What are the two factors that reduce lung volume?

1. Surface Tension: The surface tension of the fluid lining the alveoli creates an inward force that tends to collapse the lungs. This occurs because the liquid-air interface within the alveoli creates surface tension, which acts like a stretched elastic band trying to pull the alveoli inward. It requires a certain amount of pressure inside the lungs to counteract this surface tension and keep the alveoli open.

2. Elastic Recoil: The elastic properties of the lung tissue itself contribute to lung volume reduction. Lung tissue contains elastic fibers that recoil and try to collapse the lungs. These fibers are stretched when the lungs are inflated and generate a retractive force when the lungs are at rest. This elastic recoil of lung tissue provides a counterbalancing force against surface tension, helping maintain the alveoli open.