Body Defences

• The human body has many natural defences against pathogens.
• Mechanical barriers:

  • Nostrils contain hairs that help trap dust
  • Skin has a thick outer layer of dead cells
• Chemical barriers:

  • Sticky mucus which can trap pathogens
  • In the stomach, hydrochloric acid is secreted which kills many of the bacteria in food
• Cells: Pathogens that manage to get through all these defences are usually destroyed by white blood cells:

  • Some of these cells take in and digest the pathogens by phagocytosis
  • Others produce antibodies that incapacitate or kill the pathogen
  • Vaccination against disease helps antibodies to produce very quickly