And then those pathogens either can be swallowed through our esophagus and end up in our highly acidic and highly deadly environment inside our stomach which can ultimately kill off that pathogen or we can expel that pathogen or harmful substance via the process of spitting. Now, inside the nasal cavity, we also have actual tiny hairs. And what these hairs actually do is they can help trap our dust particles and other particles inside the nasal cavity before it actually goes into our lungs. Now, if we check out this structure, which are basically these saclike structures where gas exchange actually takes place within the alveoli of our lungs, we have specialized immune cells known as the alveolar macrophages. And these are specialized cells that can engulf and digest any harmful agent and substance that the cell actually comes across. Now, we also have something called airway constriction.