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Quiz yourself on Human Defense Systems - Non-specificGet your flashcardsBuild my revision planTrack my progressWhy Physical and Chemical Barriers Are the First Priority
Non-specific defences work on a simple but powerful principle: it is far cheaper (in energy and resources) to prevent pathogen entry than to fight an established infection. The skin, mucus, and stomach acid collectively block the vast majority of potential pathogens before they ever reach internal tissues.
The skin works because pathogens need to penetrate a multi-layered barrier. When pathogens enter the respiratory tract, mucus acts like flypaper — its sticky glycoprotein chains physically trap airborne particles. The cilia then act like a conveyor belt, beating in coordinated waves to sweep mucus (with its trapped cargo) upward to the throat, where it is swallowed and destroyed by stomach acid.
Stomach acid (pH ~2) is one of the harshest environments in the body. This extremely low pH denatures bacterial proteins, destroys viral coats, and kills most pathogens before they can infect gut tissue.
The key insight for exam purposes: these barriers are non-specific because they do not need to recognise any particular pathogen. They work the same way on every type of invader, which makes them extremely efficient as a first line of defence.
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