Immune System & Defences

• Physical and chemical barriers

  • Skin acts as a physical barrier that pathogens can't get through
  • Skin also secretes oils and antimicrobial substances that kill the pathogens that rest on it
  • Noses have lots of hair and mucus to trap pathogens
  • The trachea, bronchi and bronchioles are all covered in a layer of mucus to further trap pathogens. To prevent mucus building up the trachea is also covered in cilia (tiny finger like protrusions) which slowly moves the mucus to back of the throat where we can swallow it
  • Our stomach produces hydrochloric acid (pH 2) which kills nearly all pathogens
• Despite our defences some pathogens will make it into our body
• White blood cells

  • Patrol the body in the bloodstream
  • Phagocytosis- tracking pathogens down, binding to them and then engulfing pathogens (this destroys them)
  • Produce antitoxins- small molecules to bind and counteract toxins
  • Produce antibodies- small proteins that lock onto antigens, act as signal to white blood cells (tell to destroy), specific to antigens. This means that our immune system can learn to defend against antigens its faced before and it can produce so many antibodies the antigen cannot fight back.
• An antigen is any substance that your body sees as foreign, which then causes your immune system to produce antibodies against it. For example, the toxins and cell walls of pathogens would be considered antigens. 
• Enzymes in tears act a barrier to stop pathogens
• The cells that line the trachea, bronchi and bronchioles have tiny hair-like projections that waft the mucus and pathogens away from the lungs, called cilia.
• Phagocytes are a special type of white blood cell. 
• Only phagocytes can carry out phagocytosis