Health and disease

• Health


  A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity
• Aspects of health


  • Physical
  • Mental
  • Social
• Communicable disease


  Diseases that can be transferred between individuals
• Non-communicable disease


  Diseases that cannot be transferred between individuals
• Communicable diseases can be spread through air particles from coughing, from parasites in faeces, or through bodily fluids including blood, semen and breast milk
• Non-communicable diseases usually have a genetic component or are acquired due to lifestyle factors
• The presence of one disease can lead to increased susceptibility to other diseases
• Pathogen


  An organism which causes disease
• Types of pathogens


  • Viruses
  • Bacteria
  • Fungi
  • Protists
• Viruses


  • Very small
  • They move into cells and use the biochemistry to make many copies of itself
  • This leads to the cell bursting and releasing all of the copies into the bloodstream
  • The damage and the destruction of the cells makes the individual feel ill
• Bacteria


  • Small
  • They multiply very quickly through dividing by a process called binary fission
  • They produce toxins that can damage cells
• Fungi


  • They can either be single celled or have a body made of hyphae (thread-like structures)
  • They can produce spores which can be spread to other organisms
• Protists


  • Some are parasitic, meaning they use humans and animals as their hosts (live on and inside, causing damage)
• Common infections and their pathogens

  • Cholera (Vibrio cholerae)
  • Tuberculosis (Mycobacterium tuberculosis)
  • Chalara ash dieback (Hymenoscyphus fraxineus)
  • Malaria (Plasmodium falciparum)
  • HIV (Human Immunodeficiency Virus)
  • Helicobacter (Helicobacter pylori)
  • Ebola (B. ebolavirus)
• Ways pathogens are spread


  • Direct contact
  • By water
  • By air
• Reducing the spread of pathogens

  • Improving hygiene
  • Reducing contact with infected individuals
  • Removing vectors
  • Vaccination
• Sexually transmitted infections (STIs)

  Infections which can be spread through sexual contact, including oral and vaginal sex
• Examples of STIs


  • Chlamydia
  • HIV
• Plant barriers against disease

  • Physical barriers: Thick cellulose cell wall, thick waxy cuticle, layer of bark, closing of stomata
  • Chemical barriers: Antimicrobial chemicals, proteins and enzymes, compounds that attract larger insects to feed on pests
• Identifying plant disease in the lab

  1. Cuttings taken from diseased plant

  2. Virus/bacterium grown on culture medium/agar plate

  3. Pathogen tested and identified using monoclonal antibody testing kit (ELISA kit)
• Human physical barriers against disease

  • Mucus
  • Cilia
  • Skin
• Human chemical barriers against disease


  • Lysozymes
  • Hydrochloric acid
• Phagocytosis


  White blood cells engulfing and consuming pathogens, destroying them so they can no longer make you feel ill
• Mucus


  Produced by goblet cells in the airway, traps bacteria and other pathogens before they reach the lungs and cause infection
• Goblet cells in the airway


  • Produce mucus
• Cilia


  • Ciliated epithelial cells (have cilia on their surface)
  • Wafts away mucus that has trapped pathogens, to be killed by stomach acid
• Chemical barriers


  Protect against pathogens
• Skin


  • Skin cells
  • Provides a physical barrier against pathogens, protecting the tissues and cells beneath it from infection
• Lysozymes


  Used by white blood cells to kill and digest bacteria
• Hydrochloric acid


  Used to kill bacteria in food reaching the stomach - to prevent infection
• Phagocytosis


  1. White blood cells engulfing and consuming pathogens

  2. Destroys them, meaning they can no longer make you feel ill
• Producing antibodies


  1. Each pathogen has an antigen on their surface, which is a structure which a specific complementary antibody can bind to

  2. Once antibodies begin to bind to the pathogen, the pathogens start to clump together, resulting in it being easier for white blood cells to find them and engulf them in phagocytosis

  3. During this process, the antigens also trigger production of memory lymphocytes (lymphocytes are a special type of white blood cell)

  4. If you become infected again with the same pathogen, the specific complementary antibodies will be produced at a faster rate

  5. The individual will not feel the symptoms of the illness. They are said to be immune
• Producing antitoxins


  They neutralise the toxins released by the pathogen by binding to them
• Vaccination


  • Involves making an individual immune to a certain disease- they are protected against it before they have been infected
  • By immunising a large proportion of the population, the spread of the pathogen is reduced as there are less people to catch the disease from (called herd immunity)
• Naturally


  • When you are infected with a pathogen, you feel ill until white blood cells manufacture the correct specific antibody to combat it
  • Upon a secondary infection, the antibodies can be produced much quicker, so the pathogen can be destroyed and the symptoms are not felt
  • Vaccinations replicate the first infection so that when the person is exposed to the real disease they do not feel any symptoms, just like in a secondary infection
• Vaccine


  • Contains a dead or inactivated form of the pathogen
  • This stimulates white blood cells to produce antibodies complementary to the antigens on the pathogen
• Antibiotics


  • Can only be used to treat bacterial infections, and not those caused by viruses, fungi or other pathogens
  • Bacteria are susceptible to antibiotics because antibiotics inhibit cell processes in the bacterium
  • Viruses and other pathogens often use cell machinery in host cells to reproduce, and these are unaffected by antibiotics
• Advantages of vaccination

  • They have eradicated many diseases so far (e.g smallpox) and reduced the occurrence of many (e.g rubella)
  • Epidemics (lots of cases in an area) can be prevented through herd immunity
• Disadvantages of vaccination


  • They are not always effective in providing immunity
  • Bad reactions (such as fevers) can occur in response to vaccines (although very rare)
• Nutrient broth solution


  Involves making a suspension of bacteria to be grown and mixing with sterile nutrient broth (the culture medium), stoppering the flask with cotton wool to prevent air from contaminating it and shaking regularly to provide oxygen for the growing bacteria