A part of the digestive system has been reclassified as an organ, following research at the University of Limerick.
The mesentery, which connects the intestine to the stomach, was previously thought to be made up of lots of separate parts.
But Irish surgeon Prof J Calvin Coffey discovered it was one single structure.
He said his research, published in the Lancet Gastroenterology & Hepatology, could lead to a new area of science and better understanding of disease.
There are now 79 organs in the human body, and medical textbook Gray's Anatomy has been updated to include the mesentery.
But more scientific research is now needed to work out exactly what the organ does.
Prof Coffey said: "Now we have established anatomy and structure. The next step is function.
"If you understand the function you can identify abnormal function, then you have disease.
"Put them all together and you have the field of mesenteric science."
He said the mesentery should be now be investigated to the same degree as other organs and systems in the human body.
And it could have a role to play in diseases such as colorectal cancer, inflammatory bowel disease, diabetes and obesity.
The mesentery is a double fold of the peritoneum, the lining of the abdominal cavity, which attaches the stomach, small intestine, colon and other organs to the abdomen.
"When we approach it like every other organ, we can categorise abdominal disease in terms of this organ," Prof Coffey said.