Chapter 7 Organization, granulation tissue and fibrosis
Organization is the process by which granulation tissue replaces damaged tissue or inanimate material such as blood clot. The granulation tissue then matures into a scar. The term fibrosis is used for healing by scar formation via this mechanism. Organization occurs when:
Components of granulation tissue
The three principal constituents of granulation tissue are endothelial cells, fibroblasts and myofibroblasts, and macrophages (Fig. 3.7.1). Other cells are also present in most cases, the type depending on the aetiology of the granulation tissue formation. For example, abundant inflammatory cells will be found in the granulation tissue at the base of a chronic peptic ulcer.
Fig. 3.7.1 Granulation tissue. (A) Components in granulation. (B) Oedematous connective tissue containing fibroblasts and inflammatory cells.
Endothelial cells grow into the exudate or dead tissue to vascularize it. This process of blood vessel formation is known as angiogenesis or neovascularization. The endothelial cells initially form solid cords, but they soon develop lumina and become capillaries. Indeed, the term granulation tissue comes from the granular appearance imparted by loops and coils of newly formed capillaries. The new endothelial cells are derived from two sources: