The mesothelium is a little-known but important structure found in various areas of the body. Made of two layers, mesothelial structures cover and protect almost every internal organ, including the heart, lungs, and stomach. They are made of mesothelial cells, which are vulnerable to mutation. When mesothelial cells are exposed to the carcinogenic mineral asbestos, the result is often malignant mesothelioma.
What Is The Mesothelium and What Does It Do?
Mesothelial structures cover and protect our internal organs. They have inner layers that wrap around the organs and that are enveloped by outer layers with a small amount of fluid resting between the two. The mesothelium generally allows the body’s organs to move easily.
Different Structures of the Mesothelium
Although mesothelial structures have the same basic anatomy wherever they are located, they have been assigned different names based on what organ is being protected. The mesothelium that surrounds the lungs is called the pleura, with its inner layer called the visceral pleura and the outer layer called the parietal pleura.
The mesothelium that surrounds the abdominal organs is called the peritoneum, with its inner layer called the visceral peritoneum and its outer layer called the parietal peritoneum. There is also a mesothelium associated with the pericardial cavity and housing the heart, and a mesothelium surrounding the male and female reproductive organs called the tunica vaginalis.[1]
The Mesothelium’s Functions
It was originally believed that the mesothelium’s purpose was to enable movement of the organs against each other, preventing them from sticking to one another and the internal walls of the body. In recent years, it’s become apparent that it plays a role in allowing the lungs to expand during breathing, allowing the heart to expand and contract as it fills with blood and beats, and the intestines to expand and contract as they move their contents through the digestive system.
The fluids that the mesothelium emits, which have long been known to protect tissues from abrasion, are also now known to fight infection, and possibly the spread of tumors. They are pivotal to the development of the organs that they surround and to the transport and movement of fluid and particulate matter across the serosal cavities. They are essential to leucocyte migration in response to inflammation, and they synthesize pro-inflammatory cytokines, growth factors, and extracellular matrix proteins to assist with cell repair.[2]
Diseases of the Mesothelium
The mesothelium is vulnerable to several different pathological conditions. Most manifest with increased amounts of fluid between the inner and outer layer of the structure in response to inflammation of either the lining itself or the organs that they surround. Pleural effusions within the mesothelium surrounding the lungs can reach increased volumes of up to 1.5 liters, causing significant pain and diminished lung function.
Conditions that can cause inflammation of the mesothelium include:
- Infectious diseases such as tuberculosis
- Dressler syndrome, a form of pericarditis resulting from an immune response after damage to heart tissue
- Viral infections such as HIV
- Cancer and inflammatory diseases, especially autoimmune disorders such as systemic lupus erythematosus
- Kidney failure with uremia
- Tumors that have metastasized from distant sites
Inflammation of the mesothelium can also be caused by:
- Radiation therapy
- Chemotherapy
- Some medications
The Mesothelium and Mesothelioma
The mesothelium is vulnerable to primary tumors that can form in the pleural, pericardial, peritoneal, and tunica vaginalis cavities. Known as malignant mesothelioma, these cancers are caused by exposure to asbestos fibers that become trapped in the mesothelial cells. Though there are several different mechanisms at play leading to the development of malignant mesothelioma, it is generally true that DNA damage caused by these carcinogenic fibers leads to inflammation, mutation, and proliferation into tumors.
Though mesothelioma can form in any of the mesothelial structures, 70 to 80% manifest in the pleural cavity, leading to malignant pleural mesothelioma. The other 20% form in the peritoneum, with very few cases of pericardial or tunica mesothelioma. Mesothelioma has a median latency period of approximately 39 years and has an extremely poor prognosis.
Symptoms of Mesothelioma
Malignant mesothelioma manifests in each region of the body in different ways.
Malignant pleural mesothelioma’s symptoms include:
- Chest pain
- Coughing
- Coughing up blood
- Difficulty swallowing
- Fatigue and muscle weakness
- Night sweats and fever
- Shortness of breath
- Weight loss
- Wheezing
Symptoms of malignant peritoneal mesothelioma include:
- Abdominal pain
- Buildup of fluids
- Decreased appetite and weight loss
- Gastrointestinal symptoms
- Fatigue
Symptoms of malignant pericardial mesothelioma include:
- Trouble breathing
- Shortness of breath
- Chest pain
- Fatigue and fever
- Heart murmurs
Symptoms of testicular mesothelioma include:
- A buildup of fluid between the layers of the mesothelium within the scrotum
- A lump under the skin on one or both of the testicles
If you have a history of exposure to asbestos and experience any of these symptoms, it is essential that you consult with a physician as soon as possible, making sure that you inform your doctor of the details of your exposure.
