Category B - full version without watermark 720x576 (check terms and conditions at The version with watermark is for free to embed The functions of the nose are numerous and manifold. For proper working not only a normal structure but also a fully functional mucosa is important. As entrance to the respiratory tract the nose is above all responsible for cleaning, warming and humidification of the inspired air. To fulfill these important tasks, there is a special mucosa that is covered with a superficial layer of cilia and disposes of a tight network of blood vessels. The nasal mucosa lines not only the main cavity but also the paranasal sinuses. The latter consist of different cavities within the skull. They are called maxillary, ethmoid, frontal and sphenoid sinuses. They reach their full size only at adult age. The paranasal sinuses communicate with the main cavity of the nose via small ostia. Of particular importance is the middle meatus, which leads to the main cavitiy just below the middle turbinate and into which drain the maxillary and frontal sinuses as well as part of the ethmoid system. Anatomical changes or swelling of the mucosa due to a cold or an allergic rhinitis can lead to narrowing of the middle meatus. At a certain degree of constriction, ventilation and drainage of the paranasal sinuses are impaired. Such constellations can lead to a sinusitis.