The peritoneum is a large membrane that surrounds and supports many of the abdominal organs. A double fold of this membrane comprises the mesentery. This is the tissue that attaches the intestines to the abdominal wall. Additionally, the mesentery helps store fat and allows blood vessels, lymphatics, and nerves to reach and supply the intestines. It also has many structures within it, and each carries different responsibilities. These include various mesocolon regions, small-intestine mesentery, mesoappendix, and mesorectum.
Advancements in technology allowed new microscopic examinations that led to an innovative discovery in 2012. Several structures which experts believed to be separate parts of the digestive system were actually one unified mass. A 2016 article provided enough evidence for the medical community to recognize this mass as an organ. Experts dubbed it the mesentery and the most well-known textbook, Gray’s Anatomy, added it to their latest edition in 2016. This discovery led to many innovations in various medical fields.
The mesentery surrounds the intestines in the abdomen. It begins in the back of the abdomen, where the aorta of the heart meets with a large artery. This artery is the superior mesenteric artery experts sometimes refer to as the root of the mesentery. This root marks the beginning of the mesentery as it reaches from this area throughout the rest of the abdomen. The various regions of the mesocolon connect to the colon itself. The mesoappendix connects the ileum of the small intestine to the appendix. The mesorectum attaches to the rectum.
The root connects the jejunum and ileum regions of the small intestine to the posterior abdominal wall. These are the two areas of the small intestine just before where the organ connects with the large intestine. The root is about 15 centimeters long and sits centrally in the abdominal cavity, behind the transverse colon. When the mesentery attaches to the colon at the gastrointestinal margin, it becomes the regions of the mesocolon.
The right mesocolon and left mesocolon are flat structures that sit along the posterior abdominal wall. The transverse mesocolon is a broad portion of peritoneum that connects the transverse colon to the same abdominal wall. The transverse colon is the longest portion of the large intestine. Another fold of peritoneum connects the sigmoid colon to the pelvic wall. This is the sigmoid mesocolon. The sigmoid colon is a continuation of the colon that enters the pelvis.
A fold of peritoneum attaches to the lower portion of the small intestine's mesentery and stretches around the appendix to reach its tip. This is the mesoappendix that contains the artery and veins that supply blood to the appendix. The mesorectum is the portion of the mesentery that attaches to the upper portion of the rectum. It is a fatty tissue that contains blood vessels, lymph vessels, lymph nodes, and nerves from the autonomic portion of the nervous system.
Though researchers are still studying the exact purposes of the mesentery, they have determined some of its more obvious functions. The various structures of the mesentery connect portions of the intestines to the posterior abdominal wall, holding the intestines in place. This provides support for the organs and prevents them from collapsing into the pelvis. Collapsed intestines as a result of a malformed or damaged mesentery can result in blocked blood vessels and tissue necrosis. Typically, the liver produces C-reactive protein in response to inflammation, but the fatty tissue in the mesentery can produce it as well.
Some individuals may wonder why experts only recently discovered this. Anatomists have known about this part and its structures for centuries. Sir Frederick Treves wrote about the mesocolon in 1885, and Leonardo da Vinci suggested that the membrane was a singular entity centuries before that. Various doctors over the years echoed the idea that the structures were a single organ, but the medical community largely ignored these claims. It wasn’t until researchers conducted a formal appraisal in 2012 that they identified the mesentery as a contiguous organ that spanned through the abdominal cavity.
By discovering the singular nature of the mesentery, researchers opened the doors to new understanding. There is now clearer comprehension of conditions such as intestinal malrotation and Crohn’s disease. Surgeons and doctors can now differentiate between the mesocolon connections from scar tissue that attach to otherwise separated tissues. Additionally, understanding the attachment between the mesocolon regions and other tissue allow for access to the cells hidden within.
In the past, because the medical community held the belief the mesentery was several unrelated structures, radiologists weren’t able to make conclusions about certain diseases. For example, when studying the spread of colon cancer, researchers found that many patients developed bulges in their intestine called diverticula. With the knowledge that the mesentery is a single organ, researchers were able to find previously unknown links. It also led to revelations about fluid collections in patients with pancreatitis.
Doctors have found new insights into Crohn’s disease through the classification of the mesentery as a singular organ. Crohn’s disease is a complex inflammatory bowel disease that can affect any portion of the gastrointestinal tract. The cause of this disease is still unknown. However, Crohn’s disease causes the mesentery to thicken, resulting in fat wrapping around the gastrointestinal tract. This suggests there is a connection between the mesentery and Crohn’s disease, whereas researchers used to believe the mesentery structures were merely bystanders. This may lead to important breakthroughs in treating the currently incurable disease.
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