Your body is equipped with a nonspecific first line of defense
against diseases and infectious invaders trying to enter it. This first line features the following.
- Skin is a physical and hostile barrier covered with oily and acidic (pH from 3 to 5) secretions from sebaceous and sweat glands, respectively.
- Antimicrobial proteins (such as lysozyme, which breaks down the cell walls of bacteria) are contained in saliva, tears, and other secretions found on mucous membranes.
- Cilia that line the lungs serve to sweep invaders out of the lungs.
- Gastric juice of the stomach, by the action of hydrochloric acid or enzymes, kills most microbes.
- Symbiotic bacteria found in the digestive tract and the vagina out compete many other organisms that could cause damage.