What is the primary function of the pleura?

The primary function of the pleura is to serve as a double-walled serous membrane that encloses each lung. This structure facilitates smooth movement of the lungs during respiration. The pleura consists of two layers: the visceral pleura, which directly covers the lungs, and the parietal pleura, which lines the thoracic cavity. The space between these two layers, known as the pleural cavity, contains pleural fluid that reduces friction as the lungs expand and contract. This function is essential for efficient breathing and helps prevent any damage to lung tissues due to friction with the chest wall during inhalation and exhalation.

Other options relate to different structures or functions within the body. For example, a cover for the abdominal organs refers more accurately to the peritoneum, not the pleura. A lining for the thoracic cavity hints at a broader context that includes the parietal pleura, but it does not fully capture the specific purpose of enclosing the lungs. A protective layer for the heart describes the pericardium, which serves a similar protective role for the heart but operates independently of the pleural system. Thus, the correct answer most accurately defines the defining anatomical and functional aspects of the pleura.