Gli esseri umani possono respirare sia dalla bocca che dal naso, perché sia l'una che l'altro si aprono nella faringe; la via migliore è comunque quella nasale tramite la quale l'aria viene pre-riscaldata e liberata dalle impurità più grossolane passando attraverso i meandri nasali. Tramite le coane l'aria passa poi nella faringe e quindi nella laringe .
La laringe è posta sotto l'osso ioide, ed è formed by a cartilaginous skeleton consists of several parts (one of them is the ' epiglottis which closes the larynx during swallowing, regulating the entry of air and food). These cartilages are connected by ligaments and muscles. The larynx is lined by mucous membrane. In the field larynx are the vocal cords , equal and symmetrical folds, which are present in pairs on each side, they vibrate the air flow that emit sounds that are then modulated with the help of the lips and tongue.
inspired air then passes into the trachea , a channel about 12 cm long cylinder with a diameter of 20 mm. Inside is lined by an epithelium mucosal equipped with cilia that vibrate in the opposite direction to that of air, contrasting the entry of dust into the airways.
The trachea is divided at the fourth thoracic vertebra in two main bronchi, right and left. The 2 bronchi penetrate the lung mass and branching, while by cartilage in constant decline. The bronchioles are thinner and the branches are said to have breathing when the walls with saccular dilatation: the alveoli. The bronchioles end in dead-end and are called infundibulum. While all of the respiratory epithelium and eyelashes, that of the alveoli is thin and lacking in monolayer ciglia. 
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