The first line of defense

• Immune system


  The body system that prevents and fights disease, made up of many organs, tissues, and cells working together
• The immune system fights both infectious diseases, like measles, and non-infectious diseases, like cancer
• Lines of defence of the immune system

  • First line of defence
  • Second line of defence
  • Third line of defence
• First line of defence

  1. System of barriers to prevent pathogens from entering the body

  2. Pathogens must make it past the first line of defence before they can cause an infection
• First line of defence

  • Physical barriers stop pathogens from entering the body by blocking or trapping them
  • Chemical barriers kill pathogens before they can enter the body
• Physical barriers


  • Skin, mucus
• Chemical barriers


  • Stomach acid, enzymes in tears, saliva, and mucus
• Physical barriers like cilia

  Actively push pathogens out