Human defence systems

• Non-specific defences - physical and chemical barriers that stop pathogens from entering the body
• Specific immune response- the immune systems targeted attack on pathogens that get past the first defences
• The body has both general barriers and specialised immune responses to fight infections
• Defence system: Skin

  How it works: Acts as a physical barrier to prevent pathogens from entering

  Example: Cuts form scabs to seal wounds
• Defence system: Nose

  How it works: Contains hairs and mucus that trap pathogens

  Example: Prevents microbes from entering the lungs
• Defence system: Trachea and Bronchi

  How it works: Lined with mucus and cilia to trap and move pathogens away from the lungs

  Example: Cilia sweep mucus to the throat where it is swallowed
• Defence system: Stomach

  How it works: Contains hydrochloric acid that kills swallowed pathogens

  Example: Destroys bacteria in food and mucus
• If pathogens enter the body the immune system responds. White blood cells are key to this response.
• The method phagocytosis works when white blood cells engulf and digest pathogens using enzymes.
• The method antibody production works when white blood produce specific antibodies that attach to antigens on pathogens marking them for destruction
• The method antitoxin production works when white blood cells produce antitoxins to neutralise toxins released by bacteria
• First line (non-specific barriers) - skin, mucus, stomach acid, cilia
• Second line (immune responses) - white blood cells, antibodies, antitoxins