- Physical barriers that prevent pathogens from entering the body destroy them after they enter, or flush them out before they can establish themselves in the hospitable environment of the body’s soft tissues. The body’s most fundamental defense mechanisms are barrier defenses.
- The barrier defenses aren’t activated in reaction to infections, but they’re always working to keep a wide spectrum of pathogens at bay. The many types of barrier defences are linked to the body’s external surfaces, where pathogens may try to enter.
Skin as Barriers
- The skin is the first line of defence against microbes entering the body. Not only is the skin covered in a layer of dead, keratinized epithelium that is too dry for bacteria to grow in, but these cells also take germs and other pathogens with them as they are constantly sloughed off from the skin. Sweat and other skin secretions can also reduce pH, contain harmful lipids, and wash germs away physically.
- Another barriers is saliva, which is high in lysozyme, an enzyme that breaks down bacteria’s cell walls and kills them. The stomach’s acidic environment, which kills many bacteria, is also a barrier. Furthermore, the mucus layer of the gastrointestinal tract, respiratory system, reproductive tract, eyes, ears, and nose traps and aids the evacuation of microorganisms and detritus. Ciliated epithelial cells in the upper respiratory tract carry possibly contaminated mucus upwards to the mouth, where it is eaten and eventually ends up in the harsh acidic environment of the stomach.