In simple terms, your nasal cavity (or nose in laemens terms) is filled with many many little hairs. Your nose also contains glands that produce mucus. Your hairs in the nose filters out the air and the mucus traps debris and bacteria, which forms boogers. Next, your trachea (or your windpipe that leads to the lungs) is lined with mucus and cilia to also trap dust, bacteria, and other gunk that’s in the air to prevent it from reaching the primary bronchioles (the section of the lungs that branch out at the end of the trachea and lead into the alveoli).
In summary, your respiratory system is filled with cilia and mucus to filter the air you breath, and to trap bacteria and other gunk in the air.
