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First Line of Defense
The immune system has 3 lines of defense in response to pathogen exposure.
The first line of defense is physical and chemical barriers that are classified as innate immunity nonspecific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body. . These physical and chemical barriers attack the pathogen upon exposure. Examples of the barriers:
- Physical barriers
- Skin - has thick layer of dead cells in the epidermis which provides a physical barrier. Periodic shedding of the epidermis removes microbes.
- Mucous membranes - produce mucus that trap microbes.
- Hair - within the nose filters air containing microbes, dust, pollutants.
- Cilia - lining the upper respiratory tract traps and propels inhaled debris.
- Urine - flushes microbes out of the urethra tube extending from bladder to outside environment .
- Defecation and vomiting - expels microorganisms.
- Chemical Barriers
- Lysozyme - enzyme produced in tears, perspiration, and saliva that can break down cell walls and thus acts as an antibiotic (kills bacteria).
Image 3: Tears as a Chemical Barrier
- Gastric juice - in the stomach destroys bacteria and most toxins because it is highly acidic (pH 2-3).
- Acidity on skin - inhibits bacterial growth.
- Sebum - provides a protective film on the skin and inhibits growth.
- Lysozyme - enzyme produced in tears, perspiration, and saliva that can break down cell walls and thus acts as an antibiotic (kills bacteria).
Check for understanding:
-The first line of defense involves ________ and _______ barriers of the innate immune system.
-Cilia lining the respiratory system, vomiting to expel pathogens, and urine to flush out pathogens are all a part of the _______ barriers of the 1st line of defense.
-Why is saliva considered a chemical barrier in the first line of defense?
