Upper airway
The respiratory system can be structurally segregated into the upper and lower respiratory airways. The upper airways are comprised of the nose, nasal cavity, and pharynx.
The Nose
The nose has a portion that is external and an internal portion inside the skull. It is composed by an upper framework of bone, a series of cartilages in the lower part, with a small zone of fibro-fatty tissue forming the lateral margin of the nostril. It is divided into two by the nasal septum.
The nasal cavity
The nasal cavity begins with the nostrils to the choanae, The choanae are the oval-shaped openings lying between the nasal cavities and the nasopharynx .
Pharynx
The pharynx is a half tube shaped musculofascial passage linking the oral and nasal cavities at the head to the larynx and esophagus at the neck. The pharyngeal cavity forms a common pathway for air and food.