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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
juices.

If pathogens/parasites enter, white cells of various kinds act.

* phagocytes [1] (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
membranes

* interferons [2] are secreted by some cells when they are infected by
virus particles.

View the video of a macrophage: a white cell that engulfs and destroys
invading microbes and other foreign material.

Involves specialised lymphocytes [3] producing B cells (humoral immunity)
and T cells (cell-mediated immunity).

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Links:
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[1] http://alison.com/#
[2] http://alison.com/#
[3] http://alison.com/#