Anatomists can now add a newly-recognised organ to the list of 78 organs that have previously been identified in the human body – the humble mesentery.

“Distinctive anatomical and functional features have been revealed that justify designation of the mesentery as an organ,” wrote authors of the study John Calvin Coffey, a colorectal surgeon from the University of Limerick and D. Peter O’Leary, a surgeon from the Beaumont Hospital.

“Accordingly, the mesentery should be subjected to the same investigatory focus that is applied to other organs and systems.”

Mesentery: Still the same, but different

The mesentery, a double-fold of peritoneal appendage that maintains the structural position of the stomach, intestines and other organs in the abdominal cavity, was first depicted by Leonardo Da Vinci in 1508, whose illustration demonstrated that it was a continuous structure that converged centrally.

This visualisation of the mesentery as a contiguous structure continued until 1885, when Sir Frederick Treves, a surgeon from the London Hospital, concluded that the ascending and descending colon do not have an associated mesentery, thus regarding the mesentery as several fragmented segments.

As a result, the possibility of the mesentery as an organ was overlooked, because organs are typically categorised as continuous structures that provide vital functions to the body.

However, by exposing the mesentery in specific manners and through repeated observations of the anatomical organisation, Coffey and his team were able to unveil that the mesentery was indeed a single, continuous structure.

"In the paper, which has been peer reviewed and assessed, we are now saying we have an organ in the body which hasn’t been acknowledged as such to date,” according to Coffey.

“The anatomic description that had been laid down over 100 years of anatomy was incorrect. This organ is far from fragmented and complex. It’s simply one continuous structure.”

How does this change medicine?

The medical textbook Gray’s Anatomy has since updated its text to include the new definition of the mesentery.

But what determines when a structure officially becomes an organ?

“That’s a fascinating question. I actually don’t know who the final arbiter of that is,” Coffey says.

Nonetheless, Coffey and his team believe that the findings have provided a platform that can help direct future scientific and medical research involving the mesentery’s role in physiology, health and disease, which could ultimately lead to development of new treatments.

“Now we have established anatomy and the structure. The next step is the function. If you understand the function you can identify abnormal function, and then you have disease.” he added.

“Put them all together and you have the field of mesenteric science.”

Yet, if the physiological function of the mesentery has never been known, why is it important to unveil it now?

“Without it you can’t live,” Coffey said, adding that the mesentery is integrated with the intestine in an area that has yet to be fully studied.

“There are no reported instances of a Homo sapien living without a mesentery.”

An example he cited was that the structure of the mesentery in apes and other animals that walk on all fours were slightly different than that in the human body.

By understanding the anatomical arrangement of the abdominal organs and digestive system, certain diseases such as Crohn’s disease or irritable bowel syndrome may finally be unravelled.

“There are a lot of diseases that we are stalled on, and we need to refresh our approach to these diseases,” Coffey added. “Now that we’ve clarified its structure, we can systematically examine it. We’re at a very exciting place right now.” MIMS

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