Granulation tissue
From Freepedia
Granulation tissue is the tissue that replaces a fibrin clot in healing tissue. It is supported by a network of type III collagen, a weaker form of collagen, which is later replaced by the stronger long-stranded type I collagen. Granulation tissue also contains a number of cell types. Chief among these are fibroblasts, cells involved in immunity, and cells involved in vascularisation.
Immunity
Macrophages and neutrophils are the main immune cells present, although other leukocytes are also present. These work to phagocytize old or damaged tissue, and protect the healing tissue from pathogenic insult. This is necessary because not only is this tissue vulnerable due to the healing process, but also because (not being fully repaired) it often does not have an effective, intact barrier of skin to provide a first line of defence from invading pathogens.
Vascularisation
It is necessary for a network of blood vessels to be established as soon as possible to provide the growing tissue with nutrients, to take away cellular wastes, and transport new leukocytes to the area. Fibroblasts, the main cells that deposit granulation tissue, depend on oxygen to proliferate and lay down the new extracellular matrix. In vascularization, also called angiogenesis, endothelial cells quickly grow into the tissue from older, intact blood vessels. These branch out in a systematic way, forming anastomoses with other vessels.
