Tissue Injury: Inflammation and Repair

Wound repair occurs in four phases in animal tissue.

The first phase, hemostasis, starts immediately after an injury. Damaged blood vessels constrict, leading to reduced blood flow and hypoxia at the injury site. This attracts platelets and activates the clotting mechanism to help seal the wound. A blood clot further helps control bleeding and prevent infection.

The damaged cells at the wound site then signal immune cells to initiate the second phase, inflammation. Neutrophils and macrophages are recruited through the bloodstream to kill bacteria and remove debris. These cells release growth factors to begin the third phase, proliferation, and facilitate fibroblast migration from the surrounding tissue.

Fibroblasts divide, secrete collagen-rich extracellular matrix, and promote the reestablishment of the blood vessel network, leading to the formation of granulation tissue.

In the final phase of repair, remodeling, the wound contracts and most fibroblasts die. Then, the collagen fibers are rearranged into an organized and rigid structure, providing strength to the newly formed tissues.

The granulation tissue is gradually transformed into scar tissue that mimics normal tissue structure.