What are the Pleura of the Lungs?

Anatomy and Function of the Pleural Membranes

diagram of the pleura in anatomy
What are the pleura?. A.D.A.M. Medical Encyclopedia

Definition: Pleura

The pleura refers to the two membranes that cover the lungs and line the chest cavity. The purpose of the pleura is to cushion the lungs during respiration.

The pleural cavity is the space between these two membranes and contains pleural fluid.

Structure of the Pleura

The pleura are made up of two layers:

  • The visceral pleura is the thin slippery serous membrane that covers the surface of the lungs, dipping into the areas separating the different lobes of the lungs (the area known as the hilum.)
  • The parietal pleura is the outer membrane of the pleura which lines the inner chest wall and the diaphragm.

The visceral and parietal pleura join at the hilum of each lung, the area where the major bronchi, as well as pulmonary arteries and veins, enter each lung.

Between the pleura lies the pleural cavity. This space contains around three to four teaspoons of fluid.

Function of the Pleura

The pleura glide past each other via the lubrication of the pleural space, allowing the lungs to actively expand during inspiration and relax during exhalation. If the pleura become scarred, or if fluid builds up in the space between these membranes it can restrict this gliding movement of the lungs within the pleura.

Conditions Involving the Pleura

There are several conditions which can involve the pleura as well as the pleural space between the two layers of the pleura. Pain due to inflammation of the pleura is often felt as sharp and varies with inspiration.

Pain which worsens with a deep breath (and is usually sharp in character) is referred to as pleuritic chest pain. Some conditions involving the pleura include:

Pleurisy - Pleurisy refers to an inflammation of the pleural membranes. When these layers become inflamed, the surfaces become rough and sticky.

This can lead to sharp pains with breathing.  Pleurisy is most commonly caused by viral infections but can be caused by bacterial infections and autoimmune diseases such as rheumatoid arthritis and lupus. For example, pleurisy may occur with lupus when antibodies attack the pleura resulting in inflammation.

Pleural Effusion - In a pleural effusion, excess fluid collects in the pleural space. When the amount of fluid accumulates rapidly or is large, breathing can be hampered. Congestive heart failure is the most common cause of a pleural effusion, but there are many possible causes. When a pleural effusion is small, your doctor may simply observe it to see if it goes away.When a pleural effusion is large and hampering the expansion of the lungs it can cause significant shortness of breath and often needs to be drained. This is usually done with a procedure known as a thoracentesis, in which a long fine needle is inserted through the chest wall into the pleural space to withdraw the fluid.

Often times a pleural effusion recurs. When this happens, a shunt may be placed to the outside of the body so that fluid can periodically be drawn off, or a procedure called a pleurodesis may be done. This involves inserting a chemical between the layers of the pleura which caused inflammation, in turn causing the layers of the pleura to stick together so that fluid can no longer accumulate.

Malignant Pleural Effusion - A malignant pleural effusion refers to an effusion in which cancer cells are present.  This can be due to lung cancer or spread (metastases) to the lungs from other cancers such as breast cancer. Malignant pleural effusions are often treated like benign pleural effusions, with drainage of the fluid and measures to prevent fluid from accumulating or allowing the fluid to periodically be drained via a shunt.

Mesothelioma - Pleural mesothelioma is the most common type of mesothelioma. This cancer, which arises in the pleura, is most commonly caused by occupational exposure to asbestos. These cancers are often discovered when the cancer has already spread, but when caught early are often treated with a procedure called a pleurectomy.

Pneumothorax - In a pneumothorax, air collects in the pleural cavity. It may be caused by trauma to the chest, chest surgery, and COPD among other causes. When a pneumothorax is small, it may simply be observed to see if the air is reabsorbed. With a larger pneumothorax, it is necessary to place a chest tube to allow the air to escape and the lungs to reexpand.

Hemothorax - A hemothorax refers to blood in the pleural cavity which can occur during chest surgery or trauma.

Treatment

Treatment of pleurisy will depend upon the underlying cause. When air (as in a pneumothorax) blood (as in a hemothorax) or fluid (as in a pleural effusion) accumulate in the pleural space, a chest tube is often placed to remove the air, fluid, or blood.

Sources:

Batra, H., and V. Antony. Pleural mesothelial cells in pleural and lung diseases. Journal of Thoracic Disease. 2015. 7(6):964-80.

Bertin, F., and J. Deslauriers. Anatomy of the Pleura: Reflection Lines and Recesses. Thoracic Surgery Clinics. 2011. 21(2):165-171.

National Heart, Lung, and Blood Institute. What are Pleurisy and Other Pleural Disorders? Updated 09/21/11. https://www.nhlbi.nih.gov/health/health-topics/topics/pleurisy

U.S. National Library of Medicine. MedlinePlus. Pleural Disorders. Updated 01/17/17. https://medlineplus.gov/pleuraldisorders.html

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