The airways

The respiratory system is built to take in the oxygen life processes need and remove the carbon dioxide they produce.

Figure to be added

Figure 6.7 — the human respiratory system: nasal cavity, mouth, pharynx, larynx, trachea, bronchus, bronchioles, ribs, chest and diaphragm.

Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli

Mucus keeps the walls of the nasal cavity moist, and the back of it is lined with cilia. Bacteria and dust in the air stick to the mucus, so they do not reach the lungs; the beating cilia carry them out, and they are also removed with saliva when we sneeze or cough.

What the nose does to the air

It moistens it.
It warms it to body temperature.
It removes particles from it.