3.1.6 Human Defence Systems

The non-specific defence system works to prevent pathogens from entering the body.

1. The skin

• Acts as a physical barrier
• It produces antimicrobial secretions to kill pathogens
• Good microorganisms known as skin flora compete with the bad microorganisms for space and nutrients

2. The nose

• Has hairs and mucus (sticky substance) which prevent particles from entering your lungs

3. The trachea and bronchi

• Secrete mucus in order to trap pathogens
• Cilia (hair-like structures on cells) beat to waft mucus upwards so it can be swallowed

4. The stomach

• Produces hydrochloric acid that kills any pathogens in your mucus, or food and drink

Mode of action	How it protects you
Phagocytosis (engulfing\ and consuming pathogens)	This destroys them, meaning they can no longer make you feel ill.
Producing antibodies	Each pathogen has an antigen on their surface, which is a structure which a specific complementary antibody can bind to. Once antibodies begin to bind to the pathogen, the pathogens start to clump together, resulting in it being easier for white blood cells to find them. If you become infected again with the same pathogen, the specific complementary antibodies will be produced at a faster rate. The individual will not feel the symptoms of the illness. They are said to be immune.
Producing antitoxins	They neutralise the toxins released by the pathogen by binding to them