Biology - Lines of Defence
Lines of Defence
There are three lines of defence:
The skin is a physical barrier; the linings of the respiratory tract,
digestive and urinary systems produce chemicals which wash, inhibit or
destroy pathogens; for example, sebum (oil), tears, mucus and digestive
If pathogens/parasites enter, white cells of various kinds act.
* phagocytes  (neutrophils) carry out phagocytosis
* eosinophils produce anti-parasitic toxins
* basophils promote an inflammatory response to presence of parasites
* serum proteins stick to bacteria and fungi or may damage bacterial
* interferons  are secreted by some cells when they are infected by
View the video of a macrophage: a white cell that engulfs and destroys
invading microbes and other foreign material.
Involves specialised lymphocytes  producing B cells (humoral immunity)
and T cells (cell-mediated immunity).
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