Chapter 6

• Immunity


  The body's defence mechanisms to protect itself against the entry of microorganisms
• Immune system


  A complex network of organs, cells and proteins that defends the body against infection, whilst protecting the body's own cells
• The immune system keeps a record of every germ (microbe) it has ever defeated so it can recognise and destroy the microbe quickly if it enters the body again
• Microorganism


  Living organisms too small to be seen with the naked eye; they are microscopic
• Pathogen


  A harmful microbe or an agent that causes an infectious disease
• Groups of pathogens


  • Viruses (not living organisms)
  • Bacteria
  • Fungi
  • Protists
• Not all species within these groups (apart from the viruses) are pathogens, as many bacteria, fungi and protists are harmless and do not cause disease
• All viruses are pathogenic as they can only exist by living inside the living cells of other organisms (or by using these cells to create more viruses)
• Disease


  A disorder which affects an organism, with a specific cause and recognizable signs and symptoms
• Differences between transmissible and non-transmissible diseases

  • Transmissible disease: Communicable diseases caused by microorganisms that can spread from one person/organism to another
  • Non-transmissible disease: Not transferred between people or other organisms, not caused by pathogens, long-lasting effects
• Transmissible diseases


  • Tuberculosis (bacterial)
  • HIV (viral)
  • Athlete's foot (fungal)
• Non-transmissible diseases


  • Asthma
  • Coronary heart disease
  • Most cancers
• Nutritional disease


  Related to the absence of certain nutrients in the diet, e.g. kwashiorkor, marasmus, scurvy, rickets
• Degenerative disease


  Degeneration of body tissues over time, e.g. osteoarthritis, osteoporosis, Alzheimer's, long-sightedness, Parkinson's
• Hereditary disease


  Disorder caused by mutations in genes or chromosomes passed down from parent to child, e.g. cystic fibrosis, Down syndrome, albinism
• Other examples of non-communicable diseases

  • Cancer
  • Diabetes mellitus
  • Stroke
  • COPD
  • Coronary heart disease
  • Neurological disorders
• Infectious disease


  A communicable disease caused by another living organism, such as viruses, bacteria, or fungi
• Infectious diseases


  • Tuberculosis (bacterial)
  • HIV (viral)
  • Athlete's foot (fungal)
• Transmission of communicable diseases

  • Direct contact with blood or body fluids
  • Indirect contact through air, water, contaminated surfaces/foods
  • Vector-borne transmission (e.g. malaria spread by mosquitoes)
• Viruses


  • Small particles, parasitic, can only reproduce inside living cells, infect all types of living organisms, have a protein coat and contain DNA or RNA but no cellular structure
• Capsomeres


  Small units that make up the protein coat of a virus
• Antigens


  Proteins and other substances projecting from cell membranes that are specific to that type of cell
• Allergy


  A condition where the body becomes extremely sensitive to a particular substance (allergen) that produces characteristic symptoms
• Allergens


  • Pollen
  • Dust mites
  • Pet dander
• Innate immunity


  The defence system you are born with, including physical and chemical barriers that prevent pathogens from entering the body
• Adaptive immunity


  Immunity that develops when the immune system responds to a foreign substance or microorganism
• Phagocytes


  White blood cells that recognize and engulf pathogens through phagocytosis
• Mucus clearance


  Waft the mucus up to the back of the throat where it is swallowed
• The stomach produces acid, and this destroys the microorganisms in the mucus you swallow as well as the majority of the pathogens you take in through your mouth in your food and drink
• Both the digestive and respiratory systems have good defences to help prevent pathogens constantly causing infections
• Phagocytes


  White blood cells that are produced continuously in the bone marrow and are responsible for invasive microorganisms
• Phagocytosis


  The process of recognising and engulfing a pathogen
• Adaptive immunity


  A type of immunity that develops when a person's immune system responds to a foreign viral substance or microorganism
• Some pathogens still get inside your body despite your body's defence mechanisms
• Lymphocytes


  A type of white blood cell that recognise proteins on the surface of pathogens called antigens
• Antibody production


  Lymphocytes detect foreign antigens and produce antibodies which are complementary in shape to the antigen
• An antibody will only work on one type of microorganism because of its complementary nature
• Antibody action


  Antibodies immobilise microorganisms by clumping them together, reducing symptoms and preventing the spread of infection
• Phagocytosis


  A phagocyte (white blood cell) engulfs and digests the clumped microorganisms
• This process can take a few days, during which time you may feel ill