Disease, Defence and Treatment

• Microorganisms


  • Most microorganisms are harmless, some are even beneficial
  • Microorganisms that cause diseases are called pathogens
• Pathogens

  • Fungi
  • Protists
  • Viruses
  • Bacteria
• Ways pathogens can be spread

  • Contact
  • Body fluids
• Body defences

  • Skin forms a barrier that makes it difficult for pathogens to enter
  • Intact skin is a barrier and blood clots around wounds
  • Stomach acid and lysozyme in tears protect where skin is not present
• Immune system

  White blood cells manage the body's response to pathogens
• Types of white blood cells

  • Phagocytes
  • Lymphocytes
• Phagocytes

  • Engulf and digest pathogens
• Lymphocytes

  • Produce antibodies to neutralise pathogens
• Drug development

  1. Preclinical drug trials

  2. Testing on human cells grown in the laboratory

  3. Testing on animals

  4. Testing on healthy human volunteers

  5. Clinical trials

  6. Testing on small group of patients
• Placebo

  Inactive substance given instead of a drug in a drug trial
• Blinded trial

  Patients do not know if they have been given the drug or placebo, but the doctors know
• Double-blinded trial

  Neither patients nor doctors know which patient has been given the drug or the placebo, only the researchers know
• Immunity and vaccinations

  1. Lymphocyte recognises antigen of invading microorganism

  2. Lymphocyte produces specific antibody to neutralise the organism

  3. Lymphocyte divides rapidly producing many clones all producing the same antibody

  4. Once microorganism is destroyed, most antibody-producing cells die off except a few which become memory cells

  5. If the same microorganism is encountered again, the memory cells rapidly produce large numbers of antibodies to destroy it before symptoms develop
• Vaccination involves introducing a dead, weakened or part of a pathogen to stimulate the immune system to produce antibodies against that pathogen
• Preventing spread of diseases

  1. Use disposable gloves

  2. Use condoms

  3. Proper hygiene (hand washing, cleaning hospital wards)
• Antibiotics

  Destroy bacteria or stop their growth
• Antibiotics work only on bacteria and fungi, they do not kill viruses
• Some antibiotic resistant bacteria like MRSA are causing problems in hospitals, this may have developed from overuse of antibiotics
• Penicillin, an antibiotic, was discovered by Alexander Fleming and was made by a fungus
• Now antibiotics are chemically modified and synthetic