Defence Against Pathogens
Human Biology (Year 12)
What are protective reflexes?
Protective reflexes help to protect the body from injury, including the blink reflex, or from infection, such as vomiting, and four reflexes help to protecting against infection.
How do protective reflexes work?
There are four main protective reflexes which you need to be aware of. These include sneezing, coughing, vomiting and diarrhoea.
The stimulus for sneezing is irritation of the walls of the nasal cavity which may be caused by noxious fumes or dust particles, which are likely to be carrying microorganisms. Forceful expulsion of air from the lungs carries mucous, foreign particles and irritating gases out through the nose and mouth.
The stimulus is irritation in the lower respiratory tract (the bronchi and bronchioles) where air is forced from the lungs to try remove the irritant.
The stimulus for vomiting is psychological stimuli, excessive stretching of the stomach and bacterial toxins. Contractions of the muscles of the abdomen and the diaphragm expels the stomach contents.
Can occur when irritation of the small and large intestines by bacteria, viruses or protozoans occurs, and is stimulated by increased contractions of the muscles of the wall of the intestine so that the irritant is removed as quickly as possible.
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