Cigratte smokes is injurious to health of lungs.

*Cigrarette smokes contains high concentration of free radicals( reactive nitrogen species, reactive oxygen species(ROS)) , which leads to intrease oxidative and nitrosative stress on lungs .

• Lipid peroxidation of cell membrane thus damage to alveolar epithelium
• ROS oxidize methionine residue of α₁-antitrypsin ——→α₁-antitrypsin becomes inactive
• ↓ Anti-protease activity → ↑ elastase activity-Elastase digests alveolar elastic tissue
• Results in: Loss of lung elasticity, alveolar wall destruction.