Topic 5- Health and Disease

• Health


  A state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity
• Even if someone is very physically ill, they might not be considered unhealthy if, e.g. they have good mental health
• Communicable diseases


  Diseases that can be spread between individuals
• Non-communicable diseases


  Diseases that cannot be transmitted between individuals, such as cancer and heart disease
• If you are affected by one disease, it could make you more susceptible to others - your body may become weakened by the disease, so it's less able to fight off others
• Pathogens that cause communicable diseases

  • Viruses
  • Bacteria
  • Fungi
  • Protists
• Cholera

  A communicable disease caused by the bacterium Vibrio cholerae, with symptoms of diarrhoea
• Tuberculosis

  A communicable disease caused by the bacterium Mycobacterium tuberculosis, with symptoms of coughing and lung damage
• Malaria

  A communicable disease caused by a protist, which damages red blood cells and can cause severe illness
• Stomach ulcers


  A communicable disease caused by the bacterium Helicobacter pylori, with symptoms of stomach pain
• Ebola

  A communicable disease caused by the Ebola virus, with symptoms of haemorrhagic fever (a fever with bleeding)
• Chalara ash dieback


  A plant disease caused by a fungus that infects ash trees, leading to leaf loss and bark lesions
• How communicable diseases spread

  1. Via contaminated water sources

  2. Through the air when infected individuals cough

  3. Mosquitoes acting as vectors

  4. Oral transmission through contaminated food or water

  5. Via bodily fluids

  6. Carried through the air by the wind
• How to reduce transmission of communicable diseases

  1. Ensuring access to clean water

  2. Infected people avoiding crowded public spaces and practicing good hygiene

  3. Use of mosquito nets and insect repellent

  4. Having clean water supplies and hygienic living conditions

  5. Isolating infected individuals and sterilising contaminated areas

  6. Removing and replacing infected ash trees
• Viruses

  Microscopic organisms that can only reproduce inside living cells, taking advantage of the host cell's machinery
• Lytic pathway of virus reproduction

  1. Virus attaches to host cell and injects genetic material

  2. Virus uses host cell to produce new viral components

  3. New viruses assemble and are released, infecting more cells
• Lysogenic pathway of virus reproduction

  1. Viral genetic material incorporates into host cell's DNA

  2. Viral genes replicate with host DNA but remain dormant

  3. Trigger causes viral genes to leave host DNA and enter lytic pathway
• Sexually transmitted infections (STIs)


  Infections that are spread through sexual contact, including sexual intercourse
• HIV

  The Human Immunodeficiency Virus that kills white blood cells, leading to AIDS (Acquired Immune Deficiency Syndrome)
• Chlamydia

  A bacterial STI that can cause infertility, but doesn't always show symptoms
• Preventing the spread of STIs

  1. Using condoms during sex

  2. Screening and treating infected individuals

  3. Avoiding sexual contact
• Plant physical defences

  • Waxy cuticle on leaves and stems
  • Cell walls made of cellulose
• Plant chemical defences

  • Producing antimicrobial chemicals
  • Producing chemicals to deter pests
• Some plant chemicals can be used to treat human diseases or alleviate symptoms, e.g. quinine from cinchona tree bark and aspirin from willow trees
• Detecting plant diseases

  1. Observing symptoms in the field

  2. Analysing distribution patterns of diseased plants

  3. Laboratory testing for antigens or pathogen DNA
• Physical barriers in the human body

  • Skin
  • Hair and mucus in nose
  • Cilia and mucus in airways
  • Stomach acid
  • Lysozyme in tears
• Immune system response

  • White blood cells patrol for pathogens
  • B-lymphocytes produce antibodies specific to pathogens
  • Memory lymphocytes remember past infections
• Primary and secondary immune responses

  1. Initial slow response as body produces antibodies

  2. Memory lymphocytes enable faster, stronger secondary response

  3. Pathogen cleared before symptoms appear
• Immunisation


  • Injecting dead or inactive pathogens to trigger antibody and memory lymphocyte production
  • Provides immunity to later infection
• Pros of immunisation

  • Prevents disease outbreaks through herd immunity
  • Can virtually eliminate some diseases
• Cons of immunisation

  • Doesn't always work
  • Rare risk of adverse reactions