Chapter 9: Inflammation, Tissue Repair & Wound Healing

Inflammation serves as the body’s essential, dynamic defense mechanism, involving vascularized tissues reacting to injury by eliminating the harmful agent and initiating subsequent tissue repair. The local signs of acute inflammation—redness, heat, swelling, pain, and loss of function—arise from two interwoven stages: the rapid vascular phase involving temporary vasoconstriction followed by vasodilation and increased capillary permeability, leading to fluid exudation; and the cellular phase, where leukocytes, primarily neutrophils, are recruited through adhesion and transmigration to perform host defense via chemotaxis and phagocytosis. This complex process is regulated by numerous chemical mediators, including preformed agents like histamine, newly synthesized lipid mediators such as prostaglandins and leukotrienes, and powerful cytokines like TNF-α and IL-1, which also drive systemic manifestations like the acute-phase response and fever. In contrast, chronic inflammation is prolonged, characterized by the dominance of mononuclear cells, including macrophages and lymphocytes, and often leads to the proliferation of fibroblasts, fibrosis, and tissue necrosis, sometimes forming specialized granulomas to isolate indigestible foreign material. Following the inflammatory process, tissue repair occurs either through regeneration, where injured cells are replaced by the same cell type (possible only for labile and stable cells), or by fibrous tissue replacement for fixed/permanent cells, resulting in a scar. Wound healing proceeds through three major phases—inflammatory, proliferative (marked by fibroblast activity, collagen deposition, and new capillary growth forming granulation tissue), and remodeling (where scar tissue tensile strength increases)—which differ based on the extent of tissue loss (primary vs. secondary intention healing). Optimal wound repair is highly susceptible to various inhibiting factors, including inadequate nutrition (especially protein and Vitamin C deficiency), impaired blood flow and oxygen delivery (ischemia), infection, foreign bodies, and the physiological changes associated with advanced age.