The ethmoid and maxillary sinuses are present at birth, but the frontal and sphenoid sinuses do not become aerated until 6 or 7 years of age. The sinuses are lined primarily by ciliated columnar epithelium and connect with the nasopharynx via narrow ostia. Normally, the epithelium is coated by a double layer of mucus: a viscid gel layer superficially and a more fluid layer underneath. Resistance to infection depends on the patency of the ostia, the function of the ciliary mechanism, and the quality of the secretions.
Obstruction of the ostia results either from mucosal swelling or, less commonly, mechanical obstruction. By far the most frequent offenders are viral upper respiratory infection and allergic inflammation. Less common causes include cystic fibrosis, trauma, choanal atresia, deviated septum, polyps, foreign body, and tumor.
Factors that impair normal mucociliary function include viral infections, cold or dry air, certain chemicals or drugs, and, rarely, inborn errors of motility. Alterations of the mucus occur in asthma and cystic fibrosis.
The bacteria that cause sinusitis often colonize the nasopharynx of healthy children. Disruptions in one or more of the barriers described above allow these organisms to ascend through the ostia and multiply within the sinuses.
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.