AQA GCSE Human defences against pathogens (Biology)
Human defences against pathogens
Our primary defences try to stop pathogens entering the body, these are all non specific defences.
Non-specific defence mechanisms are the body’s general, immediate defences that work against any pathogen, not just one specific type.
Non specific defences include
1. Skin
2. Nose
3. Trachea and bronchi
4. Stomach.
| Part of body | How it protects us |
|---|---|
| Skin | Skin forms a protective barrier to stop pathogens from entering. If the skin is cut, the blood clots and dries to form a scab, sealing the wound and preventing pathogens from entering. The skin contains glands that secrete oils and sweat which contain antimicrobial chemicals. These chemicals will kill pathogens. |
| Nose | Nose contains both mucus and hairs which traps pathogens. |
| Trachea and Bronchi | Both trachea and bronchi contain goblet cells that secrete a sticky mucus and ciliated cells with cilia. The mucus traps dust and pathogens, whilst the cilia hairs waft the mucus and pathogens up to the top of the airways. Swallowing then takes the mucus and pathogens down the oesophagus into the stomach. Acid in the stomach will kill the pathogens. See the diagram below |
| Stomach | The stomach contains hydrochloric acid, which kills pathogens on food. |
Below is an image of the airways showing goblet cells, ciliated cells and mucus.
Role of the immune system.
Our immune system forms part of our secondary defences. Secondary defences deal with pathogens once they have entered the body.
Once the pathogen has entered the body, the immune system will try to destroy it.
White blood cells form part of our immune system to protect us against pathogens.
There are three main processes that the immune system uses to kill pathogens:
1.Phagocytosis
2. Antibody production
3.Antitoxin production
Phagocytosis
The phagocyte will engulf the pathogen (bacterium in this case) and then use enzymes to break it down.
Antibody production
Lymphocyte will produce antibodies which bind to the antigens on the pathogen (bacterium in this case). The antibodies will destroy the pathogen.
The shape of the antibodies is complementary to that of the antigens.
(Don’t get antibody and antigen mixed up)
Antibody is like your bodies bodyguard.
Antigen sounds like ANTAGonist (the “enemy”).
Antitoxin production
Lymphocyte will produce antitoxins which bind to toxins produced by the bacterium. The antitoxins will neutralise the toxins, so they cannot harm us.
Practice Questions
1.Define the term non specific defence
2. Give one example of a non specific defence that protects us against pathogens.
3. Describe how phagocytes protect us against pathogens.