Chapter 4: Tissue Repair & Wound Healing

Tissue Repair & Wound Healing educational overview of tissue repair delves into the biological processes governing how the body restores architecture and function following injury, a critical concept in general pathology. The discussion begins by outlining the five overlapping phases of repair: hemostasis, inflammation, regeneration, fibrosis, and remodeling. A key focus is placed on the role of the extracellular matrix (ECM) as a biological scaffold, composed of collagens, elastins, and glycoproteins. The lecture categorizes tissue regenerative capacity into three distinct cell types: labile cells (such as hematopoietic and surface epithelial cells) which replicate continuously; stable cells (like hepatocytes and endothelial cells) which are quiescent but can proliferate upon stimulation; and permanent cells (including neurons and cardiac muscle) which lack replicative potential, necessitating repair via fibrosis rather than regeneration. The biochemical pathways of scar formation are analyzed, highlighting the influence of growth factors such as VEGF and FGF in angiogenesis, and TGF-beta and PDGF in fibroblast activation and ECM deposition. Furthermore, the summary differentiates between healing by primary union, used for surgically closed wounds, and secondary union, which relies on wound contraction mediated by myofibroblasts. Organ-specific repair mechanisms are also detailed, contrasting hepatic regeneration and cirrhosis with cardiac fibrosis, pulmonary type II pneumocyte proliferation, and neural gliosis mediated by astrocytes. Finally, the text addresses clinical aberrations in wound healing, distinguishing between hypertrophic scars and keloids—noting the latter's genetic predisposition, frequent location on earlobes, and excess production of type III collagen—as well as factors leading to delayed healing like diabetes and infection.