**5. Etiopathogenesis**

The etiopathogenesis of COPD involves interplay of several over-lapping and co-existing injuries, defects, inflammation and disorganized repair in a vicious cycle, ultimately leading to a chronic progressive impairment of lung function. These processes are shared by other airway and parenchymal diseases of lungs and aggravated by other pulmonary and systemic co-morbidities. The key steps involved are epithelial injury, inflammatory cell activation, protease-antiprotease imbalance, airway inflammation, goblet cell hypertrophy and hypersecretion, recurrent infection, acute exacerbations, attempts to disorganized repair and fibrosis, ultimately leading to chronic progressive permanent airway obstruction(Barnes,2008;Kasahara & Tuder,2000;MacNee & Tuder,2009;Rennard,2003 as cited in Shapiro SD,2010).
