Comes about as a result of chemical messages produced by “mediators”.
There are two major groups of mediators.
Cell Derived Mediators (produced by White Blood Cells)
Plasma Derived Mediators (found in the blood plasma)
1. Cell Derived Mediators
Arachidonic acid derivatives (Prostaglandins and Leukotrines) Also involved in blood clotting. Produced rapidly local to the site of infection. Short range of action. Degenerate spontaneously.
N.B. Corticosteroids and Aspirin reduce inflammation by inhibiting the production of prostaglandins.
Cytokines Lymphokines and Monokines
One of the most important of these is a substance known as interleukin. This stimulates lymphocytes and other white blood cells into action. Also promotes fever by resetting the body's thermostat located in the hypothalamus. In addition it induces drowsiness (somnolence).
Effects are vasodilation and increased vascular permeability. Appears to be effective in the early stages as evidenced by the fact that antihistamines have no effect upon vascular permeability 1 hour after the onset of inflammation.
Plasma Derived Mediators
An extremely important complex of over 20 proteins found in the blood plasma Increases vascular permeability. Opsonisation basically coating invading cells in order to make them more appetisin to phagocyic cells. Chemotaxis producing chemicals which attract important elements of the specific and non-specific defence mechanisms to the site of infection. Direct lysis of organisms.
These are chemical messages from virally infected cells that are borne in the plasma. They stimulate other cells to produce anti-viral proteins. Virus particles produced in cells exposed to interferon are less effective at infecting other cells. Also stimulate Natural Killer Cells into action. N.B. They are not viral specific and cannot save the infected cell. Appear to be most effective in short term viral infections such as colds and flu.
Overall effects of the inflammatory response
Blood vessels in the infected area dilate, and as a result blood flow to the area increases. This makes skin in the area look red and feel warm. Capillaries in the area become more permeable allowing fluid to seep into the surrounding tissue. As this occurs oedematous swelling around the infected site occurs. The swelling and the effects of some of the chemicals released results in pain. Hence clinical characteristics of the inflammatory response are known as redness, heat, oedema and pain.