Healing

==Wound healing==
{{main|Wound healing}}
{{see also|Scar free healing}}
[[File:Haavoittuneita Punaisen ristin sairaalassa Tampereella (26901645371).jpg|thumb|Wounded patients at the [[Red Cross]] Hospital in [[Tampere]], [[Finland]] during the 1918 [[Finnish Civil War]]]]
In response to an incision or wound, a [[Wound healing|wound healing cascade]] is unleashed.  This cascade takes place in four phases: clot formation, inflammation, proliferation, and maturation.

===Clotting phase===
Healing of a wound begins with [[clot]] formation to stop bleeding and to reduce infection by bacteria, [[virus]]es and [[fungi]]. Clotting is followed by [[neutrophil]] invasion three to 24 hours after the wound has been incurred, with [[mitosis|mitoses]] beginning in [[epithelium|epithelial]] cells after 24 to 48 hours.{{citation needed|date=July 2011}}

===Inflammation phase===
In the inflammatory phase, [[macrophage]]s and other [[phagocytosis|phagocytic]] cells kill bacteria, debride damaged tissue and release chemical factors such as [[growth hormone]]s that encourage fibroblasts, [[epithelial cell]]s and endothelial cells which make new [[capillary|capillaries]] to migrate to the area and divide.{{Citation needed|date=May 2022}}

===Proliferative phase===
In the proliferative phase, immature [[granulation tissue]] containing plump, active fibroblasts forms. Fibroblasts quickly produce abundant type III [[collagen]], which fills the defect left by an open wound. Granulation tissue moves, as a wave, from the border of the injury towards the center.{{Citation needed|date=May 2022}}

As granulation tissue matures, the fibroblasts produce less collagen and become more spindly in appearance. They begin to produce the much stronger type I collagen. Some of the fibroblasts mature into myofibroblasts which contain the same type of [[actin]] found in [[smooth muscle]], which enables them to contract and reduce the size of the wound.{{Citation needed|date=May 2022}}

===Maturation phase===
During the maturation phase of wound healing, unnecessary vessels formed in granulation tissue are removed by [[apoptosis]], and type III collagen is largely replaced by type I. Collagen which was originally disorganized is cross-linked and aligned along tension lines. This phase can last a year or longer. Ultimately a scar made of collagen, containing a small number of fibroblasts is left.{{Citation needed|date=May 2022}}