There are many different size alveolus () in our lungs and they are connected each other. Why don't the big alveolus burst and the small alveolus collapse?
Alveoli are highly elastic structures. They do not resist surface tension, which allows the surface tension to deflate the alveoli during exhalation. Lung cells release surfactant that lowers surface tension and keeps the alveoli from collapsing after exhalation.