Disease and Immunity: Disease

Pathogens Cause Infectious Diseases

• pathogen: any organism that causes disease
• includes microorganisms and larger organisms e.g. tapeworms
• includes bacteria, fungi and all viruses

Pathogens can Penetrate an Organism's Interface with the Environment

• enter the body through the organism's surface of contact/interface with the environment
• 3 main interfaces:
  • gas-exchange system
    • breathe in air containing pathogens
    • most trapped by mucus
    • cilia beat and move mucus to remove it
    • some reach alveoli, invade cells and cause damage
  • skin
    • damage to the skin can allow pathogens on the surface to enter the bloodstream
    • blood clots to prevent this
    • some may get in before the blood clots
  • digestive system
    • eat and drink food containing pathogens
    • most killed by acidic conditions in stomach
    • some may survive
    • invade the cells of the gut wall

Pathogens Cause Disease by Producing Toxins and Damaging Cells

• despite protective mechanisms pathogens can successfully enter the body
• they cause disease in two main ways:
  • production of toxins
    • many bacteria release toxins
      • e.g the bacterium that causes tetanus produces a…