B6 - Preventing and treating disease

• Skin defences against pathogens


  • physical barrier to infection
  • produces antimicrobial secretions
  • microorganisms that normally live on the skin prevent pathogens growing
• Defences in the nose


  • Cillia and mucus trap particles in the air, preventing them from entering the lungs
  • Trachea and bronchi produce mucus, which is moved away from the lungs to the back of the throat by cilia, where it is expelled
• Stomach defences

  • Produces strong acid (pH 2) that destroys pathogens in mucus, food and drinks
• White blood cells


  • If a pathogen enters the body, the immune system tries to destroy the pathogen
  • The function of white blood cells is to destroy pathogens
  • There are two main types of white blood cell - lymphocytes and phagocytes
• Lymphocytes 


  • Antitoxins
  • lymphocytes produce antitoxins that bind to the toxins produced by pathogens
  • this neutralises the toxins
  • Antibodies
  • lymphocytes produce antibodies that bind to antigens on the surface of the pathogen
  • this helps to destroy them
• Phagocytes


  • Phagocytes are attracted to an area of infection
  • The phagocyte surrounds the pathogen and engulfs it
  • Enzymes that digest and destroy the pathogen are released
• Herd immunity


  If a large proportion of a population is vaccinated against a disease, the disease is less likely to spread, even if there are unvaccinated indivuals in the population
• Vaccination

  • Small quantities of a dead or inactive form of a pathogen are injected into the body
  • This stimulates lymphocytes to produce the correct antibodies for that pathogen
  • Once the pathogens have been destroyed, memory cells remain that can quickly reproduce the complementary antibody
  • If the same pathogen re-enters the body, the correct antibodies can be produced quickly to prevent infection
• Treating disease - antibiotics


  • Antibiotics can kill bacteria in the body
  • Specific bacteria need to be treated by specific antibiotics
  • Some bacteria can become antibiotic resistant and therefore not affected by antibiotics which can be dangerous
• Treating viral diseases


  • Antibiotics do not affect viral diseases
  • Drugs that kill viruses often damage the body's tissue
  • Painkillers treat the symptoms of viral diseases but do not kill the pathogen
• New drugs are trialled for:

  • toxicity - is it harmful?
  • efficacy - does it work?
  • dose - what amount is it safe and effective to administer?
• Where does digitalis come from?


  Foxglove plants
• Where does aspirin come from?


  Willow trees
• Where does penicillin come from?

  Penicillium mould (discovered by Alexander Fleming)
• Stages of clinical trials

  • Pre-clinical trials
  • Clinical trials
  • Peer review
  • Double-blind trials
• Pre-clinical trials


  • Drug is tested in a lab on cells, tissues and live animals
• Clinical trials


  • Healthy volunteers recieve very low doses to test whether the drug is safe and effective
  • If safe, larger numbers of healthy volunteers and patients recieve the drug to find the optimum dose
• Peer review


  Before being published, the results of clinical trials will be tested and checked by independant researchers
• Double-blind trials


  • Some patients are given the drug, and some are given a placebo
  • Neither the patient nor the doctor knows who has been given the placebo
  • This reduces biases in the trial
• Producing monoclonal antibodies


  • Mice are injected with a specific antigen to stimulate the production of the lymphocytes that produce the specific complementary antibodies
  • Lymphocytes produce antibodies but cannot replicate to form clones
  • The lymphocytes are extracted and fused with tumour cells to form hybridoma cells
  • A hybridoma cell can produce antibodies and replicate rapidly to form clones, all of which produce antibodies
  • After a large amount of hybridoma cells have been produced, they are collected and purified (the tumour cells are removed) for use
• Use of monoclonal antibodies in research


  • Since monoclonal antibodies are specific to a single binding site on a single antigen, they can be used to target specific molecules in cells and tissues by binding fluorescent dye to them
• Use of monoclonal antibodies in treatment


  They can deliver toxic chemicals and drugs specifically to cancer cells, limiting their harm to other cells in the body
• Culturing microorganisms


  • Bacteria multiply by binary fission
  • Under the optimal conditions, the number of bacteria can double every twenty minutes
  • Bacteria can be grown in a solution (nutrient broth) or as colonies on an agar gel plate
  • Good aseptic technique is important to prevent contamination of the bacteria cultures
• Before culturing

  • Sterilise culture media and agar before use
  • Ensures no contamination in the media
  • Wipe bench/table with disinfectant
  • Kills any microorganisms on the surface
  • Pass inoculating loop through a blue Bunsen flame and allow to cool slightly
  • Sterilises the inoculating loop
• Loosen the lid on the bacteria culture bottle and dip the inoculating loop in the culture


  • Lift the lid as little as possible when dipping the innoculating loop
  • Reduce the chances of contamination of the culture by microorganisms from the air
• Inoculate the agar gel plate by streaking the inoculating loop across the surface of the agar


  • Lift one side of the agar gel plate's lid as little as possible when inoculating the agar
  • Reduces the chance of contamination of the agar by organasims from the air
• Tape the lid shut and place the inoculated agar gel plate in an incubator


  • Do not create an airtight seal when taping the lid on
  • Prevents anaerobic pathogens from growing
  • Do not incubate at temperatures higher than 25 degrees C
  • Reduces growth of human pathogens whose optimum temperature is human body temperature (37 degrees C)
  • Incubate plates with the surface of the agar facing downwards
  • Stops condensation from dripping on the agar and spreading contamination
• After culturing


  • Pass inoculating loop through a blue Bunsen flame and place on a heatproof mat to cool
  • Sterilises the inoculating loop
  • Wipe bench/table with disinfectant
  • Kill any microorganisms on the surface
• Pregnancy tests


  • Urine is applied to the end of the stick
  • The test strip contains monoclonal antibodies that are specific to HCG - a hormone only produced by pregnant women - with a dye attached
  • The liquid moves up the strip and if HCG is present, the antibodies bind to immobilised antibodies in the test zone and cause a line of blue dye to appear in the result window
  • The control window contains immobilised antibodies that are specific to the mobile antibodies and a line of dye apppears there if the mobile antibodies are present to show that the test is valid, even if HCG is not present