− | Air is inhaled and passes through the upper respiratory tract (nares, [[Nasal cavity - Anatomy & Physiology|nasal cavity]], nasopharynx, larynx, trachea) where it is heated and moistened. It then passes to the lower respiratory tract (bronchi, bronchioles, alveoli) where oxygen diffuses across the alveolar wall and into the blood, forming oxyhaemoglobin. | + | Air is inhaled and passes through the upper respiratory tract (nares, [[Nasal cavity - Anatomy & Physiology|nasal cavity]], [Nasopharynx - Anatomy & Physiology|nasopharynx]], larynx, trachea) where it is heated and moistened. It then passes to the lower respiratory tract (bronchi, bronchioles, alveoli) where oxygen diffuses across the alveolar wall and into the blood, forming oxyhaemoglobin. |