Inflammation: Introduction

Inflammation is a fundamental, protective biological response of vascularized tissues to cellular injury, infection, or harmful stimuli. Its primary function is to eliminate the initial cause of injury, clear necrotic cells and damaged tissue, and initiate the necessary repair processes.

Cardinal Signs

Acute inflammation presents with classic signs. Redness results from vasodilation and increased blood flow. Heat is due to increased metabolism and circulation. Swelling results from the accumulation of protein-rich fluid due to increased vascular permeability. Pain arises from mediators such as prostaglandins and bradykinin, which stimulate nerve endings. Loss of function reflects the combined effects of pain, swelling, and tissue damage.

Etiology of Inflammation

Inflammation is triggered by factors that cause cellular injury. Physical trauma (e.g., fractures, lacerations) leads to cell damage and release of intracellular contents. Chemical exposure to acids, alkalis, or toxins damages cell membranes and induces necrosis. Ischemia and infarction reduce oxygen supply, causing cell death and the release of danger signals that activate inflammation.

Microbial infections (bacteria, viruses, fungi, parasites) stimulate immune responses through pathogen-associated molecular patterns. Immune reactions, such as allergies or autoimmune diseases, also produce inflammation; for example, allergen binding to IgE on mast cells releases histamine. Thermal injury from burns or frostbite damages tissue, while foreign bodies (splinters, sutures, urate crystals) trigger inflammation as the body attempts to remove or isolate them.