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- A maxillary sinus in each cheek
- Between six and 12 ethmoid sinuses on each side of the nose between the eyes
- A frontal sinus on each side in the forehead
- A pair of sphenoid sinuses behind the ethmoid sinuses
Each sinus has an opening, called an ostium, which connects it to the nose.
The sinuses, except for the frontal sinuses, begin in the fetus as pea-sized air pockets that grow through childhood until they are roughly walnut sized.
Purposes of the Sinuses
The sinuses lighten the skull or improve our voices, but their main function is to produce a mucus that moisturizes the inside of the nose. This mucus layer protects the nose from pollutants, micro-organisms, dust and dirt. Tiny hair cells called cilia move the layer of mucus slowly backward into the throat, where it is swallowed.
The nose and the sinuses are closely linked by the ostium. The nose is divided into two cavities by the nasal septum. The superior, middle and inferior turbinates are rounded projections that run the length of the nasal cavity along the side of the nose. The area between each turbinate is called a meatus. The sinuses drain via the ostium into the meatus areas between each turbinate, with the different types of sinus draining into different areas.