Physical barrier to microbial penetration Sloughing of outer layers removes attached bacteria Provide dry, acidic, and cool conditions that limit bacterial growth Production of acids, alcohols, and toxic lipids that limit bacterial growth
Flushing action of tears removes microorganisms Tears contain lysozyme that destroys bacterial cell wall Mediate specific and nonspecific protection mechanisms against microorganisms that penetrate outer tissue layers and moist environment in which many microbial agents thrive.
The follicles and glands of the skin produce various natural antibacterial substances. However, many microorganisms can survive the conditions of the skin. These bacteria are known as skin colonizers, and they often produce substances that may be toxic and inhibit the growth of more harmful microbial agents. Beneath the outer layers of skin are various host cells that protect against organisms that breach the surface barriers. These cells, collectively known as skin-associated lymphoid tissue, mediate specific and nonspecific responses directed at controlling microbial invaders.
Because cells that line the respiratory tract, gastrointestinal tract, and genitourinary tract are involved in numerous functions besides protection, they are not covered with a hardened acellular layer like that
BOX 3-2 Protective Characteristics of Mucous Membranes
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