Inside the lining of the airways are glands called, "submucosal glands", and above them, closer to the opening in the airway are cells called "goblet cells" - because they are shaped kind of like a goblet, which is a type of cup. The submucosal glands and the goblet cells make mucous which helps protect the inside of the airways. The mucous in the airways of healthy lungs is a thin film which traps irritants such as dust particles and pollen so they do not damage the airways and keep them from entering the air sacs (alveoli).