And this includes the nasal cavity inside our nose the trachea, the windpipe as well as the bronchi and our bronchioles. So along these air passageways we have specialized types of cells called goblet cells. And these goblet cells basically secrete a special type of slimy and mucus like material we call the mucus membrane. So the air passageways of our body essentially are line with this mucus membrane. And when we breathe in air and we breathe in these different types of pathogens, these pathogens ultimately are trapped inside that mucus. Now, inside the air pathogeways we also have these hair like projections we call cilia.