Trachea have cartillage rings which support it. And the Alveoli has large surface area for diffusion and its moist and thin.
Alveoli are surrounded by capillaries so that the oxygen can diffuse into the blood and carbon dioxide can diffuse out. I think it depends on the shape of the alveoli to the path of the capillary.
Chondromalacia
Alveoli does not collapse because lungs always have a residual volume which prevents the alveoli to collapse.
It protects the articular cartliage.
it is a stout
alveoli
catrilage covers the ends of bone and reduces the friction between them.
Alveoli
alveoli
Alveoli alveoli - air sacs in your lungs
Alveoli