Question

Distending pressure and surface tension are two farces that act upon the alveoli at all times. Outline how these forces are offset in an alveolus at end-expiration and end inspiration?

Answer 1

• Alveoli are lined with a thin layer of fluid called surfactant which is a mixture of phospholipids that reduce surface tension and increase lung compliance
• alveoli of the lungs are highly elastic, they do not resist surface tension on their own, which allows the force of that surface tension to deflate the alveoli as air is forced out during exhalation by the contraction of the pleural cavity.
• The intercostal muscles relax, returning the chest wall to its original position. During exhalation, the diaphragm also relaxes, moving higher into the thoracic cavity. This increases the pressure within the thoracic cavity relative to the environment
• pulmonary surfactant that is secreted by type II alveolar cells. ... Advantages of pulmonary surfactant are that it lowers surface tension of alveolar lining-decreases the inspiratory work of breathing and it preferentially lowers surface tension in small alveoli-stabilizes alveolar units.
• During expiration the equal pressure point moves toward the alveoli and collapsible small airways. The lung volume decreases, leading to smaller alveoli with less alveolar elastic recoil.