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An inflammatory response is triggered by various damaging stimuli, including abrasions, chemical irritants, pathogens, and extreme temperatures. These injuries damage cells and connective tissue fibers, changing the chemical composition of interstitial fluid. Damaged tissues and resident immune cells then release inflammatory chemicals that initiate the response cascade.

Tissue mast cells release histamine and prostaglandins into the extracellular fluid following injury. Histamine increases vasodilation and permeability of nearby blood vessels, boosting blood flow and causing redness and heat. Increased vessel permeability allows plasma fluid to leak into surrounding tissues, creating swelling or edema.

Inflammatory chemicals act as chemotactic agents, attracting phagocytes like neutrophils and macrophages to the injury site. These cells migrate through permeable blood vessel walls via diapedesis and engulf pathogens, debris, and dead cells through phagocytosis. Macrophages also release cytokines that promote tissue repair and modulate the immune response.

Swelling from plasma fluid leakage creates pressure within the tissue. This pressure, combined with the action of prostaglandins, stimulates nerve endings and induces pain. The pain response is part of the inflammatory cascade that signals tissue damage and promotes protective behaviors.

Vasodilation increases blood flow to the affected area, enhancing enzymatic reactions and facilitating entry of clotting factors and complement proteins. This increased circulation boosts phagocyte activity and accelerates enzyme reactions that help damage foreign proteins and pathogens, supporting the body's defense mechanisms.

The inflammatory response must be tightly regulated to prevent chronic inflammation and excessive damage. Anti-inflammatory cytokines are released to counteract pro-inflammatory signals, while regulatory T cells modulate the immune response and prevent autoimmunity. The resolution phase involves clearance of apoptotic cells and debris, promoting tissue remodeling and restoration of function.

The cardinal signs and symptoms of inflammation are redness, swelling, heat, and pain. These occur due to vasodilation increasing blood flow, increased vessel permeability causing edema, and nerve stimulation from pressure and prostaglandins. Occasionally, loss of function may also accompany these signs.