What Is the Mesothelium?

The mesothelium was formerly believed to solely serve as a slippery, protective coating for certain organs. But, the mesothelium does more than help to separate and protect organs from rubbing against each other.

It also helps regulate response to injury, infection and disease. Research has revealed a number of functions such as transporting fluid and controlling inflammation.

The mesothelium goes by different names depending upon the parts of the body it covers.

• The pleura covers the lungs and chest wall
• The peritoneum covers the abdominal organs and abdominal wall
• The pericardium covers the heart
• The tunica vaginalis covers the testes

Asbestos exposure can damage the mesothelium. How asbestos fibers reach the mesothelium is not quite understood. Researchers have proposed the lymphatic system may transport asbestos fibers to the mesothelium.

Exposure to asbestos can cause mesothelioma and other asbestos-related diseases in the mesothelium.

Mesothelium Structure and Function

The mesothelium is made up of two layers:

• The visceral layer covers the organ
• The parietal layer covers the body cavity

These layers are composed of mesothelial cells, which are flattened squamous-like epithelial cells.

Quick Fact:

The mesothelium is a slowly renewing tissue. Less than 1 percent of the cells undergo cell division at any one time.

The primary function of the mesothelium is to provide a protective surface. This surface is flexible and not restrictive of the organs it covers.

Other functions of the mesothelium include:

• Transporting fluids and cells
• Inflammation and tissue repair
• Protection against invading microorganisms
• Presenting antigens (immune proteins) to lymphocytes (immune cells)
• Blood clotting to heal wounds
• Tumor cell adhesion to prevent cancerous spreading

Diseases of the Mesothelium

Inflammation, scarring and cancer can develop in the mesothelium. Improper healing of damage to the mesothelium can cause fibrous adhesions to develop. Cancerous changes to mesothelial cells leads to malignant mesothelioma and other cancers.

Effusions, or the accumulation of fluid between the layers of the mesothelium, can develop as a result of inflammation and cancer in the mesothelium. Effusions are considered a symptom of mesothelial diseases, not a primary disease.

• Pleural effusion accumulates around the lungs.
• Peritoneal effusion accumulates around the abdomen.

Pleural Diseases

Benign and cancerous diseases of the pleura can develop as a result of asbestos exposure.

• Pleuritis is inflammation of the pleura.
• Pleural plaques are fibrous scar tissue on the pleura that may become calcified.
• Pleural thickening is extensive scarring that thickens and restricts the pleura.
• Atelectasis is a contraction of pleural scar tissue that folds the pleura into the lung. This causes the lungs to underinflate.
• Pleural mesothelioma is cancer of the pleura.

Peritoneal Diseases

Benign and cancerous diseases can also develop in the peritoneum.

• Peritonitis is inflammation of the peritoneum.
• Peritoneal mesothelioma is cancer of the peritoneum.
• Primary peritoneal serous carcinoma is another cancer of the peritoneum.

Peritonitis is most often caused by a bacterial or fungal infection. Peritoneal mesothelioma is largely caused by asbestos exposure. The causes of primary peritoneal serous carcinoma are unknown.

Pericardial Diseases

Several benign conditions and cancers can develop in the pericardium.

• Pericarditis is inflammation of the pericardium.
• Cardiac tamponade is compression of the heart by fluid accumulation.
• Pericardial constriction is scarring and a loss of elasticity of the pericardium.
• Pericardial mesothelioma is cancer of the pericardium.
• Several other cancers can develop in the pericardium, including sarcomas, lymphoma and primitive neuroectodermal tumor.

Tunica Vaginalis Diseases

Benign and cancerous diseases can develop in the tunica vaginalis.

• Hydrocele is an abnormal amount of fluid between the layers of the tunica vaginalis.
• Scrotal calculi are calcified deposits that form between the layers of the tunica vaginalis.
• Fibrous pseudotumors are benign lesions of the tunica vaginalis.
• Testicular mesothelioma is cancer of the tunica vaginalis.
• Several other cancers can develop in the tunica vaginalis including mesenchymal tumors, lymphomas and serous borderline tumors.
• A few benign tumors can develop as well, including adenomatoid tumor, scrotal tunica cyst, lipoma and leiomyoma.

The mesothelium plays an important role in protecting organs and responding to inflammation, injury and disease.

Make an appointment with your doctor if you have a history of asbestos exposure and develop abnormal symptoms affecting the lungs, abdomen, heart or testes.