Cigarette smoke contains chemicals known as polycyclic aromatic hydrocarbons and nitrosamines, which are powerful carcinogens. They cause the release of enzymes from some types of white blood cells (neutrophil granulocytes and macrophages), which destroy elastin and lead to lung damage. They are also linked with impaired DNA-repair, which increases the risk of developing lung cancer. These chemicals can increase the permeability of the lining (epithelium) of the small airways and allow easier access for the carcinogens.
Cigarette smoke increases the volume of glands, hence secretions (mucus) in large airways. It also raises the number of goblet cells, which secrete mucus in the glands. Cigarette smoke increases the number and distribution of goblet cells in small airways too. Increased mucus production in the lungs is one of the causes of chronic (long-term) cough in smokers.
Chronic inflammation of the large airways results from cigarette smoking. Cigarette smoke activates lipid peroxidation and modifies collagen, which is a type of proteins in the connective tissues of your lungs. Lipid peroxidation can cause direct cell damage. Modified collagen stimulates adhesions and activation of macrophages in the airways, causing inflammation and destruction of cells. This process eventually leads to the development of emphysema. Cigarette smoke is associated with worsening of bronchial asthma.
The lining of your airways contains cilia, which are thin, microscopic, hairlike protuberances. They move rhythmically to expel excessive secretions from your airways. Cigarette smoking damages cilia directly and inhibits ciliary beat frequency too. This process is linked with repeated episodes of bronchitis and lower respiratory tract infections (LRTI). The function of immune cells of the respiratory tract (pulmonary alveolar macrophages) is inhibited by smoking (especially by tar and smoke particles), reducing the immunity and increasing the risk of LRTI further. There is a significant relationship of smoking history to pneumonia. Cigarette smoke can increase the severity, frequency, and natural history of other respiratory diseases as well. It causes increased risk and severity of tuberculosis.
Cigarette smoking raises the risk of pulmonary embolism, which can be a lethal condition because it increases the risk of blood clot formation in the deep veins of the body (deep-vein thrombosis/DVT). Some of the clots can travel via blood and block the main artery of your lung or its branches (pulmonary embolism). Affected part of the lung, usually dies due to impaired blood flow.
Passive smokers may have impaired lung function described as small airway disease. They have a higher risk of developing lung cancer. Yearly, 3000 lung cancer deaths occur in non-smokers due to passive smoking in USA. Passive smoking causes increased risk of developing bronchial asthma, bronchitis, and pneumonia in infants.
- Bronchitis – Inflammation of the large and mid-sized airways in the lungs
- Carcinogens – Agents, which can cause cancer.
- Elastin – A protein, which is in the connective tissues.
- Emphysema – A type of chronic obstructive pulmonary disease (COPD), which occurs due to progressive chronic inflammation and narrowing the airways of the lungs, causing difficulty breathing.
- Lipid peroxidation – Oxidative degradation of lipids (Free radicals take electrons from the lipid molecules in cell membranes, causing cell damage).
- Macrophages – A type of immune cells
(Photo courtesy: Ed Schipul)