− | Air is inhaled and passes through the upper respiratory tract (nares, 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, 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. |