Protective functions of inflammation and acute–chronic progression
THE CONTEXT
Inflammation brings circulating host defenses into vascularized tissues affected by infection or injury, allowing elimination of harmful agents and initiation of repair.
Purpose and host defenses
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Inflammation is a protective response essential for survival. It removes the initial causes of injury, such as microbes and toxins, as well as necrotic cells and tissues, and initiates tissue repair.
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Defensive mediators include phagocytic leukocytes, antibodies, and complement proteins.
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Most of these defenses normally circulate in blood, whereas infections and dead cells are typically located outside vessels in tissues. Inflammation delivers leukocytes and proteins to these sites and activates them to remove harmful substances.
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Without inflammation, infections would remain unchecked, wounds would not heal, and injured tissues could remain persistent sores.
Acute inflammation
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Acute inflammation is the initial rapid response to infection and tissue damage. It develops within minutes to hours and lasts from several hours to a few days.
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Its main features are leakage of fluid and plasma proteins, producing edema, and accumulation of leukocytes, predominantly neutrophils, also called polymorphonuclear leukocytes.
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When the offending stimulus is eliminated, the acute reaction quickly subsides.
Progression to chronic inflammation
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Failure to clear the stimulus can lead to a prolonged phase called chronic inflammation.
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Chronic inflammation is associated with continuing tissue destruction and fibrosis, meaning deposition of connective tissue.