The pleural space is an area within the chest cavity that plays a direct role in the mechanics of breathing. This specialized region is a thin, fluid-filled gap situated between the lungs and the inner wall of the thorax. It is a protective and functional boundary that allows the lungs to expand and contract efficiently with every breath. Understanding its delicate structure and purpose helps explain why its disruption can seriously impact respiratory function.
Anatomical Structure and Location
The pleural space exists as a potential gap between two distinct layers of protective membrane called the pleurae. The inner membrane, known as the visceral pleura, adheres directly to the entire surface of the lung, following its contours and extending into the fissures that divide the lung into lobes. This membrane is continuous with the outer layer at the root of the lung, where airways and vessels enter the organ.
The outer layer, called the parietal pleura, lines the internal surface of the chest wall, including the ribs, the diaphragm, and the mediastinum. Because the two layers are separated only by a very thin film of liquid, the pleural space is described as a potential space rather than an open cavity. This arrangement ensures that the lungs are suspended within the thoracic cavity while remaining closely linked to the movement of the chest wall.
Normal Function of the Pleural Space
The function of this space relies on the presence of a small volume of serous pleural fluid, which continuously lubricates the pleural membranes. This fluid enables the visceral and parietal layers to slide smoothly past one another with minimal friction as the lungs inflate and deflate during respiration. This lubrication prevents damage to the delicate lung tissue from rubbing against the interior of the chest wall.
More significantly, the pleural fluid creates surface tension that pulls the two pleural layers together. This force, combined with the opposing tendencies of the chest wall to expand outward and the lungs to recoil inward, maintains a pressure within the space that is slightly lower than the pressure inside the lungs. This sub-atmospheric pressure acts like a suction, mechanically coupling the lungs to the chest wall so that when the chest expands during inhalation, the lungs are passively pulled outward and expand along with it.
Conditions Caused by Pleural Compromise
When the integrity of the pleural space is compromised, the mechanics of breathing are immediately affected. The introduction of air into the space, known as a pneumothorax, destroys the necessary sub-atmospheric pressure. This loss of pressure allows the lung’s natural elastic recoil to take over, causing it to shrink or collapse away from the chest wall, which severely impairs the ability to exchange oxygen.
Pneumothorax can occur spontaneously, sometimes in healthy individuals due to the rupture of small air sacs on the lung surface, or it can be caused by trauma, such as a rib fracture or a penetrating chest wound. Procedures like central line insertion can also inadvertently breach the pleural barrier, allowing air to escape from the lung or enter from outside the body.
Another common disruption is a pleural effusion, the abnormal accumulation of excess fluid in the space. This can result from a failure of the body’s fluid balance, such as in cases of heart or kidney failure, where pressure pushes too much fluid out of the blood vessels. Alternatively, it can be caused by local inflammation or disease, such as infection or malignancy, which increases fluid production. Regardless of the cause, the excess fluid compresses the lung tissue, hindering its ability to fully expand and leading to shortness of breath.