Final answer:
A secondary barrier is an additional line of defense that pathogens must overcome after the primary barrier. Examples of secondary barriers include saliva, stomach acid, mucus layer, and ciliated epithelial cells.
Step-by-step explanation:
A secondary barrier refers to the additional line of defense that pathogens must overcome after the primary barrier. While the primary barrier is the skin, secondary barriers include other physical and chemical barriers that prevent pathogens from entering the body or destroy them after they enter. Examples of secondary barriers include saliva, stomach acid, the mucus layer in various parts of the body, and the ciliated epithelial cells in the respiratory tract. These secondary barriers work in conjunction with the primary barrier to protect the body from a wide range of pathogens.