Immune System & Defences

• Physical and chemical barriers

  Stop pathogens from getting into the body
• Immune system


  Destroys pathogens that do make it into the body
• Skin


  • Acts as a physical barrier that pathogens can't get through
  • Secretes oils and antimicrobial substances that can kill pathogens
• Nose


  Has hairs and mucus that trap pathogens and particles in the air
• Trachea and esophagus


  Only two tubes leaving the throat that pathogens can enter
• Trachea, bronchi, and bronchioles


  1. Covered in mucus that traps particles

  2. Lined with cilia that move mucus and trapped particles up to the throat to be swallowed
• Stomach acid


  Hydrochloric acid that kills most pathogens by lowering pH to around 2
• White blood cells


  • Continually patrol the body
  • Have three important functions: phagocytosis, producing antitoxins, and producing antibodies
• Phagocytosis


  Process where white blood cells consume and destroy pathogens
• Antitoxins


  Small molecules produced by white blood cells that bind and counteract toxins produced by pathogens
• Antigens


  Substances detected by the immune system as foreign, such as bacterial cell walls or viral proteins
• Antibodies


  Small proteins made by white blood cells that can bind to specific antigens and signal for their destruction
• Immune system remembers pathogens


  Produces many antibodies quickly to destroy pathogens before they can develop
• The body survives millions of pathogens attacking it every day