Scientists Discover a New Human Organ Called the 'Interstitium'

The interstitium was simply thought to be dense connective tissue that enclosed fluid-filled spaces.

Co-senior author, Dr. Neil Theise, a pathologist at NYU Langone Health in NY, points out that the interstitium may actually be the largest organ in the human body.

The paper defines the newly discovered organ as a "fluid-filled space within and between tissues" that spreads throughout the body and can be found almost everywhere: under the skin, between our organs, around arteries and veins, along the fibrous tissue between muscles, and even around the digestive tract and urinary system. "The presence of fluid has important implications for tissue function and pathology", the team adds.

Schematic of the fluid-filled space supported by a network of collagen bundles lined on one side with cells.

But, when the team made slides of the tissue, the pattern disappeared.

The team says their findings mean that that numerous normal and abnormal activities of different organs need to be reconsidered to include the newly discovered role that the nearby interstitium appears to play.

Researchers have known about the presence of interstitial tissue - connective tissue and fluid between organs in the body - for a long time.

They took pictures, which were shown to Neil Theisse, the author of the paper and a professor at NYU's School of Medicine, who theorizes that the interstitium's goal may have to do with the immune system, as it moves through the lymphatic system.

Theise says that this is found in interstitium, which totals about "10 litres of fluid" inside the human body.

More research is likely to be needed to find out whether this improved understanding of the interstitium can be used to fight disease.

This series of spaces, supported by a meshwork of strong (collagen) and flexible (elastin) connective tissue proteins, may act like shock absorbers that keep tissues from tearing as organs, muscles, and vessels squeeze, pump, and pulse as part of daily function.

The authors-led by gastroenterologist David Carr-Locke of Weill Cornell Medicine and pathologist Neil Theise of NYU Langone Health-lay out an explanation as to why this cushioning tissue has been missed in the past. When the tissue samples were removed from the body, they were quickly frozen, which allowed the fluid-filled spaces to stay open so the researchers could see them under a microscope.

Theise and his colleagues made use of a power microscope and a technique called confocal laser endomicroscopy to closely examine healthy living tissue samples taken from human bile ducts. She cautions that the findings are limited to a fairly small number of patients and that most of the tissues the authors looked at outside of the bile duct were fixed, not live or freshly frozen. Although the new organ has the crucial role of cushioning internal organs, it seems it can also carry cancer cells from tumors into the lymphatic system causing cancer to spread through the body.

In addition to protecting organs, scientists suspect the network may also assist in the spread of cancer cells.

This is not the first new organ to be discovered in recent years.

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