Physical & Chemical Barriers to Microbial Invasion: A Comprehensive Overview

Physical Barriers

• Skin: Largest organ; multi-layered, produces antimicrobial substances, secretes fatty acids inhibiting microbes.
• Mucous membranes: Line respiratory, digestive, urogenital tracts; produce mucus trapping microbes.
• Saliva: Contains lysozyme, lactoferrin—antimicrobial.
• Stomach acid: pH ~1.5 kills/inhibits most microorganisms.
• Intestinal flora: Beneficial bacteria compete with pathogens, produce antimicrobials.

Chemical Barriers

• Antimicrobial peptides: Small proteins killing/inhibiting microbes.
• Cytokines: Immune signaling proteins regulating response, activating peptides/cells.
• Complement system: Protein cascade killing microbes, activated by foreign molecules.