system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What actually happens to the dust and dirt that we inhale into our lungs everyday?

How does it get ever expelled if it sticks to the mucus walls?
gpt
Little hair-like structures called cilia constantly sweep the mucus lining upwards out of the initial respiratory tract (bronchus). Any dirt or dust that gets caught in the mucus in this step will eventually get swept out and enter the stomach.

Smoking damages these cilia which causes more particles to remain in the lungs.

Dirt and dust that get stuck deeper in your lungs will remain there forever. Your immune system will form a fiber scar over it to isolate it from your body.