There are three lines of defense in a human body before a pathogen can successfully enter the human body and infect it.
Mechanical barriers
- Our skin is a mechanical barrier. It serves to physically block pathogens from entering the body.
- Mucous membrane serves as the mechanical barrier at body openings. It secretes mucus to trap pathogens. Its cilia sweeps off mucus and pathogens towards the body openings to eject them out.
Chemical barriers
- These barriers destroy pathogens found on the outer body surface, body opening, and on inner body lining.
- There are enzymes that kill off pathogen. They are found in sweat, tears, mucus, and saliva.
Urine, semen, and stomach acid contains certain components that kills off pathogens.
Biological barriers
- There are good bacteria in our body. They use up food and space in our body to make sure that harmful bacteria can't grow.
