Bronchogenic carcinoma (lung cancer)
Lung cancer is often initiated by irritants to the bronchi. Excessive mucus production and inactivity of the cilia allow these irritants to enter the lungs resulting in alveolar tissue damage (emphysema). Subsequently, the lower respiratory tract is invaded by squamous cancer cells which spread, causing more and more damage.
Bronchitis is caused by the inflammation of the lining of the bronchioles. This may be due to infection by bacteria or viruses , or chemicals such as those found in tobacco smoke.