Granulation tissue can begin to appear within 2 ~ 3 days after tissue injury, filling wound or organizing foreign body. With the passage of time, granulation tissue gradually matured according to its growth order. Its main morphological signs are: the water absorption is gradually decreasing; Inflammatory cells decreased and gradually disappeared; Capillary occlusion, the number decreased, and a few capillaries were reconstructed into arterioles and venules; Fibroblasts produce more collagen fibers and gradually become fibroblasts. With more and more collagen fibers, the scar formation process appears, and the scar is completely formed about one month after injury. Finally, granulation tissue matured into fibrous connective tissue and transformed into scar tissue.
Healthy granulation tissue is very important for epidermal regeneration, because it can provide nutrients and growth factors needed for epithelial regeneration. If granulation tissue can not fill the wound for a long time to form a scar, epithelial regeneration will be delayed; In another case, granulation tissue is overgrown due to foreign bodies and infection, which is higher than the skin surface and will also prevent epidermis from regenerating, so it is often necessary to remove it in clinic. If the wound is too large (generally considered to be larger than 20cm in diameter), it is difficult for the regenerated epidermis to completely cover the wound, and skin grafting is often needed.