.

The blood vessels, lymphatics and nerves that are required to supply the jejunum and ileum are found between the two layers of the peritoneum that make up the mesentery of the small intestine.

Transverse mesocolon

The transverse mesocolon is attached to the transverse colon of the large intestines, attaching it to the posterior wall. From the posterior wall, the mesentery of the transverse mesocolon lies anteriorly across the front of the head and body of the pancreas to enclose around the transverse colon. The transverse mesocolon also divides the abdominal cavity into supracolic and infracolic compartments (superior and inferior to the transverse mesocolon, respectively).

The supracolic compartment contains:

• stomach
• liver
• spleen

The infracolic compartment contains:

• small intestine
• ascending and descending colon of the large intestine

The infracolic compartment is further divided into left and right infracolic spaces by the mesentery of the small intestine. There is communication between the supracolic and infracolic compartments by the paracolic gutters.

The structures in between the peritoneal layers are the blood vessels, nerves and lymphatics that are responsible for supplying the transverse colon. The transverse mesocolon is also continuous with the greater omentum.

Sigmoid mesocolon

The sigmoid mesocolon is an inverted V-shaped attachment of the sigmoid colon of the large intestines to the abdominal wall. The apex of the V is attached by the bifurcation point of the internal and external branches of the common iliac artery. The descent of the left branch of the V-shaped sigmoid mesocolon goes along the medial border of the left psoas major muscle. The right side of the sigmoid mesocolon travels down into the pelvis, ending anteriorly around the level of the 3rd sacral vertebra.

The structures passing through the peritoneal layers are the nerves and lymphatics associated with the sigmoid colon and the sigmoid artery and the superior rectal blood vessels.

Solidify your knowledge with our quiz: