Any incident of tissue damage is followed by a process of epithelial and parenchymal repair. This repair procedure is extremely complex and so far not fully understood. In the airways, the repair (remodeling) process includes repair of the tight junctions, cell migration, cell differentiation and metaplasia, mitosis and hyperplasia of basal cells and mitotic redifferentiation, among other processes . It has been shown that smoke impairs lung repair mechanisms [49,50] and disrupts procedures that are able to restore the tissue structure. This may lead to peribronchial fibrosis and narrowing, particularly at the site of small airways. Fibronectin and TGF-b produced by the epithelial cells are involved in the normal repair processes, but there may be an excess of factors that cause fibrosis and abnormal remodeling [39,51].
In summary, the pathogenesis of COPD is extremely complex, and until the mechanisms that are involved become more clear, it is difficult to understand why only 20% of smokers develop COPD.
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