What does the pleural space refer to?

The pleural space is specifically defined as the area between the two layers of the pleural membrane, which is a thin layer of tissue that surrounds the lungs. This membrane consists of two parts: the parietal pleura, which lines the chest wall, and the visceral pleura, which covers the surface of the lungs. The pleural space contains a small amount of pleural fluid that serves as a lubricant, allowing the lungs to expand and contract smoothly during breathing without friction.

Understanding this definition is vital for comprehending respiratory physiology and the mechanics of breathing. The other options refer to different anatomical structures or areas that do not accurately represent the pleural space. The alveoli are smaller air sacs within the lungs where gas exchange occurs, the area surrounding the heart pertains to the pericardial sac, and the cavity where the ribs expand is related to the thoracic cavity as a whole, not specifically to the pleural space.