Edited by Dr. Lorenzo Boscariol
Wound healing represents our body's ability to repair damaged tissue. It can take place by regeneration (damaged cells are replaced with cells of the same type), or by replacement with connective tissue (fibrosis). In the first case, generally the repair does not give rise to significant scarring, while in the second case there is the formation of a permanent scar. Apart from a very few tissues almost exclusively made up of non-proliferating cells, the great majority of other tissues are made up of different cell populations, some of which actively proliferating, others quiescent but which can proliferate, and still others absolutely unable to proliferate.
The cells, based on their replicative capacity, can be classified into labile cells (in active proliferation), stable (normally quiescent but able to resume proliferation), and perennial (definitively exited from the cell cycle and therefore unable to proliferate). This subdivision also allows us to classify the tissues of our organism, on the basis of their histological origin, into labile, stable or perennial tissues. The lining epithelia, the mucosecerning epithelia, and the hematopoietic cells are typically labile. it resides in a rich set of stem cells that maintain intact the ability to undertake different differentiation paths. The parenchymal cells of the glandular organs (liver, kidneys, pancreas), the mesenchymal cells (fibroblasts and smooth muscle cells), the vascular endotheles are typically stable Neurons and muscle, skeletal and cardiac cells are perennial cells.
The ability of labile and stable cells to proliferate does not in itself imply the reconstitution of the normal tissue architecture during the repair process. with the connective structures, and in particular with the basement membrane, for example in the case of the epithelial tissues. The destruction of the basement membrane profoundly alters the polarity of growth and the reciprocal relationships of the epithelial cells, and this makes it very difficult to restore the original architecture tissue. In the case of perennial cells (and tissues), a modest proliferative activity is present in the skeletal striated muscle, by the peripheral satellite cells, but there is rarely an efficient regeneration. Often there is repair of the damage with the formation of a fibrous scar. Finally, in the central nervous system the damaged neurons are replaced by the proliferation of glial cells.
In wound healing there is always the more or less extensive formation of a fibrous scar, due precisely to the pivotal role of the connective tissue in re-establishing the interrupted tissue continuity. The wound healing modality will determine whether the scar will be more or less wide, more or less visible on external inspection, or more or less damaging to the mechanical properties of the tissue. As we will see later, wound repair is a highly similar process. to the inflammatory response (indeed some consider it a sort of "physiological inflammation"), whose resolution (including scarring) is inevitably influenced by the "intensity, duration and dominant cellular elements. The biochemical and molecular mechanisms are qualitatively always the same, and the biological meaning is the same: to restore, first temporarily and then permanently, the tissue integrity.
In the overall repair process, three components that are partially functionally and temporally separated can be recognized: the hemostasis phase, the inflammation phase and the regeneration phase. However, it is important to underline that these components can only be separated very schematically, and that in most cases they are, on the contrary, intimately interconnected. for wound healing: by first intention or by second intention (where the "intention is that ideally" manifested "by the wound to follow" one or "other path). It is important to underline that these two modalities differ essentially in the" extent of the reparative phenomena, but not for the mechanisms involved, which are basically the same.
Healing by primary intention is by far the most favorable: the wound is clean (not infected), with sharp edges, close together, juxtaposed, with little loss of substance. In the case of surgical wounds or sutured accidental ones, the margins are carefully matched with the use of sutures, a procedure that further facilitates the repair.
Healing by secondary intention is typical of those wounds characterized by extensive loss of substance or bacterial infections. In this case an intense inflammatory response is evoked, and there is a massive production of granulation tissue to repair the extensive loss of substance. Both of these phenomena profoundly alter the normal repair process and cause important scarring.
Other articles on "Healing of Wounds"
- Wound Healing - Primary Intention Repair
- Wound healing - Evolution of the reparative process
- Wound healing - scar phase