Some respiratory diseases caused by Aspergillus


Dr Walter Blyth

Date: 7 September 2001


The Aspergilli are inhaled in the form of spores(conidia) and to a lesser extent of hyphal fragments released from colonised substrates such as grain and decaying plant remains. Histologically, all mammalian lungs have a gross similarity. From the trachea downwards generations of airways of progressively diminishing size lead eventually to the alveoli in which the primary lung function of gaseous exchange takes place. In the larger bronchi, which are supported by cartilage, submucosal glands secrete mucus augmented by lysozyme and IgA. Further mucus is added by goblet cells which are a component of the columnar layer of ciliated cells lining the bronchial lumen. The upwardly directed beating of the cilia propels the mucus towards the larynx from which it is swallowed or expectorated. The mechanism is generally referred to as the mucociliary escalator. Submucosal glands are absent from the remaining lower levels of the airways and only a few goblet cells occur in the ciliated epithelia of bronchioles. The integrity of the lumina of bronchioles downwards is assured by the occurrence of smooth muscle as far as the respiratory bronchioles. At the level of the respiratory bronchioles, alveoli first make their appearance and become prolific at the alveolar ducts.

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