Air enters the body through the nose and passes through the nasal cavity, which is lined with a mucous membrane and fine hairs (cilia) to help filter out foreign bodies, as well as to warm and moisten the air.

Paranasal sinuses are hollow air-containing spaces within the skull that communicate with the nasal cavity. They have a mucous membrane lining and their function is to provide the lubricating fluid - mucus, as well as to lighten the bones of the skull and help produce sound.

THE PHARYNX

After passing through the nasal cavity, the air next reaches the pharynx (throat). There are three divisions of the pharynx.

The nasopharynx is the first division, and it contains the adenoids, which are collections of lymphatic tissue. The adenoids (also known as the pharyngeal tonsils) are more prominent in children, and if enlarged, they can obstruct air passageways.

Before the nasopharnyx and closer to the mouth is the second division of the pharynx, the oropharynx. The palatine tonsils, two rounded masses of lymphatic tissue, are located in the oropharynx.

The third division of the pharynx is the hyopharynx (also caleld the laryngopharynx). It is in the hypopharyngea region of the pharynx, serving as a common passageway for food from the mouth and air from the nose.