Mesothelium

Summary of the characteristics of the mesothelium, a membrane distributed throughout various parts of the body.

Researchers, with current knowledge, have been able to calculate that the human body houses about 30 trillion cells. Undoubtedly, each tissue has its particularities, and, for example, 84% of this cell volume in our species corresponds to red blood cells, which carry oxygen in the blood. Yes, as strange as it may sound, many experts regard blood as a type of connective tissue that is fluid in nature.

Human beings are 50% proteins since they make up half of our dry tissue, and, as you can imagine, the biological system that makes us up cannot be conceived without tissue as a basic level of organization beyond the cell. It’s all about perspective, but, in short, without tissue organization, we are nothing.

All this introduction comes to underline the diversity and importance of tissues in our body. We all know what nervous or muscular tissue is due to its clear functionality, but what comes to mind if we name you the term “mesothelium”? If the answer is nothing, don’t worry, because here we tell you everything you need to know about it.

What is the mesothelium?

We started directly. From a physiological point of view, the mesothelium is defined as a type of simple squamous epithelium that rests on a basal lamina supported by connective tissue. We dissect each of these terms:

  • Epithelium: a tissue made up of closely-knit cells (flat or prismatic), which lines the body’s external surface and certain organs.
  • Simple epithelium: deepening one more category, the simple epithelium is constituted by a single layer of cells in contact through union complexes.
  • Squamous (stratified) epithelium: composed of a layer of flattened (squamous) cells on a basement membrane.

That makes it clearer, right? We are talking about a really simple type of tissue: a single layer of cells in a flattened shape. To locate this curious tissue, we must emphasize that it is the peritoneum’s outermost layer, but what is this?

The peritoneum is the serous layer that lines the interior of the abdominal cavity, that is, the “hollow space” in which all our organs are housed. This is composed of two layers and, between them, there is a space (peritoneal cavity) that contains about 50 milliliters of lubricating fluid that allows them to slide together.

It is the most extensive serous membrane in the body because it also shelters our intestines in addition to lining the peritoneal cavity. It is estimated that, for this reason, it occupies 40-50% of the total skin surface.

The mesothelial cell

We have already described the general shape of the mesothelium and its location, which is why we can only pay special attention to its basic functional unit, the mesothelial cell, to complete the panorama of this unique tissue. Go for it.

The mesothelial cell is of a flat epithelial type, of mesenchymal origin (loose conjunctiva of embryonic origin) that lines the serous cavities. These cells form a monolayer with a polygonal mosaic appearance in which certain microvilli emerge.

The proteins and serous fluids that are trapped between these microvilli provide a low friction surface, which provides an excellent area of ​​contact between organs. On the other hand, these cells rest on a basement membrane (MB) that offers little resistance to the passage of molecules of less than 30,000 daltons.

Finally, it should be noted that mesothelial cells are very reactive. This means that they change their appearance easily. For example, they are observed in well-organized groups of different volumes when they are at rest, with a high nucleus: cytoplasm ratio.

On the other hand, as they are activated, they increase in size, forming irregular cytoplasmic protrusions and greater vacuolization. Unfortunately, this plasticity can be a problem: we have to talk about cancer in future lines.

Mesothelium functions

The main purpose of the mesothelial cells (and therefore the mesothelium) is to create a layer of lubricating fluid that is released between layers of coating, producing a slippery, non-sticky surface.

In addition to this, the mesothelium also supposes the transport and movement of particles and cells between cavities, among which are the leukocytes, involved in the immune response as inflammatory mediators. In short, it is a “passing” tissue that allows the gliding between organs and the transport of various substances and cell bodies essential for the physiological well-being of the body.

Like virtually all cells in the body that grow and change, the mesothelium is a potential candidate for cancer events. After all, cancer is nothing more than a mutation in a cell that causes it to divide uncontrollably and does not respond to normal periods of apoptosis (cell death), giving rise to the dreaded malignant tumor.

Mesothelioma, cancer in the mesothelium

Mesothelioma can be divided into various categories depending on where it is affected. Among them, we find the following.

  1. Pleural mesothelioma

It affects the tissue that surrounds the lungs; that is, it develops in the thoracic cavity. It can cause chest pain, painful cough, shortness of breath, unusual lumps under the skin of the chest, and unexplained weight loss, among many other things.

  1. Peritoneal mesothelioma

As its name suggests, it affects the tissue of the abdomen (peritoneum). It causes bloating, abdominal pain, nausea, and weight loss for no apparent reason. Unfortunately, both types of mesothelioma are extremely aggressive and carry a non-negligible fatality rate.

  1. Other types of mesothelioma

There are more types of mesothelioma depending on the tissue they affect because, for example, pericardial mesothelioma grows in the tissue around the heart, causing respiratory problems and tightness.

On the other hand, tunica vaginalis mesothelioma affects the lining of the testicles. Basically, any mesothelial lining is susceptible to the development of a malignant tumor, although not all mesothelial tumors automatically translate into cancer.

Distribution and epidemiology of mesotheliomas

Mesothelioma appears in approximately 1-2 patients per million people per year. Unfortunately, people who work in the construction sector (especially if they are in contact with asbestos) are up to 40 times more likely to present it.

This aggressive type of cancer kills about 5,000 people a year in Europe and 3,000 in the US a year.

A typical mesothelioma patient is a 60-year-old man who has been working in this type of industry for at least 30 years. It is shocking to learn that, in most cases, it usually takes 20 to 40 years after exposure to asbestos (in vinyl, cars, and building materials) until cancer develops.

For this reason, the World Health Organization (WHO) has recommended that all countries in the world stop using this material in construction. Unfortunately, in 2010 this organization estimated that, despite global bans, 125 million people around the globe are still in close contact with asbestos. 

In addition to mesothelioma, this material also causes asbestosis (scar lesions in the lung and pleura) and lung cancer, as well as possible metastases derived from these types of malignant tumors.

Summary

As you have seen, the mesothelium is a very simple structure that has many secrets to unravel. To understand each other (and in a more familiar final point), we can say that it is a simple layer that allows the sliding between organs and the transport of substances, from proteins to specialized immune bodies, passing through many other cell types.

Mesotheliomas are a very rare type of malignant tumor in the general population, but, unfortunately, they occur almost exclusively in people who have worked on works in contact with asbestos.

If you have a hard work / physical work history and notice strange lumps in any soft part of your body, abdominal swelling, and continuous coughing, see a doctor quickly.

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