The bodys natural defences

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The bodys natural defences

  1. 1. The Body’s Natural Defences
  2. 2. The Body’s Natural Defences • Our body fights harmful microbes every day • Microbes must fight through three levels of our body’s defences before they can cause us harm • The first line of defence • The second line of defence • The third line of defence
  3. 3. The First Line of Defence
  4. 4. The First Line of Defence The Respiratory System Our Skin The Eyes Tears produce chemicals called enzymes which can kill some Mucas and tiny hairs in the nose Stops microbes entering the stop microbes entering of the eye microbes on the surface our lungs body unless it is cut or damaged We sometimes sneeze or cough these harmful microbes away from our body
  5. 5. The Second Line of Defence
  6. 6. The Second Line of Defence Non Specific White Blood Cells Red blood cells: The blood contains Carry iron and oxygen around the body White blood cells: Help fight infection Plasma: Liquid which carries the blood cells around the body
  7. 7. The Second Line of Defence Non Specific White Blood Cells The blood flows around the body in one direction only
  8. 8. The Second Line of Defence Non Specific White Blood Cells If the skin gets damaged, microbes can enter the blood stream and make us ill
  9. 9. The Second Line of Defence Non Specific White Blood Cells The White Blood Cells called ‘phagocytes’ notice anything foreign or strange that gets through the first line of defence and move towards that ‘foreign object’
  10. 10. The Second Line of Defence Non Specific White Blood Cells The phagocytes then surround and destroy the foreign object or, in this case, microbe www.csulb.edu/depts/biology/media/cell751.gif
  11. 11. The Third Line of Defence
  12. 12. The Third Line of Defence Specific White Blood Cells All invading cells have distinctive antigens on their surface When the specific white blood cell comes across a microbe, it will a) Make an antibody to match that microbes antigen b) Tell all the other specific white blood cells to make lots of that antibody
  13. 13. The Third Line of Defence Specific White Blood Cells The body’s antibodies find their matching antigen on the harmful microbes and lock on to them
  14. 14. The Third Line of Defence Specific White Blood Cells The antibodies will then a) Mark the harmful microbes for destruction b) Stay in the blood after the harmful microbes have been killed ready to fight them if they should ever return

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