Anatomical Barriers
| Anatomical barrier | Additional defense mechanisms |
|---|---|
| Skin | Sweat, desquamation, flushing, organic acids |
| Gastrointestinal tract | Peristalsis, gastric acid, bile acids, digestive enzyme, flushing, thiocyanate, defensins, gut flora |
| Respiratory airways and lungs | Mucociliary elevator, surfactant, defensins |
| Nasopharynx | Mucus, saliva, lysozyme |
| Eyes | Tears |
The epithelial surfaces form a physical barrier that is very impermeable to most infectious agents, acting as the first line of defense against invading organisms. Desquamation of skin epithelium also helps remove bacteria and other infectious agents that have adhered to the epithelial surfaces. In the gastrointestinal and respiratory tract, movement due to peristalsis or cilia helps remove infectious agents. Also, mucus traps infectious agents. The gut flora can prevent the colonization of pathogenic bacteria by secreting toxic substances or by competing with pathogenic bacteria for nutrients or attachment to cell surfaces. The flushing action of tears and saliva helps prevent infection of the eyes and mouth.
Read more about this topic: Innate Immune System
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