I think that it protects them because they like swish them about and make them covered by a mucusy layer which then protects them further called bronchilus. this eventully stops any damage at all in the alveoli
At the top of the respiratory system, the nostrils (also called nares) act as the air intake, bringing air into the nose, where it's warmed and humidified. Tiny hairs called cilia protect the nasal passageways and other parts of the respiratory tract, filtering out dust and other particles that enter the nose through the breathed air. :D hope it helps
Alveoli
alveoli
Alveoli
They push the foreign particles out wards. This helps to protect your lungs from damage by the particles.
It is the lining of the alveoli that acts as our respiratory surface.
The lining has to thicken in order to protect the egg that is released.
To protect the fetus
alveoli sacs <--nova net.
A lining in a pipe, placed there to protect the material of the pipe from the contents that will be passing through the pipe.
You can use a combination of things like heavy duty lining for the curtain fabric, interior or exterior blinds, interior or exterior shutters, a reflective film on the window glass. For comprehensive details see this article: http://www.helium.com/items/1714551-how-to-protect-curtains-and-drapes-from-sun-damage
The fluid lining the inner alveolar membrane is called surfactant. It helps reduce the surface tension in the alveoli, which prevents them from collapsing in on themselves every time we exhale.