Meet Your Newest Organ: The Mesentery

Scientists are calling for an upgrade in classification of this vital gut membrane

J. Calvin Coffey holds up a model of the mesentery Alan Place/University of Limerick

There are 78 different organs in the human body—but there may actually be 79, reports Tom Embury-Dennis at The Independent. That’s because researchers at University Hospital in Limerick, Ireland, are calling for a recategorization of the mesentery—a structure found in the intestines—as a full-fledged organ.

According to Ben Guarino at The Washington Post, the mesentery has been in the anatomy books for over a century. In fact, Leonardo da Vinci even described it in 1508. But doctors believed the two-walled sheet of membrane, which lines the abdominal cavity, was a disjointed series of tissues spread throughout the area and not connected together.

It wasn’t until J. Calvin Coffey, a surgeon at the University of Limerick, began looking more closely at the mesentery that he found it was in fact one continuous ribbon of tissue, documented in several studies in 2012 and 2014. Coffey has continued his work examining the mesentery more closely, coming to the conclusion that it is indeed an organ, laying out his reasons in a recent edition of the medical journal The Lancet.

“The anatomic description that had been laid down over 100 years of anatomy was incorrect. This organ is far from fragmented and complex,” Coffey says in a press release. “It is simply one continuous structure. We are now saying we have an organ in the body which hasn’t been acknowledged as such to date.”​

The well-known medical text Gray’s Anatomy added the structure to its latest 2015 revision, reports Embury-Dennis. Even so, it remains unclear who officially defines an organ. ​​"I actually don’t know who the final arbiter of that is,” Coffey tells Nathaniel Scharping at Discover.

There is also one big problem with defining the organ: no one knows exactly what the mesentery's function is. That’s something Coffey hopes to investigate. He also hopes to determine whether it has a distinctive cell type. What he does know is that it is important. “Without it you can’t live,” Coffey tells Scharping. “There are no reported instances of a Homo sapien living without a mesentery.”

Classifying the mesentery as an organ is not just a matter of semantics either. In the press release, Coffey says treating the mesentery like an organ could lead to medical breakthroughs. By studying and understanding the function of the organ, researchers could begin to understand dysfunction and diseases caused by problems with the mesentery.

Scharping reports that it could help in figuring out hard to understand diseases of the gut like Crohn’s disease and irritable bowel syndrome. “There are a lot of disease that we are stalled on, and we need to refresh our approach to these diseases,” Coffey tells him. “Now that we’ve clarified its structure, we can systematically examine it. We’re at a very exciting place right now.”

Get the latest stories in your inbox every weekday.