Fighting off pathogens
Pathogens are all around us, yet we are not sick most of the time. This is because the body has a system of defences called body defence. It works in layers, stopping pathogens from entering and destroying those that do.
First line: keeping pathogens out
The first line of defence stops pathogens before they enter the body:
- Skin — a physical barrier that blocks pathogens.
- Mucus in the nose and airways traps dust and germs.
- Tears and saliva contain substances that kill some bacteria.
- Acid in the stomach kills many pathogens in food.
Key idea
The first line of defence keeps pathogens out (skin, mucus, tears, stomach acid). The second line destroys pathogens that get inside (white blood cells).
Second line: destroying pathogens inside
If pathogens get past the first line, white blood cells in the blood fight them. Some white blood cells surround and eat the pathogens. Others make antibodies, special chemicals that stick to pathogens and destroy them.
After an infection, the body can remember a pathogen and make antibodies quickly the next time. This protection is called immunity. Vaccination gives immunity safely by training the body to make antibodies without causing the disease.
Example
When you get a cut, white blood cells rush to the wound to eat any bacteria that enter, which is why a small cut usually heals without making you ill.
Remember
- First line: skin, mucus, tears, stomach acid.
- Second line: white blood cells and antibodies.
- Vaccination gives immunity without causing disease.