Which statement about the pleural membrane is correct?

The pleural membrane is a crucial component of the respiratory system, and its primary role is to line the thoracic cavity and cover the lungs. This two-layered membrane consists of the visceral pleura, which adheres to the surface of the lungs, and the parietal pleura, which lines the inner wall of the thoracic cavity. The space between these two layers, known as the pleural cavity, contains pleural fluid, which serves to reduce friction during breathing and helps maintain proper lung expansion and contraction.

Understanding the function of the pleural membrane sheds light on why it does not serve the purposes suggested by the other statements. For instance, it does not have a role in protecting the heart from infections, because that responsibility falls to other structures, such as the pericardium. The pleural membrane also does not secrete hormones; instead, respiration is regulated by various systems involving hormones released elsewhere in the body. Lastly, although the pleura is essential for respiratory function, it has no involvement in the digestive process. Thus, the correct answer reflects the anatomical and functional characteristics of the pleural membrane in the context of the respiratory system.