What does the pleural space contain?

The pleural space, which is the thin gap between the two layers of pleura surrounding the lungs, contains a small amount of fluid. This pleural fluid plays a crucial role in facilitating the movement of the lungs during breathing. The fluid creates a lubricated surface that reduces friction as the lungs expand and contract within the thoracic cavity. Additionally, this small amount of fluid helps maintain surface tension, which is essential for lung stability and proper function.

In contrast, the other options do not accurately describe the pleural space's contents. A large volume of air is not found in the pleural space, as this would indicate a pathology such as pneumothorax rather than normal anatomical function. Residual lung volume refers to the air remaining in the lungs after exhalation, which is not present in the pleural space. Blood and nutrients are also not components of the pleural space; instead, this space is specifically designed to contain the pleural fluid necessary for lung mechanics.