First Line of Defense: Barriers
Part of Human Defense Systems - Non-specific — GCSE Biology
This deep dive covers First Line of Defense: Barriers within Human Defense Systems - Non-specific for GCSE Biology. Physical and chemical barriers, white blood cell responses, inflammatory response It is section 3 of 18 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 3 of 18
Practice
19 questions
Recall
22 flashcards
First Line of Defense: Barriers
Physical Barriers
Skin - The Ultimate Barrier
Your skin is your most important defense against pathogens. This remarkable organ covers your entire body surface and provides multiple protective mechanisms:
- Physical barrier: Intact skin prevents pathogen entry through its tough, keratinized outer layer
- Sebum production: Sebaceous glands produce oily sebum that creates an acidic environment (pH 5.5) on skin surface
- Antimicrobial properties: Sebum contains antimicrobial compounds that kill bacteria and fungi
- Continuous renewal: Skin cells are constantly replaced, shedding pathogens that might have attached
Mucus and Cilia - Respiratory Protection
Your respiratory system has specialized defenses against airborne pathogens:
- Mucus traps: Sticky mucus in nasal passages and airways traps dust, pathogens, and particles
- Ciliary escalator: Tiny hair-like cilia beat rhythmically (1000 times per minute) to sweep trapped pathogens upward
- Antimicrobial mucus: Contains lysozyme and other antimicrobial substances
- Cough and sneeze reflexes: Forceful expulsion of trapped pathogens
Chemical Barriers
Stomach Acid - The Acid Bath
Your stomach produces powerful hydrochloric acid that creates an extremely hostile environment for pathogens:
- Low pH: Stomach acid has pH 1-2, killing most bacteria and viruses
- Protein denaturation: Acid denatures pathogen proteins and enzymes
- Continuous production: About 2-3 liters of gastric juice produced daily
- Protective mucus: Stomach lining protected by alkaline mucus barrier
Lysozyme - The Universal Antibiotic
Lysozyme is a powerful antimicrobial enzyme found throughout your body:
- Locations: Tears, saliva, mucus, and other body secretions
- Mechanism: Breaks down peptidoglycan in bacterial cell walls
- Effectiveness: Particularly effective against Gram-positive bacteria
- Constant protection: Provides continuous antimicrobial activity
Other Chemical Defenses
- Saliva: Contains lysozyme, immunoglobulin A, and lactoferrin
- Sweat: Contains salt and antimicrobial peptides
- Ear wax: Acidic and contains antimicrobial substances
- Vaginal secretions: Acidic pH maintained by beneficial bacteria