Respiratory system - en

The upper respiratory includes the nasal cavity and pharynx . Air enters the nasal cavity through the external nares and passes through the narrow channels (meati) created between the nasal conchae . This exposes the air to the mucosa which warms and moistens the air as it passes through the entire system. The mucosa also removes particulates, dust, pollen, etc. and moves it toward the esophagus. In the nasal cavity the respiratory mucosa is partly ciliated and partly non ciliated and the cilia beat downward. The upper portion of the nasal cavity has olfactory receptors whose nerves pass through the foramina in the cribriform plate to the olfactory bulb of the brain.

The nasal cavity narrows at the internal nares before joining with the pharynx. The pharynx is divided into three portions: the nasopharynx , the oropharynx and the layngopharynx which connect to the nasal cavity, oral cavity and larynx respectively. The nasopharynx has the pharyngeal tonsils (lymph nodes) and the opening into the eustachian canal (a.k.a. pharyngotympanic tube or
internal auditory canal). This canal allows equalization of pressure between the atmosphere and the middle ear. This is important when increasing or decreasing in altitude and when atmospheric pressure changes for any reason. Inability to equalize pressure can impair hearing as occurs when the mucosa is inflamed due to a respiratory infection. The lining continues to be ciliated into the nasopharynx and then changes to non-keratinized stratified squamous in the oropharynx and
laryngopharynx where protection from ingested food is important.