What is a true statement about the pleural sac?

What is a true statement about the pleural sac?

• A. It is an air-filled space connected to the atmosphere
• B. It surrounds both lungs and maintains positive pressure
• C. It contains a large volume of surfactant for lung protection
• D. It is a closed sac around each lung containing only a small volume of lubricating fluid

Answer: (D)

The correct statement about the pleural sac is that it is a closed sac around each lung containing only a small volume of lubricating fluid. The pleural sac, or pleural cavity, plays a crucial role in respiratory mechanics. It is filled with pleural fluid, which acts as a lubricant, reducing friction between the lungs and the thoracic wall during breathing. This fluid also helps to create a negative pressure environment that is essential for lung expansion and contraction. The structure of the pleural sac is vital for facilitating proper inflation of the lungs. This negative pressure is achieved because the pleura is typically a closed system that does not connect directly to the outside atmosphere. This unique anatomical arrangement helps maintain lung tension and ensures that when the chest cavity expands, the lungs follow suit due to the cohesive forces created by the pleural fluid. Surfactant is indeed present in the lungs, specifically in the alveoli, where it reduces surface tension to prevent alveolar collapse. However, the pleural sac itself does not contain a large volume of surfactant. The other options all describe incorrect characteristics of the pleural sac, reinforcing the importance of understanding its true nature and function in the respiratory system.

The correct statement about the pleural sac is that it is a closed sac around each lung containing only a small volume of lubricating fluid. The pleural sac, or pleural cavity, plays a crucial role in respiratory mechanics. It is filled with pleural fluid, which acts as a lubricant, reducing friction between the lungs and the thoracic wall during breathing. This fluid also helps to create a negative pressure environment that is essential for lung expansion and contraction.

The structure of the pleural sac is vital for facilitating proper inflation of the lungs. This negative pressure is achieved because the pleura is typically a closed system that does not connect directly to the outside atmosphere. This unique anatomical arrangement helps maintain lung tension and ensures that when the chest cavity expands, the lungs follow suit due to the cohesive forces created by the pleural fluid.

Surfactant is indeed present in the lungs, specifically in the alveoli, where it reduces surface tension to prevent alveolar collapse. However, the pleural sac itself does not contain a large volume of surfactant. The other options all describe incorrect characteristics of the pleural sac, reinforcing the importance of understanding its true nature and function in the respiratory system.