•The function of the respiratory system is to move two gases: oxygen and carbon dioxide. Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them.

•The respiratory system has built-in methods to prevent harmful substances in the air from entering the lungs. Hairs in your nose help filter out large particles. Microscopic hairs, called cilia, are found along your air passages and move in a sweeping motion to keep the air passages clean.

•As air passes through the nasal cavities it is warmed and humidified, so that air that reaches the lungs is warmed and moist.