In one of my online biology classes last week, a student asked if I had any comments on the new organ that was just discovered in the human body. I didn’t have any comments, because I didn’t know anything about it. I expressed a lot of skepticism, saying that with all the imaging techniques available to scientists, it’s hard to imagine that an organ in the human body has been missed. However, I promised the student I would look into it, and while I hesitate to call it a new organ, it turns out that a new feature of the human body has most certainly been discovered!
You can read about it in the open-access article published by Scientific Reports. As shown in the illustration above, the researchers found that wherever tissues are stretched or compressed (like the lungs or even the intestines), there is a network of fluid-filled spaces underneath. In the illustration above, think of the part labeled “Mucosa” as the lining of an organ. Underneath that lining, there is a mesh of collagen proteins and elastin proteins (elastin is a part of the “collagen bundle” in the illustration). Those proteins have specific cells attached to them that react to CD34, a stain used to highlight a feature of certain cells when they are viewed under a microscope. In between this mesh of proteins and cells, the spaces are filled with fluid.
For a long time, anatomists have understood that there is a lot of fluid in between the cells of an organism. It is called “interstitial fluid,” and it makes up about 16% of the human body’s weight. It bathes the cells, keeping their environment reasonably constant and serving as way that cells can exchange chemicals with the rest of the body. It comes from the blood, and then it drains into the lymphatic system, where it is cleaned and returned to the blood. So the fluid found in those spaces is not new. The fact that the fluid is found in a mesh of proteins and cells and forms the sponge-like structure illustrated above was completely unknown up to this point.