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BARRIERS TO PATHOGEN ENTRY

BARRIERS TO PATHOGEN ENTRY

Pathogens enter through areas not covered by skin – nose, mouth, eyes, gas exchange surfaces, gastrointestinal tract and genital tract and through wounds.

  • Eyes, nose, mouth: Tears contain the enzyme lysozyme which helps to digest microbes – breaks down bateria cell walls
  • Skin: A tough, physical barrier containing keratin which is strong and impermeable – hard to penetrate
  • Skin flora: The skin has its own microbes which out-compete pathogens – reduce colonisation by other bacteria. Sebum is an oily fluid made by the skin and can also kill microbes
  • Earwax: Bacteriocidal
  • Respiratory tract: Contain mucus and cilia which traps bacteria, preventing the entry of pathogens into the lungs – transported up the trachea to be swallowed into the stomach
  • Vaginal secretions: Acidic
  • Stomach: Contains hydrochloric acid which protects against microbes and kills bacteria – the low pH denatures enzymes of most pathogens
  • Blood clotting: Seals wounds to prevent entry of pathogens
  • Intestines: Harmless bacteria out-compete pathogens

 

DEFENCE MECHANISMS:

Non specific:

  • Do not distinguish between pathogens but respond to all in the same way
  • Act immediately as a barrier or through phagocytosis

Specific:

  • Distinguish between different pathogens
  • Less rapid but long lasting
  • Involve lymphocytes – cell-mediated (T cells) or humoral (B cells)