First line of defence – non-specific barriers
These are a combination of physical and chemical barriers that prevent all types of foreign agents from penetrating the outer layer of the body. No specific foreign agent is targeted at this level.
The barriers are:
The skin – provides an impervious barrier to pathogens.
Mucous membranes – line the entrances to the body such as in the respiratory tract entrances. Mucus produced by these membranes traps foreign particles and directs them out of the body.
Hairs and cilia – (nasal hairs) trap dust and dirt; (microscopic cilia) line some mucous membranes and direct foreign particles out of the body.
Gastric juice, vaginal secretions and urine – acidic fluids that have a protective function.
Tears, sweat and saliva – body fluids which possess some anti-bacterial properties.
Cerumen (ear wax) – produced in the ear canal and protects the canal by trapping dirt and dust particles.
A diagram of a female body showing a list of human barriers and defences against infection.
- Ear – cerumen inhibits bacterial growth
- Eyes – cleansed by tears which also contain chemical inhibiting bacterial growth
- Nasal cavity – hairs and mucus trap microorganisms
- Mouth cavity – mucous membrane traps microorganisms and the mouth is cleaned by saliva
- Skin – an impervious barrier
- Trachea and bronchi – mucous layer traps microorganisms
- Stomach – acidic juices kill many microorganisms
- Urethra – urine flow prevents bacterial growth
- Anus – mucous membrane traps microorganisms
- Vagina – acidic secretion inhibits growth of pathogens.