The Bodys Natural Defences The Bodys 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
The First Line of Defence
The First Line of Defence The Respiratory Our Skin System The Eyes Tears produce chemicals called enzymes which can kill some Mucas andmicrobes tiny hairsentering in the nose Stops the microbes on theentering surface our of the eye stop microbes lungs body unless it is cut or damaged We sometimes sneeze or cough these harmful microbes away from our body
The Second Line of Defence
The Second Line of Defence Non Specific White Blood Cells (Phagocytes) 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
The Second Line of Defence Non Specific White Blood Cells (Phagocytes) The blood flows around the body in one direction only
The Second Line of Defence Non Specific White Blood Cells (Phagocytes) If the skin gets damaged, microbes can enter the blood stream and make us ill
The Second Line of Defence Non Specific White Blood Cells (Phagocytes) 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’
The Second Line of Defence Non Specific White Blood Cells (Phagocytes) The phagocytes then surround and destroy the foreign object or, in this case, microbe www. csulb. edu/depts/biology/media/cell 751. gif
The Third line of Defence
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
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
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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