Грануляционная ткань как разновидность соединительных тканей (обзор)

Abstract

Currently, there is no consensus among scientists on the place of scar tissue and, in particular, granulation tissue in the classification of fibrous connective tissue. This paper aimed to generalize literature data on the structure and development of fibrous scar tissue. It is demonstrated that granulation tissue is mostly composed of myofibroblasts, along with fibroblasts, as well as old fibroblasts, endothelial cells, and immune cells. Myofibroblasts are characterized by a developed cytoskeleton represented by stress fibers, which ensures active migration of these cells and remodelling of the surrounding intercellular substance. The developed synthetic apparatus of the myofibroblast, in addition to synthesis of the intercellular substance, provides cell paracrine activity, which maintains the homeostasis of the cellular components of granulation tissue. The intercellular substance is represented by type III collagen fibers; elastic fibers are absent. The ground substance has a high degree of hydration and low stiffness and is rich in glycosaminoglycans, collagenases and fibronectin; this greatly facilitates the migration of myofibroblasts, endotheliocytes and fibrocytes. The ability of the intercellular substance to accumulate growth factors plays an important role in the transdifferentiation of fibrocytes into myofibroblasts. The blood vessels of the granulation tissue are the source of fibrocytes, which play a key role in the formation of granules of the newly formed tissue around the vessel. Myofibroblast apoptosis triggers the differentiation of granulation tissue into dense fibrous loose connective tissue. At the same time, type III collagen is replaced by type I collagen, elastin fibers appear, angiogenesis is inhibited, and mechanisms providing sympathetic innervation of connective tissue are triggered. Thus, granulation tissue can be considered as temporary connective tissue, which is one of the examples of dedifferentiation that occurs not only at the cellular, but also at the tissue level.