At its most general level, inflammation is a reaction to any traumatic event in the tissues that attempts to restore homeostasis: It is a normal and necessary process that helps to clear away invading microbes and cellular debris left by immune reactions. Most people manifest inflammation in some way every day. It appears in the flare of a cut, the blistering of a burn, the painful lesion of an infection, and the symptoms of allergy, and at times it can even go unnoticed.
Inflammation is readily identifiable by a classic series of signs and symptoms characterized succinctly by four Latin terms: rubor, calor, tumor, and dolor. Rubor (redness) is caused by increased circulation and vasodilation in the injured tissues; calor (warmth) is the heat given off by the increased flow of blood; tumor (swelling) is caused by increased extracelluar fluid accumulating in the tissues; and dolor (pain) is caused by the stimulation of nerve endings from the pressure of swelling or by chemical mediators (figure 1). A fifth symptom, loss of function, is sometimes added for a complete picture of effects that can accompany inflammation. Although these manifestations are often unpleasant, they serve an important warning that injury has taken place and will set in motion responses that can save the body from further injury.
Fig1. The response to inflammations. The classic indicators of inflammation, whether due to infection or injury, are rubor (redness), calor (warmth), tumor (swelling), and dolor (pain). Each of the events is an indicator of one of the mechanisms of inflammation described in this section. Robert Kirk/Getty Images
Factors that can elicit an inflammatory response include trauma from infection (the primary emphasis here), tissue injury or death, and specific immune reactions. Although the details of inflammation are very complex, its chief functions can be summarized as follows:
1. to mobilize and attract immune cells and chemicals to the site of the injury,
2. to set in motion mechanisms to repair tissue damage and localize and clear away harmful substances, and
3. to destroy and block microbes from further invasion (see process figure 2).
Process Figure 2 The major events in inflammation.
The inflammatory response is a powerful defensive reaction, a means for the body to maintain stability and restore itself after an injury. But when it is chronic, it has the potential to actually cause tissue injury, destruction, and disease.
