What is Tissue repair? Steps involved in tissue repair.

 Tissue Repair:

Critical to the survival of an organism is the ability to repair the damage caused by toxic insults and inflammation. In fact, the inflammatory response to microbes and injured tissues not only serves to eliminate these dangers but also sets into motion the process of repair.

Repair of damaged tissues occurs by two types of reactions: regeneration by proliferation of residual (uninjured) cells and maturation of tissue stem cells, and the deposition of connective tissue to form a scar.

 1. Regeneration:  Some tissues are able to replace the damaged components and essentially return to a normal state; this process is called regeneration. Regeneration occurs by proliferation of cells that survive the injury and retain the capacity to proliferate, for example, in the rapidly dividing epithelia of the skin and intestines, and in some parenchymal organs, notably the liver.

2. Connective tissue deposition (scar formation):  If the injured tissues are incapable of complete restitution, or if the supporting structures of the tissue are severely damaged, repair occurs by the laying down of connective (fibrous) tissue, a process that may result in formation of a scar.

What are the systemic effects of inflammation?

Inflammation, even if it is localized, is associated with cytokine-induced systemic reactions that are collectively called the acute-phase response.

1. Fever: Cytokines (TNF, IL-1) stimulate production of PGs in hypothalamus.

2. Production of acute-phase proteins: C-reactive protein & others; synthesis stimulated by cytokines (IL-6 & others) acting on liver cells.

3. Leukocytosis: Cytokines (CSFs) stimulate production of leukocytes from precursors in the bone marrow.

4. In some severe infections, septic shock: Fall in blood pressure, disseminated intravascular coagulation, metabolic abnormalities; induced by high levels of TNF and other cytokines.