C10: diseases & immunity

• pathogen: a disease-causing organism
• transmissible disease in which a pathogen can be passed from one host to another
• a pathogen is transmitted by:

  • direct contact - through blood, body fluids (HIV, hepatitis B & C, gonorrhoea)
  • indirectly - from contaminated surfaces (athletes foot, salmonella), food/water (cholera, typhoid), droplets in air (common cold, influenza), insect bites (dengue fever, malaria)
• skin: physical barrier to prevent pathogens from entering the body.

  if wounded, it immediately starts healing by forming a scab
• hair in the nose: natural filter to prevent entry of pathogens into the lungs
• mucus: traps pathogens before they can enter lungs
• stomach acid: contain hydrochloric acid which can kill pathogens
• white blood cells: defend the body against infections by phagocytosis (phagocytes) and antibody production (lymphocytes)
• control spread of disease

  • clean water supply
  • hygienic food preparation
  • good personal hygiene
  • waste disposal
  • sewage treatment
• active immunity gained :

  • after an infection by a pathogen
  • vaccination
• process of vaccination

  • weakened pathogens or their antigens put into the body
  • antigens stimulate an immune response by lymphocytes which causes them to produce antibodies
  • memory cells are produced to give long-term immunity
• role of vaccination - breaks the pathogen's chain of infection when majority of a population is vaccinated. the pathogen will have fewer places to breed and will be unable to pass from person to person. thus, prevents spread of disease (aka herd immunity)
• passive immunity: short-term defense against a pathogen by antibodies from another individual
• active immunity: long-lasting defense against a pathogen by antibody production in the body
• passive immunity gained:

  • from across the placenta
  • breastfeeding