The air spaces located inside the bone are called the paranasal sinuses (sinuses paranasales). They are lined with the respiratory epitheliums which usually consist of pseudostratified columnar ciliated epithelium. The direction of flow created by the ciliary beat is toward the ostium. During inspiration negative pressure is created which helps to facilitate drainage of the:
- Maxillary sinus (sinus maxillaris)
- Frontal sinus (sinus frontalis)
- Sphenoid sinus (sinus sphenoidalis)
- Ethmoidal labyrinth (labirynthus ethmoidalis)
- Mastoid air cells (cellulae mastoideae)
Paranasal sinuses have the following functions:
- Decreasing of the weight of the skull.
- Shock absorbing.
- Resonator of the voice.
- Warming and humidification of air.
- Regulation of intranasal pressure and serum gas pressures.
- Immune defense.