Non-specific response to infection

Biology Unit 4

Non-specific response to infection

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Biology Unit 4
Revision Notes
Topic 6: Infection, Immunity and Forensics
12. Describe the non-specific responses of the body to
infection, including inflammation, lysozyme action,
interferon and phagocytosis.
Respons Inflammation Lysozyme action Interferon Phagocytosis
How it Damaged white cells An enzyme found A chemical White blood cells
fights release histamines that in tears, sweat released from engulf, digest and
the cause arterioles to dilate and the nose cells stops destroy bacteria and
infectio and capillaries to become destroys bacteria protein foreign material. These
n more permeable. Blood by breaking synthesis in phagocytes include
flow to the area increases down the viruses neutrophils and
and plasma, white blood bacterial cell monocytes (which
cells and antibodies leak walls become macrophages)
out into tissues
The inflammatory response involves a number of stages:
Special cells called mast cells are found in the connective tissue below the skin and around
blood vessels. When this tissue is damaged, mast cells along with damaged white blood cells
release chemicals called histamines.
They cause the blood vessels in the area, particularly the arterioles, to dilate, causing local
heat and redness. The locally raised temperature reduces the effectiveness of pathogen
reproduction in the area.
The histamines also make the walls of the capillaries leaky as the cells forming the walls
separate slightly. As a result fluid, including plasma, white blood cells and antibodies, is
forced out of the capillaries causing swelling (oedema) and often pain.
The white blood cells and antibodies disable and destroy the pathogens.
Normal body temperature is maintained by the hypothalamus and follows a regular circadian rhythm,
lowest in the early hours of the morning and highest at about 10pm. When a pathogen infects the
body it causes the hypothalamus to reset to a higher body temperature ­ we have a fever.
A raised temperature seems to help the body combat infection in two ways:
Many pathogens reproduce most quickly at 37°C or lower. Thus a raised temperature will
reduce the ability of many pathogens to reproduce effectively and so they cause less
Your specific response system works better at higher temperatures and so will be more
successful at combating the infection.
Text Book: p.96 ­ 98

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Biology Unit 4
Revision Notes
In a bacterial infection the temperature rises steadily and remains fairly high until treatment is
successful or the body overcomes the infection. In a viral infection the temperature tends to
"spike", shooting up high every time viruses burst out of the cells and then dropping down to normal
If fevers get too high they can be damaging and even fatal.…read more


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