What is the mesothelium and mesothelioma?

The mesothelium is a thin membrane which covers most of the internal organs of the human body and has the function to protect them. It consists of two layers of cells: The first one immediately surrounds the organ and the other one forms a kind of sac around it. The mesothelium produces a greasing fluid which is released between these two layers in order to allow moving organs (e.g. the beating heart, the expanding & contracting lungs etc.) to glide easily against adjoining structures.
Depending on where exactly the mesothelium is located in the body is has different names. In the abdominal cavity most of the organs are covered by the so called peritoneum. The mesothelial tissue that protects and surrounds the lungs and lines of the wall of the chest cavity is the pleura. The pericardium covers the heart. The male internal reproductive organs are surrounded by a tissue called tunica vaginalis testis. The womans internal reproductive organs are covered by the tunica serosa uteri.
Mesothelioma is a disease in which cells of the mesothelium become abnormal and divide without order or control, so it is a rare form of cancer which produces malignant cells.

These cells can damage and invade adjacent tissues and organs. In the worst case they can spread (metastasize) from their origin to nearly every other part of the body. The beginning of most of the cases lies in the pleura or in the peritoneum.