Respiratory (airway) passages are cavities and tubes connected in series with each other, through which air containing oxygen from the environment reaches the lungs. Distinguish between upper and lower respiratory tract. The upper airway begins with a nasal cavity, which is divided into two halves by a septum. Having passed through the nasal cavity, air enters the pharynx, and then into the larynx, from which the lower respiratory tract begins. The larynx is formed by several cartilages. A special epiglottis cartilage (epiglottis) covers the entrance to the larynx when food is swallowed. From the larynx, air enters the trachea. The trachea is formed by 16-20 cartilaginous half-rings, thanks to which a food lump can freely pass through the esophagus, adjacent to the trachea behind. Approximately at the level of the 5th thoracic vertebra, the trachea branches into two bronchi, formed by cartilaginous rings. The bronchi enter the right and left lungs. In the lungs, they repeatedly branch into smaller tubes, forming a bronchial tree. The thinnest bronchial branches are called bronchioles. The thinnest passages depart from them, the walls of which form numerous protrusions – alveoli, or pulmonary vesicles.
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