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)