What Is the Pleura?

The pleura is a vital part of the respiratory tract. Its role is to cushion the lung and reduce any friction that may develop between the lung, rib cage, and chest cavity.

Each pleura (there are two) consists of a two-layered membrane that covers each lung. The layers are separated by a small amount of viscous (thick) lubricant known as pleural fluid.

There are a number of medical conditions that can affect the pleura, including pleural effusions, a collapsed lung, and cancer. When excess fluid accumulates between the pleural membranes, various procedures may be used to either drain the fluid or eliminate the space between them.

This article outlines what the pleurae are, what they do, and what conditions can affect them and impact respiratory health.

Anatomy of the Pleura

There are two pleurae, one for each lung, and each pleura is a single membrane that folds back on itself to form two layers. The space between the membranes (called the pleural cavity) is filled with a thin, lubricating liquid (called pleural fluid).

The pleura is comprised of two distinct layers:

• The visceral pleura is the thin, slippery membrane that covers the surface of the lungs and dips into the areas separating the different lobes of the lungs (called the hilum).
• The parietal pleura is the outer membrane that lines the inner chest wall and diaphragm (the muscle separating the chest and abdominal cavities).

The visceral and parietal pleura join at the hilum, which also serves as the point of entry for the bronchus, blood vessels, and nerves.

The pleural cavity is also known as the intrapleural space. It contains pleural fluid secreted by the mesothelial cells. The fluid allows the layers to glide over each other as the lungs inflate and deflate during respiration (breathing).

What the Pleura Do

The structure of the pleura is essential to respiration, providing the lungs with the lubrication and cushioning needed to inhale and exhale. The intrapleural space contains roughly 4 cubic centimeters (ccs) to 5 ccs of pleural fluid, which reduces friction whenever the lungs expand or contract.

The pleura fluid itself has a slightly sticky quality that helps draw the lungs outward during inhalation rather than slipping round in the chest cavity. It creates surface tension that helps maintain the position of the lungs against the chest wall.

The pleurae also serve as a division between other organs in the body, preventing them from interfering with lung function and vice versa.

Conditions That Affect the Pleura

A number of conditions can cause injury to the pleura or undermine its function. Harm to the membranes or overload of pleural fluid can affect how you breathe and lead to adverse respiratory symptoms.

Pleurisy

Pleurisy is inflammation of the pleural membranes. It is most commonly caused by a viral infection, but may also be the result of a bacterial infection or an autoimmune disease (such as rheumatoid arthritis or lupus).

Pleuritic inflammation causes the membrane surfaces to become rough and sticky. Rather than sliding over each other, they membranes stick together, triggering sharp, stabbing pain with every breath, sneeze, or cough. The pain can get worse when inhaling cold air or taking a deep breath. It can also worsen during movement or shifts in position. Other symptoms of pleurisy include fever, chills, and loss of appetite.

Pleural Effusion

A pleural effusion occurs when excess fluid accumulates in the pleural space. When this happens, breathing can be impaired, sometimes significantly.

Congestive heart failure is the most common cause of a pleural effusion, but there is a multitude of other causes, including lung trauma or lung cancer (in which effusion is experienced in roughly half of all cases).

A pleural effusion can be very small (detectable only by a chest x-ray or CT scan) or be large and contain several pints of fluid. Common symptoms include chest pain, dry cough, shortness of breath, difficulty taking deep breaths, and persistent hiccups.

Malignant Pleural Effusion

A malignant pleural effusion refers to an effusion that contains cancer cells. It's most commonly associated with lung cancer or breast cancer that has metastasized (spread) to the lungs.

Mesothelioma

Pleural mesothelioma is a cancer of the pleura that most often is caused by occupational exposure to asbestos. Symptoms include pain in the shoulder, chest or lower back, shortness of breath, trouble swallowing, and swelling of the face and arms.

Pneumothorax

Pneumothorax, also known as a collapsed lung, can develop when air collects in the pleural cavity. It may be caused by any number of things, including chest trauma, chest surgery, and chronic obstructive pulmonary disease (COPD). In addition to shortness of breath, there may be crepitus, an abnormal crackling sound from just under the skin of the neck and chest.

Spontaneous pneumothorax is a term used to describe when a lung collapses for no apparent reason. Tall, thin adolescent males are at the greatest risk for spontaneous pneumothorax, although females can also be affected. Risk factors include smoking, connective tissue disorders, and activities such as scuba diving and flying in which atmospheric pressure changes rapidly.

Hemothorax

Hemothorax is a condition in which the pleural cavity fills with blood, typically as a result of traumatic injury or chest surgery. Rarely, a hemothorax can happen spontaneously due to a vascular rupture.

The main symptom of hemothorax is pain or a feeling of heaviness in the chest. Others include a rapid heartbeat, trouble breathing, cold sweats, pale skin, and a fever, all indications that prompt medical attention is needed.