Accessory Organs - Mesentery Flashcards
What is the mesentery?
The mesentery is a double fold of peritoneum that suspends the small intestine and large intestine from the posterior abdominal wall.
Function of the mesentery?
1) Suspends the small and large intestine from the posterior abdominal wall; anchoring them in place, whilst allowing for some movement.
2) Provides a conduit for blood vessels, nerves and lymphatics.
3) Postulated to play a pathlogical role in inflammatory disease such as Crohn’s disease.
Structure?
The mesentery is formed by double-layered fold of peritoneum.
Although the mesentery is now though to be a contiguous structure, subsections of the mesentery can be named according to the viscera it is associated with. Thus, names such as mesocolon, mesorectum, mesosigmoid all relate to different parts of the mesentery.
The ‘root’ of the mesentery is the point where the mesentery attaches to the posterior abdominal wall, and is therefore a ‘bare area’. Due to the range of abdominal organs the mesentery envelopes, the root is long, narrow and has an oblique orientation, from the left side of the L2 vertebra to the right sacroiliac junction roughly.
In the GI tract, there are six flexures of note; duodenojejunal, ileocaecal, hepatic, splenic, and those between the descending and sigmoid colon and the sigmoid and rectum. These flexures are often used to mark the distinction between different portions of the mesentery:
1) Mesentery of the small intestine - connects the loops of the jejunum and ileum to the posterior abdominal wall and is a mobile structure.
2) Right mesocolon - flattened against the posterior abdominal wall.
3) Transverse mesocolon - a mobile structure and lies between the colic flexures.
4) Left mesocolon - flattened against the posterior abdominal wall.
5) Mesosigmoid - has a medial portion which is flattened against the posterior abdominal wall, whereas the region of mesentery associated with sigmoid colon itself is mobile.
6) Mesorectum - assists in anchoring the rectum through the pelvis.
The areas of the mesentery that are flattened against the posterior abdominal wall (2, 4, medial 5) are attached to the abdominal wall via an additional layer of connective tissue known as Toldt’s fascia. The fascia contains several lymphatic channels.
Clinical relevance - intestinal volvulus?
A volvulus occurs when a loop of intestine twists around itself and its mesentery, causing obstruction of the bowel. It is possible that the bowel will twist tightly enough to prevent the blood supply to the intestine, resulting in bowel infarction.
The most commonly affected area of bowel is the sigmoid colon. The risk of intestinal volvulus is increased in children with intestinal malrotation, a congenital defect in which embryological intestinal rotation is incomplete, resulting in improper anchoring of the intestines to the posterior abdominal wall.
Medical imaging (abdominal x-ray, CT abdo-pelvis) is frequently used to confirm a diagnosis, and serious cases require surgical intervention.
