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Anatomy and physiology of the mesothelium

Mesothelial cells are flat cells that produce a small amount of lubricating fluid. A layer of mesothelial cells form a membrane that lines body cavities and covers the outer surface of most of the body’s internal organs. The lining formed by the mesothelial cells is called the mesothelium or mesothelial membrane.

The mesothelium commonly lines the inside of the chest, the abdomen and the space around the heart (pericardium). Malignant mesothelioma most commonly starts in mesothelial cells in the pleura, followed by the peritoneum.



The body has 2 pleural cavities in the chest, and each cavity contains a lung. The cavities are lined with a mesothelial membrane called the pleura or pleural membrane. The pleura is made up of 2 continuous layers:

  • visceral pleura (inner pleura)
    • The visceral pleura covers the outer surface of the lung and sticks (adheres) to all its surfaces. It clings to the lung fissures, which separate the lobes of the lung, so that each lobe is also covered with visceral pleura.
  • parietal pleura (outer pleura)
    • The parietal pleura lines the chest wall and extends over the diaphragm and mediastinum. The diaphragm is the thin muscle below the lungs and heart that separates the chest cavity from the abdomen. The mediastinum is the space in the chest between the lungs, breastbone and spine that contains structures such as the heart, blood vessels, trachea (windpipe), esophagus and lymph nodes.

The area between the 2 layers of pleura is called the pleural space. There is normally only a small amount of fluid in the pleural space.

Blood vessels, bronchi, nerves and the pleura come together at the entrance of the lung, called the hilum. Bronchopulmonary lymph nodes, which help drain lymph fluid from the lungs, are located here. The neck and chest contain many other lymph nodes that also help drain lymph fluid from the lungs and other structures in the chest:

  • Scalene lymph nodes are located at the base of the neck.
  • Supraclavicular lymph nodes are located above the collarbone.
  • Internal mammary lymph nodes are located inside the chest, behind and around the breastbone (sternum).
  • Subcarinal lymph nodes are located around the windpipe (trachea).
  • Hilar lymph nodes are located in the chest where the bronchus enters the lung.
  • Mediastinal lymph nodes are located around the mediastinum.
  • Bronchopulmonary lymph nodes are located around the bronchi (large tubes, or airways) within the lung.


The mesothelial membrane that covers the abdominal organs and lines the abdominal and pelvic walls is called the peritoneum. The peritoneum is made up of 2 layers:

  • The visceral peritoneum covers and supports most of the internal abdominal organs.
  • The parietal peritoneum lines the wall of the abdomen and pelvis.

A narrow fluid-filled space separates the parietal peritoneum from the visceral peritoneum.


The mesothelial membranes help protect organs by making a special lubricating fluid that allows the organs to move around.


The pleura help protect and cushion the lungs. The lubricating fluid that fills the pleural space allows the 2 layers of the pleura to slide easily over each other and makes it easier for the lungs to move inside the chest when we breathe.


The peritoneum helps protect the organs in the abdomen and keeps them in place. It also makes a lubricating fluid that helps organs move smoothly against each other inside the abdomen as we move around.


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