Nasal cavity consists of vestibule, respiratory region and olfactory region.
Nasopharynx proximal is lined with respiratory epithelium and distally, where it is continuous with oral part of pharynx, is lined with stratified squamous nonkeratinized epithelium. Larynx is located between pharynx and trachea and it consists of epiglottis and vocal folds. Trachea is approximately 11 cm. This smooth muscle is composed of right and left spirals. Further branching or ramifications or bronchi give rise to different orders of the bronchial tree.