93. Granulation tissue: causes, macro- and microscopic features, biological properties.

Granulation tissue is the initial stage of connective tissue regeneration, being essentially a young connective tissue rich in cells and blood vessels, and poor in collagen fibers.

Normally, without damage, there is no granulation tissue in the body.

The formation of granulation tissue begins with the proliferation (division) of mesenchymal cells and neoplasms of blood microvessels. Macroscopically, it has the appearance of a delicate, juicy tissue of a reddish color, with a granular surface (hence the name), these grains represent newly formed vessels. It bleeds easily due to the large number of capillaries. In dynamics, the number of cells and blood vessels gradually decreases, mesenchymal cells turn into epithelioid cells, and the latter into fibroblasts. Fibroblasts predominate in the granulation tissue at the maturation stage, and the number of vessels is gradually decreasing. In parallel, fibroblasts are activated and collagen fibers are intensively formed, vessels turn into arteries and veins. The process of maturation of granulation tissue ends with the formation of mature fibrous connective tissue (scar tissue), which contains a small number of fibrocytes and blood vessels. Neoplasm of granulation tissue occurs not only during regeneration of the connective tissue itself, but also during incomplete regeneration of other organs, when the defect is replaced by connective tissue, as well as during organization, encapsulation, wound healing and productive inflammation.

There are 6 layers in the structure of granulation tissue:

• The surface leukocyte-necrotic layer. It consists of leukocytes, detritus and exfoliating cells. It exists throughout the entire healing period of the wound.

• A layer of vascular loops. It contains polyblasts in addition to blood vessels. With a prolonged course of the wound process, collagen fibers can form in this layer, located parallel to the surface of the wound.

• A layer of vertical vessels. It is built of perivascular elements and amorphous intertidal matter. Fibroblasts are formed from the cells of this layer. This layer is most pronounced in the early period of wound healing.

• The maturing layer is essentially a deeper part of the previous layer. Here, the periovascular fibroblasts take a horizontal position and move away from the vessels, collagen and argyrophilic fibers develop between them. This layer, characterized by polymorphism of cellular formations, remains the same thickness throughout the entire wound healing process.

• A layer of horizontal fibroblasts. A direct continuation of the previous layer. It consists of more monomorphic cellular elements, is rich in collagen fibers and gradually thickens.

• The fibrous layer. Reflects the process of maturation of granulations.

The inflammatory process ends with the maturation of granulations and the formation of mature tissue.

Meaning:

- wound defect replacement: it is the main plastic material that quickly fills the wound defect;

- protection of the wound from the penetration of microorganisms and foreign bodies: achieved by the content of a large number of leukocytes and macrophages in it and the dense structure of the outer layer;

- sequestration and rejection of necrotic tissues, which is facilitated by the activity of leukocytes, macrophages and the release of proteolytic enzymes by cellular elements.

The granulation tissue that filled the wound cavity is gradually transformed into mature coarse—fibrous connective tissue - a scar is formed.

When exposed to any adverse factors affecting the healing process (deterioration of blood supply, oxygenation, decompensation of the function of various organs and systems, repeated development of the purulent process, etc.), the growth and development of granulations, and epithelialization fade away. Granulations become pathological. Clinically, this is represented by the absence of wound contraction and a change in the appearance of granulation tissue. The wound becomes dull, pale, sometimes cyanotic, loses turgor, and is covered with a coating of fibrin and pus.