Britannica Sources used in this answer

How do the pleural membranes allow the lungs to move during breathing?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — human respiratory system The lungs serve as the gas-exchanging organ for the process of respiration.

The pleural membranes facilitate lung movement during breathing through a combination of structural design and pressure dynamics. The thoracic cavity is lined by the parietal pleura, while the lungs are covered by the visceral pleura.12

These two membranes are kept in close proximity by a thin film of extracellular fluid, which acts as a lubricant. This fluid creates surface tension that bonds the membranes together, allowing the lungs to slide smoothly along the thoracic wall during breathing.123

Furthermore, the lungs are maintained in apposition to the chest wall by a negative (below-atmospheric) pressure within the pleural space. This pressure is a result of the opposing elastic forces of the lungs, which tend to collapse, and the chest wall, which tends to expand. By keeping the lungs distended against the thoracic wall, this system ensures that as the chest cavity expands during inspiration, the lungs expand with it, increasing their volume.243