So, once again, mucous membrane within the trachea, the bronchi and the bronchioles, as well as within our nasal cavity, we have specialized cells called goblet cells. So these cells secrete a substance that forms a very sticky and slimy mucous membrane along the pathogeways within which our air actually moves. Now, when harmful particles and agents move with the air, they can get stuck within this mucus membrane. And the mucous membrane, as I mentioned earlier, is also found within our nasal cavity of the nose. Now, we also have tiny hairlike structures found along the cells lining the airways, and these can help carry the pollutants to our pharynx. So if we take a look at the diagram of our respiratory system, this is our trachea, these are the bronchi.