‘Smokers suffer from more lower respiratory tract infections.’ Justify this statement in light of respiratory tract protection mechanisms.

Smoke contains many harmful chemicals and carcinogens (such as polycyclic aromatic hydrocarbons). There are several ways in which smoking increases the likelihood of lower respiratory tract infections.
1)   Chemicals paralyse the cilia (i.e. damaged muco-ciliary escalator). This leads to poor removal of pathogens. Thus  infection is more likely.2)   Chemicals stimulate production of more mucus. Pooled mucus provides a focus for infection.3)   Carcinogens can lead to cancer. The tumour can block parts of the respiratory tract. Pooled secretions distal to the blockade act as a focus for infection.4)   Chemicals lead to alveolar damage resulting in emphysema. Emphysema is a risk factor for pneumonia, particularly H. Influenza pneumonia.5)   Smokers are more likely to suffer from Myocardial Infarction and Stroke. Thus, more likely to be relatively immobile in a susceptible environment (i.e. hospitals). Therefore, more likely to get chest infections.