Human Body Defence Systems against Pathogens
Pathogens are disease causing micro-organisms. Disease can cause infection through various mechanisms.
Air e.g. viruses such as a cold.
Skin e.g. bacteria such as syphilis.
Body fluids e.g. AIDS virus.
Food e.g. Salmonella in spoilt food.
1. Skin: This is a barrier to keep out pathogens.
2. Chemical: Enzymes in saliva and stomach acid kills most pathogens.
3. Phagocytes: White blood cells surround and digest pathogens.
4. Lymphocytes:The lymphocytes (white blood cells) detect pathogens by noticing a chemical sign called an
antigen. When this is detected an antibody is released. The antibody destroys the pathogen.
Natural immunity occurs when you are first affected by a disease causing micro-organism. The body, builds up antibodies to the pathogen, which then destroy the pathogen. If you are again infected by the same pathogen the body is able to remember and destroy the pathogen. This is natural immunity.
Artificial immunity is provided to the body through a vaccination. Dead or weakened forms of the pathogen are introduced to the body. Lymphocytes produce an antibody which can destroy the pathogen. If a person is then infected by the pathogen the body is able to produce the antibody which will destroy the pathogen.