Fig. 1

Phases of tissue regeneration. (A) Uninjured tissue. (B) Injury: injured area is shaded in gray, representing damaged and dead cells. The blood vessel in direct contact with the lesion is also damaged and is marked in a lighter red color than the healthy vessels. (C) Wound closure and immune response: the injured area is infiltrated by platelets to stop the bleeding resulting from injury to the blood vessels in the damaged area. At the same time, the lesion is also infiltrated by immune cells. (D) Clearing of debris and deposition of extracellular matrix (ECM): the immune cells start to clean the dead tissue and other debris resulting from the injury. Fibroblasts proliferate and produce ECM fibers that fill the cleared injury area to prevent the injury from collapsing. The formation of new blood vessels takes place (thinner red lines). (E) Resorption of ECM and cell proliferation: the ECM starts to be eliminated as the injury is repopulated by new cells through proliferation. (F) Regeneration: the injured area has been completely repopulated and the tissue reconstituted to its homeostatic condition. Cells undergo cell cycle arrest and very few proliferating cells can be seen.