During expiration, what is the role of elastic recoil in lung mechanics?

• A. To increase lung volume
• B. To decrease lung volume
• C. To stabilize lung pressure
• D. To assist in muscle contraction

Answer: (B)

During expiration, elastic recoil is crucial for decreasing lung volume. This phenomenon occurs because the lung tissues, along with the thoracic cavity, contain elastic fibers that stretch during inhalation when air fills the lungs. Once the inhalation phase is completed and the inspiratory muscles relax, these elastic fibers naturally want to return to their resting state.

As the elastic fibers recoil, they pull the lung tissues inward, leading to a reduction in lung volume. This decrease in volume helps to increase the pressure inside the lungs, allowing air to flow out of the lungs and into the atmosphere according to the principles of gas exchange and pressure gradients.

Understanding this concept is essential in comprehending how the mechanics of ventilation function, as it highlights the passive nature of expiration driven by elastic properties of lung tissue, as opposed to muscle contraction which primarily occurs during inhalation.