The mesothelium is a thin, two-layer membrane that surrounds the entire surface of the lungs and heart as well as the organs in the abdomen. The mesothelial lining of the lungs is called the pleura, the lining of the heart is called the pericardium, and the lining of the abdomen is called the peritoneum.
The mesothelium protects your internal organs, and produces a lubricating fluid that allows your lungs and heart to glide easily against your chest wall. Without this protective lining, your lungs and heart would be unable to expand and contract freely. Thus, while few people have ever heard of the mesothelium, your body cannot function normally without it.
Exposure to asbestos can cause permanent damage to the mesothelium. Asbestos is a powerful carcinogen. Over time, asbestos fibers in the body cause the mesothelial cells to become malignant and form a cancerous tumor known as mesothelioma. Unfortunately, the widespread use of asbestos throughout the twentieth century has led to an epidemic of mesothelioma in the United States.