6.1 Defence mechanisms

6.1 Defence mechanisms

1. Any disease is an interaction between pathogen and body's defence mechanisms

   • Pathogen may overwhelm defences = individual dies
   • Body's defence mechanisms overwhelm pathogen = individual recovers from disease
     • Body's defences are better prepared for second infection from same pathogen
       • Body's defences can destroy pathogen before any harm is caused
         • Immunity

2. NON-SPECIFIC MECHANISMS

   • Respond to all types of pathogens
   • Act quickly and immediately
   • Form - barrier to entry of pathogens
   • Form - phagocytosis

3. SPECIFIC MECHANISMS

   • Distinguish between different pathogens
   • Less rapid
   • Involve lymphocyte (type of white blood cell)
   • Form - cell-mediated responses involving T lymphocytes
   • Form - humoral responses involving B lymphocytes
   • Immunity

4. RECOGNISING YOUR OWN CELLS

   • Lymphocytes need to distinguish body's own cells & chemicals from foreign ones
   • In foetus, lymphocytes constantly colliding with other cells
     • In foetus, lymphoctes only collide with body's own cells and chemicals
       • Infection in foetus is rare because of protection from outside world
       • Some lymphocytes have receptors that fit with those of body's own cells
         • These lymphocytes either die or are suppressed
           • Remaining lymphocytes are those that fit foreign material and so only respond to foreign material

5. Lymphocytes

   • Specific lymphocytes already exist
     • Not produced in response to an infection
   • Lymphocytes have protein on its surface complementary to one of the proteins of pathogen
   • Infection occurs
     • Specific lymphocytes with complementary proteins stimulated to increase numbers so that it can be effective in destroying the pathogen
       • Causes time lag between exposure to pathogen and body's defences bringing it under control