What is the function of the pleural membranes?

• A. They create a lubricated cavity that reduces friction and keeps the lungs inflated by surface tension
• B. They produce surfactant in alveoli
• C. They regulate gas exchange by oxygen saturation
• D. They filter lymph from interstitial fluid

Answer: (A)

The pleural membranes create a thin, lubricated pleural cavity between the lungs and the chest wall. This lubrication reduces friction during breathing, allowing the lungs to slide smoothly as the thorax expands and contracts. At the same time, the pleural fluid and the opposing elastic forces of the lungs and chest wall generate a slight negative intrapleural pressure, along with surface tension in the fluid, that helps keep the lungs stretched open and pressed against the chest wall. That combination keeps the lungs inflated and functioning through each breath.

Surfactant production happens in the alveoli, not the pleura, so that’s not a pleural function. Gas exchange is driven by diffusion across the alveolar-capillary membranes, not by the pleura. Filtering lymph is a job of the lymphatic system, not the pleural membranes.