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The Body’s Natural Defences

The Body’s Natural Defences. 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.

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The Body’s Natural Defences

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  1. The Body’s Natural Defences

  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. The First Line of Defence

  4. Our Skin The Respiratory System The Eyes Tears produce chemicals called enzymes which can kill some microbes on the surface of the eye Stops microbes entering the body unless it is cut or damaged Mucus and tiny hairs in the nose stop microbes entering our lungs We sometimes sneeze or cough these harmful microbes away from our body The FirstLine of Defence

  5. The Second Line of Defence

  6. TheSecondLine of DefenceNon Specific White Blood Cells Red blood cells: Carry iron and oxygen around the body The blood contains White blood cells: Help fight infection Plasma: Liquid which carries the blood cells around the body

  7. TheSecondLine of DefenceNon Specific White Blood Cells The blood flows around the body in one direction only

  8. TheSecondLine of DefenceNon Specific White Blood Cells If the skin gets damaged, microbes can enter the blood stream and make us ill

  9. TheSecondLine of DefenceNon 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. The SecondLine of DefenceNon 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. The Third Line of Defence

  12. TheThirdLine of DefenceSpecific 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 microbe’s antigen b) Tell all the other specific white blood cells to make lots of that antibody

  13. The ThirdLine of DefenceSpecific White Blood Cells The body’s antibodies find their matching antigen on the harmful microbes and lock on to them

  14. The ThirdLine of DefenceSpecific 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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