Problem description:
What is granulation tissue and what are its characteristics?
Analysis:
Granulation tissue is composed of exuberant capillaries, fibrous connective tissue and various inflammatory cells. It is bright red, granular, soft and moist, and looks like fresh granulation, hence the name.
Microscopically, a large number of dilated capillaries formed by the proliferation of solid cell cords and endothelial cells grow perpendicular to the wound surface, forming a circular curved capillary network with arterioles as the axis. There are many new fibroblasts around the capillaries, and there are often a lot of exudates and inflammatory cells. Macrophages are often the main inflammatory cells, and there are also many neutrophils and lymphocytes, so granulation tissue has anti-infection function. Macrophages can secrete PDGF, FGF, TGF-β, IL- 1 and TNF, and PDGF released by platelets during wound coagulation can further proliferate into fibroblasts and capillaries. Macrophages and neutrophils can devour bacteria and tissue fragments. When these cells are destroyed, they release various proteolytic enzymes, which can decompose necrotic tissues and fibrin. Capillary endothelial cells in granulation tissue also have phagocytosis and strong fibrinolysis.
The cytoplasm of some fibroblasts in granulation tissue contains myofilaments, which have contractile function, so they should be called myofibroblasts. Fibroblasts produce matrix and collagen. There is more matrix in the early stage and more and more collagen in the later stage.