It is a structure that is hidden behind the skin of the belly and abdominal muscles.
This hidden structure plays a vital role in the body.
The discovery of the mesentery is not new, in fact, even Da Vinci reflected it in his anatomical drawings in the 15th century.
The mesentery continued to appear in textbooks through the 1800s and modern medicine.
Most scientists thought that what we now know as the mesentery are not separate sections of tissue scattered throughout the intestines.
In 2012, Coffey and a team of colleagues identified that it was, in fact, a continuous structure by removing layers of cells in the gut.
For four years, they continued to investigate the mesentery (as did other scientists around the world) until they gathered enough information to propose that it be considered an organ.
Currently, there are 78 organs and 13 systems that make up the human body. The mesentery is a newly classified organ in the abdomen.
Organs are typically classified by their specific structure or the function they perform.
The stomach, bladder, and kidneys are self-contained areas of tissues that work together for function.
So despite the fact that they have the same function, they are each an organ because they have different structures.
On the other hand, substances like blood are also sometimes considered an organ because, although blood circulates throughout the body and does not have a specific structure, it has a unified function: to carry oxygen to other organs and to circulate immune cells.
And although the appendix does not have a specific function, which is still known, it is considered an organ because the condition is caused by its infection, and is known as appendicitis.
The mesentery should be considered an organ because it supports the intestines, a discrete role and also has a different structure.
There is no real benefit to defining the mesentery as a separate organ.
But by defining the mesentery more specifically, it would be easier to standardize information about it, which could be used to improve abdominal surgery techniques.
Research is aimed at better understanding and finding better treatments for abdominal and digestive diseases, and reclassification is expected to help.
The mesentery, which connects the intestine to the abdomen, has been considered for hundreds of years to be a fragmented structure made up of multiple separate parts.
However, new research describes the mesentery as a continuous structure.
Better understanding and a more meticulous scientific study of the mesentery can achieve surgeries that are less invasive, with fewer complications, with rapid patient recovery, and lower overall costs.
The existence of a specific field
Mesenteric science is its own specific field of medical study today, in the same way as gastroenterology, neurology, and coloproctology.
Until recently the field of mesenteric science had not been established.
Now when the anatomy and structure of the mesentery has been established, the next step is to establish the function.
A thin layer of connective tissue is contained within the two layers of the peritoneum and provides a conduit for lymphatic vessels, nerves, arteries, and veins to reach the viscera, allowing communication between the body wall and internal organs.
The mesentery are also important as they suspend or hold the organs in place on the posterior abdominal wall.
Those that are fully suspended in the cavity (i.e. covered with visceral peritoneum) are known as intraperitoneal organs such as the liver, ileum, and stomach, while those that lie behind the peritoneum are only covered by the visceral peritoneum in the anterior part, the surface is known as retroperitoneal organs.
The retroperitoneal organs include the distal part of the duodenum, the abdominal aorta, and the pancreas.
The mesenteries also store fat as a filler medium.
There are also other special peritoneal folds called greater and lesser omenta derived from the original dorsal and ventral mesenteries, respectively, in development.
Anatomy of the mesentery
To understand the mesentery, you need to be familiar with the peritoneum. The peritoneum has two parts.
The parietal peritoneum lines the outer walls of the abdominal cavity and the visceral peritoneum is lined with the abdominal organs.
The peritoneum is a serous membrane that is highly vascular.
The mesentery is a continuation of the peritoneum that is made of connective tissue.
It secretes serous fluid, providing lubrication and decreasing friction between the abdominal organs.
The connective tissue of the mesentery contains lymphatic vessels, nerves, arteries, and veins that create a communication pathway between the abdominal wall and internal organs.
It is also responsible for keeping the abdominal organs in place.
Research provided sufficient evidence to classify the mesentery as a single, continuous organ.
The mesentery is located in your abdomen, where it surrounds your intestines.
It comes from the area in the back of your abdomen where your aorta branches into another large artery called the superior mesenteric artery.
This is sometimes known as the root region of the mesentery.
The mesentery expands from this root region to its locations throughout the abdomen.
Although the mesentery is a single structure, it has several parts:
There are two classifications of mesentery: true mesentery and specialized mesentery.
While the latter does not connect to the posterior wall, the true mesenteries connect the organs to the posterior wall of the peritoneum.
In the fully formed abdominal cavity, the mesenteries meet dorsally and attach the viscera to the posterior wall.
There are three mesenteries, all named after their attached organs in the abdominal cavity, as follows:
The true mesentery includes:
- The mesentery of the small intestine.
- El mesocolon transverse.
- The sigmoid mesentery, also known as the mesosigmoid.
The mesentery of the small intestine
The mesentery of the small intestine is a wide fan-shaped mesentery that joins the jejunum and ileum to the posterior wall of the abdomen.
It runs obliquely from the duodenojejunal junction (the point where the end of the duodenum meets the beginning of the jejunum) just to the left of the 2nd lumbar vertebra.
It runs obliquely downward to end and joins the end of the ileum with the beginning of the cecum (ileocecal junction) at the right sacroiliac joint.
The jejunum and ileum are the last two regions of the small intestine before it connects to the large intestine.
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.
The mesocolon is divided into:
This area of the mesentery runs flat along the posterior abdominal wall.
The posterior abdominal wall can be thought of as the “posterior wall” of the body cavity.
The transverse mesocolon connects the transverse colon of the large intestine with the posterior abdominal wall.
It encloses the transverse colon and divides the abdominal cavity into two compartments.
The transverse mesocolon also divides the abdominal cavity into supracholic and infracolic compartments (superior and inferior to the transverse mesocolon, respectively).
The supracolic compartment contains:
- The liver.
The infracolic compartment contains:
- Small intestine.
- The ascending colon and the 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 supracholic and infracolic compartments through the paracoic canals.
The structures between the peritoneal layers are the blood vessels, nerves, and lymphatic vessels that supply the transverse colon.
The transverse mesocolon is also continuous with the greater omentum.
The transverse colon is the largest section of the large intestine.
Like the right mesocolon, this area of the mesentery also runs flat along its posterior abdominal wall.
The sigmoid mesentery
The sigmoid mesocolon can also be called the mesosigmoid.
The sigmoid mesocolon is an inverted V-shaped insertion of the sigmoid colon from the large intestine to the abdominal wall.
The apex of the V is joined by the point of bifurcation of the internal and external branches of the common iliac artery.
The descent of the left branch of the sigmoid mesocolon in a V shape runs 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 third sacral vertebra.
The structures that traverse the peritoneal layers are the nerves and lymphatic vessels associated with the sigmoid colon and the superior and sigmoid rectal blood vessels.
This region connects the sigmoid colon to the pelvic wall. The sigmoid colon is the region of the colon that is just before the rectum.
The mesorectum, is the part of the mesentery that is connected to your rectum.
The specialized mesenteries
The specialized mesentery are also extensions of the peritoneum, but they do not attach to the back wall of the abdomen.
They are also made of connective tissue and connect organs to each other.
The specialized mesentery include the greater omentum, the lesser omentum, and the mesoappendix.
Function of the mesentery
The mesentery attaches your intestines to the wall of your abdomen.
This keeps the intestines in place, preventing it from collapsing down into the pelvic area.
If the mesentery does not form properly during fetal development, the intestines can collapse or twist.
This leads to blockage of blood vessels or death of tissues in the abdomen, which are serious conditions.
The mesentery also contains lymph nodes.
Lymph nodes are small glands found throughout the body that help fight infection.
They contain various types of immune cells and can trap pathogens, such as viruses and bacteria.
Lymph nodes in the mesentery can sample bacteria from the intestines and generate an immune response when needed.
The mesentery can also produce a protein called C-reactive protein, which is a sign of inflammation.
It is usually made in the liver, but fat cells in the mesentery can also make it.
The mesentery and Crohn’s disease
This new understanding of the mesentery and how it works could be a game changer in the way doctors understand and treat certain conditions.
Crohn’s disease is a great example of this.
Crohn’s disease is a type of inflammatory bowel disease that causes inflammation of your digestive tract and intestinal tissue.
This inflammation can lead to pain, diarrhea, and problems absorbing nutrients from food.
The mesentery of people with Crohn’s disease often has an increase in the amount and thickness of adipose tissue.
Fat cells in the mesentery can produce proteins that are associated with inflammation, including C-reactive protein.
One study linked this fatty tissue in the mesentery of people with Crohn’s disease with increased inflammation, C-reactive protein production, and bacterial invasion.
This connection suggests that targeting the mesentery could be an effective treatment option for Crohn’s disease.
For example, a probiotic therapy was shown to improve inflammation-related dysfunction in mesentery tissue samples from people with Crohn’s disease.
Also, removing part of the mesentery can be an effective way to reduce the chance of Crohn’s disease coming back after bowel resection.
Mesenteric fibromatosis is a rare occurrence that involves a benign fibrous lesion found in the mesentery of the small intestine or in the retroperitoneum.
Like other fibromatoses, it does not metastasize, but it can spread locally.
It can occur as a primary mesenteric fibromatosis or it can arise from factors that predispose a person to mesenteric fibromatosis, such as trauma, Gardener syndrome, or long-term estrogen intake.
Patients with mesenteric fibromatosis present with an abdominal mass that is often accompanied by weight loss and pain.
Treatment of mesenteric fibromatosis generally consists of surgical removal, which often involves resection of the small intestine and associated mesentery.
Intestinal volvulus (where a part of the intestine twists around the root of the mesentery) can be caused by mesenteric defects during the formation of the midgut, which then becomes the intestine.
During development, there are three stages in intestinal rotation.
First, the embryonic intestine begins as a straight tube and then begins to bend, forming an S shape that protrudes from the abdominal cavity.
During the second stage, the midgut returns to the abdominal cavity as the size of the fetus’ body reaches its size, and as a result, the intestine completes a 270 ° turn counterclockwise giving it the final orientation in the peritoneum.
In the last stage, there is little rotation but this stage is important as this is when the mesentery fuses with the posterior abdominal wall.
This allows the small intestine to develop into a wide secondary attachment along the root of the mesentery.
There are two main types of mesenteric defects that can occur:
Where the base of the mesentery is involved and does not fuse in the third stage.
It only affects isolated parts of the mesentery, but both can cause volvulus.
The severity of symptoms depends on the extent of the defect and the amount of small intestine that is involved in the volvulus, but it can lead to intestinal obstruction and intestinal atresia.