The Human Body has a New Organ

By Rachel Washburn

The news during the week of January 3rd, 2017 was filled with headlines of: A brand-new human organ has been classified¹, The human body’s 79^th organ², Meet your newest organ³, A new organ you didn’t know you had⁴, and Scientists discover a new organ in the human body⁵. It’s not every day that the human body gets a new organ. I am fascinated with the field of anatomy and physiology so I read all these articles, and continued on to read the paper⁶ behind it all: The mesentery: structure, function, and role in disease by Coffey and O’Leary.  So, what is the mesentery?

Located in the human abdominal cavity with the digestive organs are layers of tissue called the mesentery. Until recently, the mesentery has remained a relatively ignored part of human anatomy.  Research through 1879 from Leonardo Da Vinci’s drawings to surgical sketches to the Austrian anatomist Carl Toldt’s findings of mesenteric-digestive system structure supported the idea that the mesentery is continuous tissue. Yet, the research of surgeon Sir Fredrick Treves has been the preferred hypothesis through today, stating that the mesentery is a fragmented structure only found in some parts of the digestive tract. In fact, my 2015 human anatomy text book⁷ describes the mesentery as disjointed double-sheeted peritoneal membranes attached to some specific parts of the intestines. This prominent hypothesis, which has been around since 1885, has been refuted by current research. New findings now support the idea of a continuous mesentery, and a new hypothesis: the mesentery is an organ.

Figure 1: Diagram of mesentery structure

The Lancet Gastroenterology & Hepatology 2016 1, 238-247DOI: (10.1016/S2468-1253(16)30026-7

The mesentery is discovered to be continuous only when thorough investigation through dissection was applied. Contiguity was further confirmed with analyses from the Visible Human Project data sets, which is a database that contains anatomically correct and detailed images of human male and female normal anatomy. The disconnected mesentery hypothesis didn’t fit with surgical reference texts, and radiological anatomical maps have determined its continuous structure. Now radiologists can ascertain true mesenteric abnormalities instead of viewing normal mesenteric structure as an abnormality. Overlap of intestinal connective tissue and mesenteric connective tissue was found to be the interface between the intestine and the body environment. The mesentery was found to be innervated by the parasympathetic and enteric nervous systems, but further research is needed in this area to determine the extent of the innervation and how this affects the organ’s function.

With the reclassification of the mesentery as an organ, more well-defined surgical nomenclature can be developed to better standardize and notate surgery, to provide clearer comparisons of surgeries, and to clarify anatomical and surgical instruction. The new map of the mesentery’s flexural anatomy simplifies colorectal surgical specifications and aspects, with newly proposed labeling of the now-continuous fascia and tissues. Parts of mesenteric tissue were labeled as these fascia, but have been found to be epithelial tissue making the mesentery the largest mesothelium in the body.

Figure 2: Relationship of mesentery, intestines/colon, fascia, and peritoneum

The Lancet Gastroenterology & Hepatology 2016 1, 238-247DOI: (10.1016/S2468-1253(16)30026-7)

Furthermore, this reclassification brings with it a new field of study: mesenteric science. Mesenteric science will standardize and consolidate research done on the mesentery, which has previously been completed under many unrelated topics. Additionally, this new field of study will have more focus, more funding, and more insight into health, disease, and autoimmunity than ever before completed on the mesentery.

The discovery of the continuous structure of the mesentery sheds light on more of its functions. As known before, the mesentery suspends and keeps the intestines in place during movement to prevent intestinal torsion or collapsing. The mesentery also keeps intestinal transit operational and suspends the colon to maintain its shape and proper function. New research on mesenteric structure now supports that the mesentery samples intestinal environment to deliver an immune response if necessary. The mesentery also produces C-reactive protein, which regulates fat and carbohydrate metabolism and may also contribute to inflammatory and coagulation regulation. 

Better understanding of the mesentery structure allows scientist and medical doctors to better understand mesenteric function. In turn, abnormalities can be identified and used to find relationships to diseases. With the new map of continuous mesentery structure, doctors have found that intestinal torsion and hernias could be caused by incomplete fetal development of the mesentery. Fatalities from abdominal crisis are now associated with malrotation of the mesentery during embryological development. The discovery that the mesentery and the small intestines are attached by lymphatics unveiled an avenue of how intestinal tumors can spread. Mesenchymal cells responsible for Crohn’s disease extend from the mesentery into other intestinal areas and are typical in the adipose wrapping of the mesentery. The mesentery has been found to contribute greatly to visceral fat and may have ties in obesity, diabetes, autoimmunity, and metabolic diseases. Identifying these abnormalities allow researchers to find better avenues of treatment.

I struggle with an autoimmune disease, and upon reading this paper, I was fascinated by the implications reclassifying the mesentery as an organ will hold. Already, research is ensuing on how the mesentery interacts with the immune system and how that interaction could have an effect on autoimmune disease. I have many friends diagnosed with Crohn’s and Celiac’s disease, and with the discovery of Crohn’s mesenchymal cells in the mesentery, there is more resolved hope for better surgical options and treatment for them.

There is still much to be studied on the mesentery as an organ. The mesentery plays a role in the digestive, cardiovascular, endocrine, and immune systems; so the organ system in which to classify the mesentery is yet to be determined. Research is also needed to find and analyze the functional cell unit of the mesentery. The mesentery needs to be further researched with the same focus other human organs are under, and by so doing should improve diagnostic techniques, pathological treatments, and standardization of surgical procedures.

References

1         MacDonald, F. (2017). A brand new human organ has been classified. Science Alert. Retrieved from https://www.sciencealert.com/it-s-official-a-brand-new-human-organ-has-been-classified.

2         Scharping, N. (2017). The Human Body’s 79^th Organ. Discover Magazine. Retrieved from http://blogs.discovermagazine.com/d-brief/2017/01/03/the-mesentery-organ-human/#.Wa3OVMYVjIU

3         Daley, J. (2017). Meet Your Newest Organ. Smithsonian Magazine. Retrieved from http://www.smithsonianmag.com/smart-news/theres-new-organ-human-body-180961658/

4         Strickland, A. (2017). A new organ you didn’t know you had. CNN. Retrieved from http://www.cnn.com/2017/01/04/health/new-organ-mesentery/index.html4

5         Gajanan, M. (2017). Scientists discover new organ in human body. Time Magazine. Retrieved from http://time.com/4621074/mesentery-organ-human-body/

6         Coffey, C., & O’Leary, P. (2016). The mesentery: structure, function, and role in disease. The Lancet Gastroenterology and Hepatology. Retrieved from http://www.thelancet.com/journals/langas/article/PIIS2468-1253(16)30026-7/abstract

7         Martini, F., Nath, J., & Bartholomew, E. (2015). Fundamentals of Anatomy and Physiology Tenth Edition. Glenview, IL: Pearson.