Protection Against Disease

The human body has a number of barriers that prevent pathogens from entering the body:

  • The skin
  • Sebum
  • Tears, saliva and urine
  • Mucus in respiratory tracts
  • Commensals
  • Stomach acid and enzymes

If the body is injured, a general inflammatory response will take place:

  • blood clots at the site of a cut, which seals the cut, to prevent pathogens entering the blood
  • inflammation around the site of the injury takes place
  • Macrophages are attracted to the site of injury, where they destroy pathogens by phagocytosis

There are four main types of immunity:

  • 1. Active natural immunity: memory cells develop after natural exposure to antigens
  • 2. Active artificially induced immunity: memory cells develop after vaccination
  • 3. Passive natural immunity: antibody transfer (e.g. through placenta or breast feeding) results in short-term immunity (a few months), as no memory cells develop
  • 4. Passive artificially induced immunity: antibodies are injected (short-term immunity)

 It is difficult to become immune to a virus, as they undergo many mutations, resulting in many different forms producing similar symptoms, but with different antigens

This video explains about vaccination


Antibiotics are only effective against bacterial infections

Antibiotics work in a number of ways:

  • Inhibiting cell wall synthesis
  • Binding to ribosomes and inhibiting protein synthesis
  • Interfering with prokaryotic DNA replication and transcription
  • Binding to the cell membrane to make it more permeable
  • Inhibiting cell metabolism

Bacteria may become resistant to antibiotics by altering the structure of the antibiotic or by modifying the bacterial cells.

Resistance develops as a spontaneous mutation, and can spread through the population asexually and sexually