In addition to gas exchange, the lungs and the other parts of the respiratory system have important jobs to do related to breathing. These include:

• Bringing all air to the proper body temperature.
• Moisturizing the inhaled air for necessary humidity.
• Protecting the body from harmful substances by coughing, sneezing, filtering or swallowing them, or by alerting the body through the sense of smell.
• Defending the lungs with:
  • cilia - microscopic hairs along the air passages
  • phlegm (mucus or sputum) - a moving carpet of phlegm collects dirt and germs inhaled into the lungs and moves them out to be coughed up or swallowed
  • macrophages - scavenger cells in the lungs that literally eat up dirt and germs invading the lungs