Mesothelium cells begin as the mesoderm during development (the lungs derive from endoderm) and apparently play an important part in the development of the lung. A membrane of flat cells that lines the body cavity of embryos and forms the squamous cells of the peritoneum, pericardium, and pleura.
The mesothelium tissues are the layer (membranes) that surround and protect organs of the chest, abdominal cavity, and pelvis.
The Mesothelium is divided into three primary regions
The peritoneum – The peritoneum includes the layers of mesothelium lining the abdominal cavity. This region is also divided into two layers. The visceral peritoneum lines the internal organs, and the parietal peritoneum, which lines the abdominal and pelvic walls.
The pleura – The pleura are the two membranes which form a lining around the lungs. This, in turn, is divided into the visceral pleura which lies directly over the lungs, and the parietal pleura, which is the outer layer of the lung lining.
The pericardium – The pericardium refers the mesothelium that forms a lining around the heart and the mediastinum, the area in the chest between the lungs.
Functions of the Mesothelium
It was once thought that the only purpose of the mesothelium was to provide a slippery, non-sticky surface in order to protect the organs of the chest and abdominal cavity during movement and breathing.
We are now learning, that similar to the tonsils and appendix, the mesothelial has other important functions as well, and functions as a dynamic membrane rather than simply being a border that allows smooth movement. These include:
The transport and movement of fluids and matter across the membrane from the outer aspects of the chest and abdominal cavities to the internal organs. In regulating these activities, the mesothelial tissues may play an important role in homeostasis (balance) of the body.
Coagulation (blood clotting)
Immune function – The mesothelium appears to have a protective role both against infection as well as the spread of tumors. Pleural mesothelial cells secrete substances which are active against bacteria, including those responsible for tuberculosis.
Protection against tumors – Mesothelial tissue appears to secrete substances that inhibit the growth of digestive tract tumors. These substances appear to inhibit the ability of cancer cells to “stick” to the mesothelium, and as such, decrease the spread or metastasis of some tumors.
Medical Conditions Involving the Mesothelium
Mesothelioma is a type of cancer that begins in the mesothelium (in any region where mesothelial is present.) This cancer is most common in people who have been exposed to asbestos (see asbestos dangers,) and continues to increase in incidence worldwide. Mesothelioma Causes and Risk Factors
Symptoms of mesothelioma may include a cough, difficulty swallowing, abdominal pain and bloating, and other symptoms depending upon the location of the tumor. A surgical procedure called pleurodesis (removal of the pleura) is sometimes performed to remove the tumor, though the prognosis is usually poor by the time this cancer is diagnosed.
Adhesions are a common complication after abdominal surgery. Scar tissue involving the mesothelioma in the abdominal cavity may create bands of tissue, which in turn can trap the bowel and cause obstruction. Symptoms of adhesions are often abdominal pain, cramping, and bloating. When adhesions are mild (not causing a complete obstruction) people may suffer from chronic intermittent episodes of abdominal pain, especially after eating large meals.
Pleural effusions – Pleural effusions or a build-up of fluid in the cavity between the two layers of the pleura (the pleural mesothelial) are influenced by substances secreted by pleural mesothelial cells.
Fibrosis – Researchers are currently investigating the role which the pleural mesothelium may play in fibrosis, particularly conditions such as idiopathic pulmonary fibrosis.