Goblet cells secrete mucus. The mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli.
The cilia are hair-like structures on the surface of the epithelial cells. They beat the mucus secreted by the goblet cells. This moves the mucus (plus the trapped microorganisms and dust) upward away from the alveoli towards the throat, where it's swallowed. This helps prevent lung infections.
Elastic fibres help the process of breathing out. On breathing in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to help push…