Body's best kept secrets: Discovery of new organ could change medicine

How well do you know your body? For centuries, the human body has been mapped out and studied in great detail, yet researchers continue to make surprising discoveries. In recent years, scientists have identified and reclassified certain structures as organs, deepening our understanding of human anatomy and disease. Two of the most notable findings include the mesentery, recognised as an organ in 2016, and the interstitium, identified as a potential organ in 2018.

These discoveries could significantly impact medical research and treatment.

The mesentery is a double fold of the peritoneum—the lining of the abdominal cavity—that connects the intestine to the abdomen. It had long been considered a fragmented series of structures rather than a continuous organ. However, in 2016, researchers led by Professor J. Calvin Coffey at the University Hospital Limerick in Ireland demonstrated that the mesentery is a single, unified organ. Their findings, published in The Lancet Gastroenterology and Hepatology, provided the anatomical and structural basis to classify it as such. “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,” said Professor Coffey.

Medical textbooks, including Gray’s Anatomy, have since been updated to reflect this change, officially recognising the mesentery as the 79th organ in the human body.

Despite its classification, the exact function of the mesentery remains unclear. Scientists suspect it plays a crucial role in supporting and nourishing the digestive organs, as well as contributing to immune responses and fat storage.

By studying the mesentery as an organ, researchers hope to gain insights into conditions, such as colorectal cancer, inflammatory bowel disease, diabetes, and obesity. Professor Coffey believes this discovery opens the door to an entirely new field of medical research, which he calls mesenteric science.

In 2018, another remarkable discovery emerged. A group of scientists identified what they believe could be one of the largest organs in the human body—the interstitium.

This vast network of fluid-filled compartments, found throughout the body, had remained unnoticed for decades due to the limitations of traditional microscopic techniques.

The interstitium consists of dense connective tissues and fluid-filled spaces located beneath the skin and around organs, muscles, and blood vessels. Previously, it had been thought to be merely compact connective tissue, but new imaging technology revealed its true structure.

Scientists had failed to recognise the interstitium before because conventional histological techniques, which involve slicing tissue into thin sections and treating them with chemicals, drained away the fluid. This caused the tissue to collapse, giving it the appearance of a solid structure under a microscope. The discovery was made when endoscopists used new laser technology that allowed them to view living tissues in real time. What they saw were interconnecting fluid-filled compartments that did not match any previously known anatomical structures.

The interstitium, scientists believe may act as a shock absorber, protecting tissues from damage caused by movement. It may play a role in the spread of cancer and other diseases.

Interstitial fluid is a key component of lymph, which carries white blood cells to different parts of the body, making it an essential part of the immune system. Understanding this system better could lead to breakthroughs in cancer diagnosis and treatment.