Wound healing, or cicatrisation, is an intricate process in which the skin (or another organ-tissue) repairs itself after injury.In normal skin, theepidermis(outermost layer) anddermis(inner or deeper layer) exists in a steady-state equilibrium, forming a protective barrier against the external environment. Once the protective barrier is broken, the normal (physiologic) process of wound healing is immediately set in motion. The classic model of wound healing is divided into three or four sequential, yet overlapping,phases: (1)hemostasis(not considered a phase by some authors), (2) inflammatory, (3) proliferative and (4) remodeling.Upon injury to the skin, a set of complex biochemical events takes place in a closely orchestrated cascade to repair the damage.Within minutes post-injury, platelets (thrombocytes) aggregate at the injury site to form afibrinclot. This clot acts to control activebleeding(hemostasis). The speed of wound healing can be impacted by many factors, including the bloodstream levels of hormones such as oxytocin.
In the inflammatory phase, bacteria and debris arephagocytosedand removed, and factors are released that cause the migration and division of cells involved in the proliferative phase.
The proliferative phase is characterized byangiogenesis,collagendeposition,granulation tissueformation, epithelialization, and wound contraction.In angiogenesis, new blood vessels are formed by vascular endothelial cells.In fibroplasia and granulation tissue formation,fibroblastsgrow and form a new, provisionalextracellular matrix(ECM) by excreting collagen and fibronectin.Concurrently, re-epithelialization of the epidermis occurs, in which epithelial cellsproliferate and ‘crawl’ atop the wound bed, providing cover for the new tissue.
In contraction, the wound is made smaller by the action ofmyofibroblasts, which establish a grip on the wound edges and contract themselves using a mechanism similar to that in smooth muscle cells. When the cells’ roles are close to complete, unneeded cells undergo apoptosis.
In the maturation and remodeling phase, collagen is remodeled and realigned along tension lines and cells that are no longer needed are removed by apoptosis.
However, this process is not only complex but fragile, and susceptible to interruption or failure leading to the formation of non-healingchronic wounds. Factors which may contribute to this include diabetes, venous or arterial disease, old age, and infection.
Fascinating is a good word for healing — before you finished picking yourself up and brushing the gravel out of your knee, your body had already begun a complex process that will soon have you ready to blade again (perhaps with knee pads this time?).
The moment you cut or tear a blood vessel, the body’s Superheros of Healing spring into action. Here’s how healing works:
- First comesvasoconstriction— blood vessels leading to the wound tighten to reduce the flow of blood to the injured area.
- Platelets(triggered by enzymes leaked from the torn blood vessel) rush to the scene. These sticky blood cells clump to each other and then adhere to the sides of the torn blood vessel, making a plug.
- Clotting proteinsin the blood join forces to form afibrin netthat holds the platelet plug in place over the tear, and in just a few seconds or minutes (depending on how bad the scrape is),BLEEDING STOPS, thanks to coagulation! The fibrin plug becomes a scab that will eventually fall off or be reabsorbed into the body once healing is complete.
Once bleeding has been controlled, the next step is stopping infection:
- The blood vessels that were constricted now dilate to bringwhite blood cellsrushing to the scene. White blood cells engulf and destroy any germs that may have gotten into the body through the open wound.
When the enemies of blood loss and infection have been vanquished, the body turns its attention to healing and rebuilding:
- Fibroblasts(cells that are capable of forming skin and other tissue) gather at the site of injury and begin to producecollagen, which will eventually fill in the wound under the scab and create new capillaries to bring oxygen-rich blood to the recovering wound.
- Skinalong the edges of the wound becomes thicker and then gradually migrates (or stretches) under the scab to the center of the wound, where it meets skin from the other side and forms a scar (about three weeks after the initial injury).
- Scar tissuewill become stronger and fade gradually over the next several years as more collagen is added, but will only have about 80 percent of the strength of the original skin.
Not all wounds heal equally. Generally speaking, more serious wounds take longer to heal. Individual factors also influence how quickly your body is able to recover from a wound, including:
- Age— young’uns usually heal faster than older folks
- Nutrition— the body needs a good supply of vitamin C to make collagen
- Smoking— non-smokers, on average, heal more quickly than smokers
- Stress— large amounts of stress can delay the healing process
- Other infections or illnesses— diabetes, thyroid disease, high blood pressure, and poor circulation, for example, can decrease the body’s ability to heal
If you have wounds that are slow to heal, check with your health care provider. It could be a sign of an underlying illness.
via Ask Alice