Preventing and treating disease

• Non-specific defences of the human body against all pathogens


  • Skin
  • Nose
  • Stomach
• Skin


  • Physical barrier to infection
  • Produces antimicrobial secretions
  • Microorganisms that normally live on the skin prevent pathogens growing
• Nose


  • Cilia 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


  Produces strong acid (pH 2) that destroys pathogens in mucus, food and drinks
• If a pathogen enters the body, the immune system tries to destroy the pathogen
• White blood cells


  • Function is to fight pathogens
  • Two main types are lymphocytes and phagocytes
• Vaccines have saved countless lives
• Despite occasional side effects, vaccines are safe
• Antibiotics are used to treat bacterial infections
• Antivirals are used to treat viral infections
• Types of white blood cells

  • Lymphocytes
  • Phagocytes
• How lymphocytes fight pathogens

  1. Produce antitoxins that bind to toxins produced by pathogens to neutralise them

  2. Produce antibodies that target and help destroy specific pathogens by binding to antigens on their surfaces
• Antitoxin


  Lymphocytes produce these to bind to toxins produced by some pathogens (usually bacteria) and neutralise them
• Antibody


  Lymphocytes produce these to target and help destroy specific pathogens by binding to antigens (proteins) on the pathogens' surfaces
• Antigen


  Proteins on the surface of pathogens that antibodies bind to
• How phagocytes fight pathogens

  1. Attracted to an area of infection

  2. Surround the pathogen and engulf it

  3. Release enzymes that digest and destroy the pathogen
• Phagocyte


  White blood cells that engulf and destroy pathogens
• 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 individuals
• It is a common misconception that antibiotic resistance arises when people become resistant to a drug. In reality, it is the bacteria that evolve resistance.
• Key terms


  • antibiotic
  • efficacy
  • antibody
  • antigen
  • mucus
  • peer review
  • antitoxin
  • placebo
  • cilia
  • dose
  • toxicity
  • penicillin
• Most modern cures for diseases involve vaccination, which stimulates the immune system to produce the correct antibodies.
• Antibiotics


  Medicines that can kill bacteria in the body
• Specific bacteria need to be treated by specific antibiotics
• Antibiotics have greatly reduced deaths from infectious bacterial diseases, but antibiotic-resistant strains of bacteria are emerging
• Antibiotics


  Do not affect viruses
• Drugs that kill viruses

  Often damage the body's tissues
• Painkillers


  Treat the symptoms of viral diseases but do not kill pathogens
• Discovering and developing new drugs

  1. Drugs were traditionally extracted from plants and microorganisms

  2. Most modern drugs are now synthesised by chemists in laboratories
• Drugs extracted from plants and microorganisms

  • the heart drug digitalis comes from foxglove plants
  • the painkiller aspirin originates from willow trees
  • penicillin was discovered by Alexander Fleming from Penicillium mould
• Vaccination


  Involves injecting small quantities of dead or inactive forms of a pathogen into the body
• Vaccination


  • Stimulates lymphocytes to produce the correct antibodies for that pathogen
  • If the same pathogen re-enters the body, the correct antibodies can be produced quickly to prevent infection
• Stages of clinical trials

  1. Pre-clinical trials: Drug is tested in cells, tissues, and live animals

  2. Clinical trials: 1. Healthy volunteers receive very low doses to test whether the drug is safe and effective, 2. If safe, larger numbers of healthy volunteers and patients receive the drug to find the optimum dose
• Peer review


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


  Some clinical trials give some of their patients a placebo drug, and neither the patients nor the doctors know who has been given the real drug and who has been given the placebo
• Double-blind trials reduce biases in the trial
• The immune system is made up of white blood cells, antibodies, lymph nodes, spleen, thymus gland, bone marrow, and the complement system.
• Antibodies are proteins that bind to specific antigens on pathogens or foreign substances and trigger an immune response.
• White blood cells are involved in phagocytosis (engulfment) and killing invading microorganisms.
• What non-specific systems does the body use to prevent pathogen getting into it?

  skin;cilia and mucus in the nose, trachea, and bronchi; stomach acid
• What three functions do white blood cells have?

  phagocytosis, producing antibodies, producing antitoxins