The pleural space is a narrow area within the chest cavity, surrounding each lung. It is a key part of the respiratory system, enabling effective lung function. Normally filled with a small amount of fluid, this space facilitates lung movement and overall respiratory mechanics.
Anatomy and Location
The pleural space exists between two layers of thin, serous membranes known as the pleura. The inner layer, called the visceral pleura, directly covers the surface of the lungs, extending into the lung’s fissures. The outer layer, the parietal pleura, lines the inside of the chest wall, including the diaphragm and the mediastinum, which is the central compartment of the chest. These two pleural layers are continuous with each other at the hilum of each lung, where structures like blood vessels and airways enter and exit.
The term “potential space” highlights that in a healthy state, the visceral and parietal pleura are almost touching, with minimal separation. This close proximity is maintained by a thin film of serous pleural fluid, which acts as a lubricant. In a healthy human, this fluid typically measures a few milliliters (10 to 20 mL). This small volume is continuously produced and reabsorbed, ensuring constant lubrication.
The Role in Respiration
The pleural fluid within the pleural space is fundamental to breathing mechanics. It functions as a lubricant, allowing the visceral and parietal pleura to glide smoothly as the lungs expand and contract. This frictionless movement enables effortless respiration.
Beyond lubrication, the pleural fluid creates strong surface tension. This tension causes the visceral pleura to adhere closely to the parietal pleura lining the chest wall. As the diaphragm contracts and the rib cage expands during inhalation, the chest wall moves outward. Due to this adhesion, the lungs are passively pulled along, expanding to draw air inward.
The pleural space consistently maintains a negative pressure, lower than the atmospheric pressure outside the body. This negative pressure counteracts the natural tendency of the lungs to recoil and collapse, keeping them inflated for efficient gas exchange.
Disruptions to the Pleural Space
When the integrity or normal function of the pleural space is compromised, it can significantly impair breathing. The accumulation of substances like air, excess fluid, or blood disrupts the delicate negative pressure and the close adhesion between the pleural layers.
One common disruption is a pneumothorax, where air enters the pleural space. This air buildup creates pressure that can cause the lung to partially or completely collapse, leading to symptoms like chest pain and shortness of breath.
Another issue is pleural effusion, which involves an abnormal accumulation of fluid. This excess fluid compresses the lung, hindering its ability to expand fully and resulting in difficulty breathing, cough, and chest discomfort.
Similarly, a hemothorax occurs when blood collects in the pleural space, often due to injury. The presence of blood exerts pressure on the lung, potentially causing it to collapse and leading to symptoms such as chest pain and breathing difficulties.