Paranasal sinuses are air-filled spaces, communicating with the nasal cavity, within the bones of the skull and face.
Types in humans
Humans possess a number of paranasal sinuses, divided into subgroups that are named according to the bones within which the sinuses lie:
The paranasal air sinuses are lined with respiratory epithelium (ciliated pseudostratified columnar epithelium).
Paranasal sinuses form developmentally through excavation of bone by air-filled sacs (pneumatic diverticula) from the nasal cavity. This process begins prenatally, and it continues through the course of an organism's lifetime
Sinuses in animals
Paranasal sinuses occur in a variety of animals (including most mammals, birds, non-avian dinosaurs, and crocodilians). In non-humans, the bones occupied by sinuses are quite variable.
The biological role of the sinuses is debated, but a number of possible functions have been proposed:
- Decreasing the relative weight of the front of the skull, and especially the bones of the face.
- Increasing resonance of the voice.
- Providing a buffer against blows to the face.
- Insulating sensitive structures like dental roots and eyes from rapid temperature fluctuations in the nasal cavity.
- Humidifying and heating of inhaled air because of slow air turnover in this region.
The paranasal sinuses are joined to the nasal cavity via small orifices called ostia. These become blocked easily by allergic inflammation, or by swelling in the nasal lining which occurs with a cold. If this happens, normal drainage of mucus within the sinuses is disrupted, and sinusitis may occur.
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