**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.