Human defence systems

• Your skin covers your body and acts as a barrier. It prevents bacteria and viruses reaching the tissues beneath. Your skin produces antimicrobial secretions to destroy pathogenic bacteria
• Healthy skin is covered with microorganisms that help keep you healthy and act as an extra barrier to the entry of pathogens
• Your nose is full of hairs and produce mucus which traps pathogens
• The trachea and bronchi also secrete mucus that traps pathogens and the lining of the tubes is covered in cilia - tiny hair like projections from cells. The cilia beat to waft the up to the back of the throat where it is swallowed
• The stomach produces acid and this destroys the microorganisms in the mucus you swallow and the pathogens in food and drink
• The second line of defence is the immune system; made up of white blood cells
• White blood cells get rid of microbes in 3 ways:

  1. They engulf (eat) the microbes through phagocytosis
  2. They make antibodies which neutralises microbes or make them stick together, thus destroying them
  3. They make antitoxins to neutralise the toxins (poisons) produced by microbes
• Once a white blood cell has destroyed a pathogen, your white blood cells will recognise the pathogen the next time it invades the body and produce the right antibodies quickly before it can make you ill