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Quiz yourself on Human Defense Systems - Non-specificGet your flashcardsBuild my revision planTrack my progressFirst Line of Defence: Physical Barriers
Skin — The Main Barrier
Your skin is the most important physical defence against pathogens. It covers the entire body surface and prevents pathogens from entering:
- Physical barrier: Intact skin blocks pathogen entry through its tough outer layer
- Skin oils: Glands in the skin produce oils that help maintain the barrier and create an environment that is hostile to many microorganisms
- Continuous renewal: Skin cells are constantly replaced, shedding pathogens that may have landed on the surface
Mucus and Cilia — Respiratory Protection
Your respiratory system has specialised defences against airborne pathogens:
- Mucus traps: Sticky mucus in the nose and airways traps dust, pathogens, and particles before they can reach the lungs
- Cilia sweep: Tiny hair-like cilia beat rhythmically to sweep trapped pathogens upward towards the throat, where they are swallowed
Blood Clots — Sealing Wounds
When skin is broken, pathogens can potentially enter. The body responds by forming a blood clot:
- Clotting process: Platelets and clotting proteins in the blood rapidly seal the wound
- Scab formation: A scab forms over the wound, acting as a replacement physical barrier
- Prevents entry: The clot stops pathogens from entering through the damaged area
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