Granulation tissue is rich in collagen, and forms at an injury site. As the body tries to heal, this tissue eventually fills up the injury site, and also may lead to the formation of a scar. This scar may fade over time, as is often seen in cases where the wound is small. This is one of the most important wound healing stages.
After any kind of injury, the body tries to heal, and hence, tries to repair the damage that has been done. At first, new endothelial cells begin to proliferate, and this initiates the formation of the granulation tissue. This is seen within three to five days of injury. This tissue appears pink in color due to presence of angiogenesis (proliferation of new blood vessels), production of extra cellular matrix, and fibrosis. Basically, the laying down of a foundation of this tissue, which will eventually cover up the entire wound, is mostly in the form of a scar.
This tissue basically consists of fibroblasts and new blood vessels. It is composed of tissue matrix, which supports a variety of cells, and is created and modified by the fibroblasts. It initially consists of a weak network of type III collagen, and is later replaced by the stronger and longer stranded type I collagen. The latter one is generally seen in scar tissue. The immune cells present in this tissue are active cells, and are a part of the first line of defense for our body. These are neutrophil granulocytes, macrophages, lymphocytes, and some plasma cells. All these units vary depending on the stage of tissue formation, and on the presence or absence of an infection. These cells are chiefly seen in inflammatory reactions, and are also present as the wound is open, and hence, is susceptible to infections. These cells phagocytize old and damaged tissue, and thus, protect the newly forming body cells, minimizing the chances of an infection. This aids in the healing process, and speeds it up.
The reason why there is an increase in blood vessel formation, is because the growing cells and tissues need more amount of oxygen and nutrients. This blood also helps to drain away the waste products, like phagocytosed cells and other foreign materials. The fibroblasts need a lot of oxygen to lay down the new extracellular matrix. As the tissue matures, the fibroblasts become more and more inactive, and eventually become the chief cells present in the final scar tissue.
Excess of Granulation Tissue
Ideally, when wound care is undertaken properly, healing takes place gradually, and eventually, after scar formation, there is complete closure of the wound. However, sometimes there may be excess of granulation tissue formed, a condition which is known as caro luxurians, or proud flesh. This condition is usually treated with the help of topical applications, which help to cauterize off the excess tissue, so as to prevent any further proliferation and growth. Thus, it helps to make the body move into the next stage, i.e., from the formation of tissue to wound healing.
Sometimes, people who have permanent catheters may develop granulation tissue around the site of implant, because the body may wrongly identify it as a wound, which is not healing. This is especially seen if an implant is not fitted properly. In some cases, granulation tissue forms inside the body, and may even lead to stenosis or narrowing. However, on most occasions, the appearance of this tissue is a good sign, as it indicates that the body is trying to overcome the injury, and is healing.