MESENTERE: anatomy, functions, pathologies

Mesentery

What is the mesentery?

If you had asked us this question a little over a year ago, we would have answered you: it is one fold of the peritoneum, in which blood vessels, lymphatic vessels and nerves flow, which anchors the small intestine (or small intestine) to the posterior wall of the abdomen, allowing peristaltic movements in a relatively free way and ensuring the supply of nutrients and oxygen. Today, however, in the light of recent discoveries in this regard we answer you in a different way: the Mesentere is a organ of the human body. But what is an organ? IS' an anatomical unit capable of performing specific functions. Therefore today the Mesentere is no longer "part of something else", but is itself a functioning unit, able to guarantee the fulfillment of specific tasks. In an article published in the November 2017 issue of one of the leading medical journals, "The Lancet - Gastroenterology & Hepatology", Professor Coffey, Irish, defined the criteria that delineate the mesentery as an organ from continuous structure, and no longer as an accessory and disorganized fabric. Therefore, it will have to be considered in the future on a par with all the other organs, starting from the diagnosis phase and ending with the therapeutic phase, with particular research possibilities.

Anatomy and structure of the Mesentery

What, then, are its functions? To say this, as always in medicine, it is necessary to first investigate its structure, both microscopic and macroscopic; in fact it is always the form that adapts to the function, and it is precisely from the study of the morphology of the Mesentere that it has been reclassified as an Organ. So let's go and discover it.

Here are some key concepts:

  • The mesentery is an extension of the large sac that surrounds the internal wall of the abdomen, the peritoneum.
  • Its origin from the peritoneum draws an oblique line on the posterior wall of the abdomen, which is called the root of the mesentery.
  • It is made up of two layers (called sheets) made of the same tissue as the peritoneum from which they originate (peritoneal mesothelium), between which blood vessels, lymphatic vessels, nerves and connective tissue flow.
  • We can therefore imagine the sheets as two slices of bread, and the vessels, the nerves and the connective tissue as the filling. In the "filling" the lymph nodes are abundant, that is the "immunological customs" that control everything that comes from the intestinal lumen.
  • From the posterior abdominal wall the mesentery moves forward and reaches the loops of the Small Intestine, which are wrapped by the two sheets, which anchor them in this way to the wall.
  • With an open abdomen, it has folds that make it assume a fan shape, and has a yellowish color, in which the blood vessels are visible in the form of very thin and dense red-blue strips.

At the macroscopic level, it appears as a fold originating from the posterior wall of theabdomen, obliquely from top to bottom and from left to right. In particular, the root of the mesentery (thus the parietal origin of this organ is identified) originates in the upper left at the level of the duodenal-jejunal flexure (i.e. a sort of kneeling of the fourth portion of the Duodenum, which is carried forward by bending downwards, from which the Jejunum, second portion of the Small Intestine) and ends in the lower right at the level of the right sacroiliac joint (therefore, where the vertebral column articulates with the pelvis).

We have therefore seen from where is it originates the mesentery. But such asinstead, does it arise from the Peritoneum? We must imagine that at the root level, this thin serous sheet which is the parietal peritoneum opens in two, leaving a small slit in the middle; the two portions into which it divides then slide one over the other heading towards the intestinal loops, welcoming together the aforementioned vascular and nervous structures, which insinuate themselves between the two sheets at the level of the crack left on the wall. And here the mesentery is therefore formed by two sheets, one right looking up, and one left looking down, which, like the slices of bread in a sandwich, accommodate structures that are led to the intestinal loops. In fact, it is precisely here that the two sheets end, wrapping the intestinal wall.

Mesentery and intra-abdominal organs

Abdominal organs connected via the mesentery.

How long is the road that divides the starting point from the arrival point? Very little at the extremities, therefore at the level of the duodenal-jejunal flexure and the ileocecal valve (which represent respectively the first and last intestinal portion reached by the mesentery), while much more as one proceeds towards the center; therefore it is easy to understand how the extremities are the regions where the least degree of movement is allowed, and vice versa for the median loops: as for a dog on a leash, the longer it is, the more the dog will be free to move and to cover a greater angle of movement, and vice versa. Since the root, on the abdominal wall, is between 10 and 20 centimeters long, while the intestine is known to be a few meters long, up to 7, inevitably the mesentery will have to be folded several times to be able to accommodate such a long structure distally, assuming a shape that is very reminiscent of that of a partially open fan.

We have thus described the Mesentery in a macroscopic way. But if we got closer and closer, observing it first with the naked eye, as a surgeon could do during an abdominal operation, and then with the aid of microscopes, as a pathologist could do, what would we see? First of all, at first glance, we would notice the dense vascular network that runs through it: under the thin translucent sheet, arterial and venous vessels would peek out to cover the whole area. But not only: with the aid of palpation, it would be possible to ascertain the presence of small structures with a vaguely oval shape, similar to lentils; are the lymph nodes, of which the gastro-enteric system is richly supplied, and among which the Mesentery is certainly no exception. The abundance of lymph nodes means one thing above all: there is a strong presence of immune cells in the mesentery, therefore an important control of everything that transits or stays inside the intestine. In fact, the lymph nodes behave like control stations placed along the path of the lymphatic vessels: they check that there is nothing foreign, of “non-self”, and if not, they trigger the reactions aimed at eliminating it.

But we know how complex the immune response is, rich in regulations and counter-regulations, governed by mechanisms that are often still hidden or unclear from us. Just think of auto-immunity, the process by which our immune system attacks structures of our organism as if they were foreign: often, why, how, when and on the basis of what environmental and genetic stimuli, this phenomenon does not occur. it is still clear; this is of particular importance in the context of enteric pathology, in which a sadly known role is played by a pathology of an autoimmune nature but still with an unfavorable prognosis and with many aspects to be clarified, Crohn's disease. Therefore, the Mesentery and all its immune system certainly represent at the same time a source of defense but also an unknown factor and a possible source of new pathophysiological and therapeutic discoveries regarding some diseases, intestinal and otherwise.

Functions of the Mesentery

Describing the structure of the mesentery, we have already mentioned or at least suggested many of the functions of the mesentery, waiting for others, now only hypothesized, to be ascertained with the passage of time by scientific research, hopefully revolutionizing the world of gastro-enterology and not. only. So let's list them:

  • Mechanical function: anchor of the intestinal loops to the posterior abdominal wall, ensuring not only anatomical stability (avoiding for example the fearful intestinal torsion) but also at the same time the possibility of movement.
  • Function of immunological surveillance: monitoring of the intestinal environment, with the triggering of immune responses, acute or chronic, local or systemic, in response to the presence of bacteria (we take this opportunity to remember the enormous importance that normal intestinal bacterial flora assumes in the maintenance of homeostasis, or equilibrium, of the entire organism: it is possible that an alteration of the flora leads to alterations in distant organs precisely through the triggering of immune processes at the level of the peri-intestinal lymph nodes, such as those mesenteric).
  • It regulates inflammation and the blood coagulation process (observation made exclusively on animal models and therefore the subject of research especially as regards the possible favorable implications in the field of abdominal surgery).

Diseases of the Mesentery:

Net of what was previously discussed regarding the possible implications in enteric and non-enteric pathologies, the Mesentery to date essentially recognizes neoplastic and inflammatory as primary pathology (that is, it primarily affects this same organ, and not others).

  • Benign tumors: fortunately they are more frequent, and are mainly fibroids and lipomas (remember: the suffix -oma indicates the benignity of the lesion, while the prefix indicates the tissue origin of the lesion: in this case, therefore, fibroid will indicate a neoplasm benign of connective fibrous tissue, while lipoma is a benign neoplasm of adipose tissue). They appear as masses that can also be of considerable size before giving symptoms, and which therefore are often randomly diagnosed during investigations for other reasons. Sometimes, however, they reach such dimensions as to cause symptoms, such as vague pain or meteorism (in fact, the mass can compress the intestine, causing a stagnation of material upstream of the stenosis, which being fermented by the bacteria of the flora produces gas and therefore meteorism) .
  • Malignant tumors: are mainly represented by mesothelioma is leiomyosarcoma (leiomio- indicates the origin from the smooth muscle, while -sarcoma stands for malignant neoplasm of the connective tissue; Mesothelioma instead indicates the malignant neoplasm originating from the mesothelium of the serous membranes, in this case the peritoneum). The symptoms are the non-specific ones of the neoplasms (weight loss, repeated fatigue, anorexia ...), and in some cases the presence of ascites, sometimes chylous (i.e. the free liquid in the abdominal cavity is made up of lymph, of a color and consistency very similar to the milk, which oozes from lymphatic vessels blocked by the tumor).
  • Mesenteric lymphadenitis: inflammation of the mesenteric lymph nodes, usually secondary to intestinal infection. It expresses itself with abdominal pain and fever, and possibly symptoms due to the infection (diarrhea, vomiting ...). The inflammation ends with the effective treatment of the underlying infection.
  • Mesenteritis: acute or chronic inflammation of the mesentery, usually secondary to diseases of the digestive system (intestinal tuberculosis, Crohn's disease or other infectious or inflammatory diseases). It presents with diffuse fibrotic thickening of the mesenteric fan. A primary inflammation of the mesentery is the retractable mesenteritis, characterized by thickening and retraction of the mesenteric fan, with consequent disturbances of intestinal motility up to complete occlusion.

All of these pathologies can be diagnosed by means of abdominal CT or abdominal ultrasound. These diagnostic techniques are also crucial to prove a possible thickening of the mesentery, due to inflammation and frequently to the exudation of lymphatic fluid.

 

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