Inflammation: Introduction

Acute inflammation presents five classic signs: redness from vasodilation and increased blood flow, heat from elevated metabolism and circulation, swelling from protein-rich fluid accumulation due to increased vascular permeability, pain from mediators like prostaglandins and bradykinin stimulating nerve endings, and loss of function from combined effects of pain, swelling, and tissue damage.

Physical trauma such as fractures or lacerations damages cells and releases intracellular contents, triggering inflammation. A sprained ankle exemplifies this process: the injury damages ligaments, causing redness, swelling, and pain as the body initiates its protective inflammatory response to clear damaged tissue and begin repair.

Ischemia, or reduced blood supply, deprives tissues of oxygen and causes cell injury. If prolonged, ischemia results in tissue death called infarction, which releases danger signals that activate inflammation. This inflammatory response helps eliminate necrotic cells and initiate tissue repair processes.

Allergens like pollen, dust, mold, or animal dander trigger immune responses that cause inflammation. When allergens bind to IgE on mast cells, histamine is released, inflaming tissues such as nasal passages. This immune-mediated inflammation is a protective response to perceived harmful stimuli.

Foreign bodies such as splinters activate a local immune response as the body attempts to remove or isolate them. This triggers swelling and tenderness at the site as inflammatory cells work to eliminate the foreign material and prevent infection, demonstrating inflammation's protective function.

Thermal injury from sunburn, burns, or frostbite damages skin cells and triggers inflammation. The damaged cells release inflammatory mediators, causing redness, warmth, and pain. This inflammatory response protects tissue by clearing damaged cells and initiating repair processes necessary for healing.

Chemical exposure to caustic agents like drain cleaner damages cell membranes and induces necrosis, triggering localized inflammation. Chemical burns result from this cellular injury, causing redness, swelling, and pain as the inflammatory response works to eliminate damaged tissue and prevent further injury.