Question

Name the main force responsible for inhalation and the main two forces responsible for exhalation (in mammals).

Answer 1

Alveoli expand during inhalation, taking in fresh oxygen, and shrink during exhalation, expelling carbon dioxide from the body.  

Expiration- Two of the main forces that work to collapse alveoli are the elastic properties of the lung itself and the surface tension of the water which partially occupies the inside of alveoli. These collapsing forces are crucial to exhale air after an inspiration but must be countered at end expiration to prevent the alveoli from collapsing completely.

Inspiration- One of the principal forces that prevent alveolar collapse is the extensive collagen extracellular matrix (ECM) running throughout the interalveolar septa, formed by fibroblasts in the interstitium. The ECM provides "radial traction": forces pulling in all directions away from the center of each alveolus, keeping it inflated.