Wound healing refers to the healing process after the body is subjected to external force, and the skin and other tissues are broken or damaged, including the regeneration of various tissues and the complex combination of granulation tissue hyperplasia and scar tissue formation, showing the synergy of various processes.The basic process of wound healing: acute inflammation → cell proliferation → scar formation → epidermal and other tissue regeneration.According to the degree of injury and infection, wound healing can be divided into three types: primary healing, secondary healing, and tertiary healing.
According to the nature and treatment of the damaged tissue, wound healing can be divided into three types.Primary healing: it can be seen in the wounds with few tissue defects, neat wound margins, no infection, and tight wound alignment after bonding or suture, such as surgical incision.There is only a small amount of blood clots in this kind of wound, and the inflammatory reaction is slight. The epidermal regeneration can cover the wound within 24-48 hours.The granulation tissue can grow from the edge of the wound on the third day and fill the wound quickly. The collagen fiber is formed on the fifth to sixth day (the suture can be removed at this time), and it will heal completely in about two to three weeks, leaving a linear scar.The time of primary healing is short and scarring is less.
Secondary healing: it can be seen in the wound with large tissue defect, irregular wound margin, split, irregular union, or infection.The healing of this kind of wound is different from the primary healing as follows: ① There are many necrotic tissues or infection, which continue to cause local tissue degeneration, necrosis and obvious inflammatory reaction.Regeneration can start only after the infection is controlled and the necrotic tissue is cleared; ②The wound is large, with obvious contraction, and a large amount of granulation tissue grows from the bottom and edge of the wound to fill the wound; ③The healing time is longer and the scar is larger.
Under scab healing: the blood, exudate and necrotic substances on the wound surface dry to form a dark brown hard scab, and the above healing process is carried out under the scab.After the epithelial regeneration is completed, the scab will fall off.The healing time under the scab is usually longer than that without scab, because the epidermal regeneration at this time must first dissolve the scab skin, and then grow forward.The dried crust is not conducive to the growth of bacteria, so it has a certain protective effect on the wound.However, if there are many exudates under the scab, especially when there is bacterial infection, the scab skin will become an obstacle to the drainage of exudates, aggravating the infection and not conducive to healing.
Healing process
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The minimal trauma is limited to the epidermal layer of the skin, and in the slightly severe cases, the skin and subcutaneous tissue are broken, with wounds;Severe trauma may include muscle, tendon, nerve rupture and fracture.The following is the basic process of wound healing.
1. Acute inflammation stage: the early changes of the wound. The local wound has varying degrees of tissue necrosis and blood vessel rupture and bleeding. Within a few hours, there will be inflammatory reactions, which are manifested as congestion, serous exudation and white blood cell migration, so the local area is red and swollen.The white blood cells were mainly neutrophils, and then turned to macrophages after 3 days.The fibrinogen in the blood and exudate in the wound quickly coagulates to form clots. Some clots dry to form scabs. The clots and scabs play a role in protecting the wound.
2. Cell proliferation stage: after 2-3 days of wound contraction, the whole layer of skin and subcutaneous tissue at the edge of the wound moved to the center, so the wound shrank rapidly until it stopped about 14 days later.The purpose of wound contraction is to shrink the wound, even 80%. However, the degree of wound reduction varies with the animal type, wound site, wound size and shape under various specific circumstances.Wound contraction is caused by the traction of the newly born myofibroblasts at the edge of the wound, and has nothing to do with collagen.Because the time of wound contraction is just the time of myofibroblast proliferation.5-hydroxytryptamine (5-HT), angiotensin and norepinephrine can promote wound contraction, while glucocorticoid and smooth muscle antagonists can inhibit wound contraction.Inhibition of collagen formation has no effect on wound contraction. Skin grafting can stop wound contraction.
3. Scar formation stage: granulation tissue hyperplasia and scar formation begin from about the third day, granulation tissue grows from the bottom and edge of the wound to fill the wound.Capillaries grow at a rate of 0.1-0.6 mm per day, and their directions are mostly perpendicular to the wound surface, and they are looped.There are no nerves in the granulation tissue, so there is no sensation.From the 5th to the 6th day, fibroblasts produce collagen fibers, and the collagen fiber formation is very active in the following week, and then gradually slows down.With more and more collagen fibers, the scar formation process occurs, and the scar is completely formed about one month after the injury.The collagen fibers in the scar are finally parallel to the skin surface, possibly due to the effect of local tension.
Scar can make the wound edge combine firmly.The local tensile strength of the wound began to increase shortly after the injury. The tensile strength increased rapidly in the 3rd to 5th week and then slowed down. The tensile strength reached the peak around 3 months and did not increase any more.However, it still only reaches 70%~80% of the normal skin strength.The tensile strength of wound may be mainly determined by the amount and arrangement of collagen fibers, and also related to some other tissue components.After the abdominal wall incision is healed, if the scar formation is weak, the tensile strength is low, and the scar tissue itself lacks elasticity, the effect of intraperitoneal pressure can sometimes make the healing mouth gradually bulge out, forming abdominal wall hernia.Similar conditions can also be seen in the larger scars of the myocardial and arterial walls, which can form ventricular aneurysm and aneurysm.
4. Regeneration of epidermis and other tissues: within 24 hours after the trauma, the epidermal base at the edge of the wound proliferates, and moves toward the center of the wound under the clot to form a single layer of epithelium, covering the surface of granulation tissue. When these cells meet each other, they stop advancing, and proliferate and differentiate into squamous epithelium.Healthy granulation tissue is very important for epidermal regeneration, because it can provide nutrition and growth factors needed for epithelial regeneration. If granulation tissue cannot fill the wound and form scar for a long time, epithelial regeneration will be delayed;In another case, the excessive granulation tissue caused by foreign body and infection is higher than the skin surface, which will also prevent epidermal regeneration. Therefore, it is often necessary to remove it in clinical practice.If the wound is too large (diameter>20cm), it is difficult for the regenerated epidermis to completely cover the wound, and skin grafting is often required.
If the skin appendages (hair follicles, sweat glands and sebaceous glands) are completely damaged, they cannot be completely regenerated and scar repair occurs.After the tendon breaks, it is also a scar repair at the initial stage, but with the continuous reconstruction of functional exercise, the collagen fibers can be arranged in the direction of the original tendon fibers to achieve complete regeneration.
Factors affecting regeneration and repair
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It can be seen from the above that the degree of injury and tissue regeneration ability determine the repair mode, healing time and scar size.The treatment principle should be to shrink the wound surface (such as the suture wound) as soon as possible, prevent re injury and promote tissue regeneration.Although the regeneration ability of tissue is acquired in the process of evolution, it is still affected by systemic and local conditions.Some unfavorable factors should be avoided and favorable conditions should be created to promote tissue regeneration and repair.Scar tissue can cause harm under certain conditions, so it is sometimes necessary to inhibit the formation of scars or promote the absorption of scars.
The factors affecting regeneration and repair include systemic factors and local factors.
1. Systemic factors
(1) Age: Teenagers have strong tissue regeneration ability and fast healing.The elderly, on the contrary, have poor tissue regeneration ability and slow healing, which is closely related to the elderly's angiosclerosis and blood supply reduction.
(2) Nutrition: severe protein deficiency, especially the deficiency of sulfur-containing amino acids (such as methionine and cystine), results in poor formation of granulation tissue and collagen and delayed wound healing.Among vitamins, vitamin C is the most important for healing.This is because proline and lysine, the two main amino acids in the α - polypeptide chain, must be hydroxylated by hydroxylase to form procollagen molecules, while vitamin C has the role of catalyzing hydroxylase, so it is difficult to form procollagen molecules when vitamin C is lacking, thus affecting the formation of collagen fibers.Zinc in trace elements plays an important role in wound healing. The content of zinc in skin of patients with delayed wound healing after surgery is mostly lower than that of patients with good wound healing.In addition, it has been proved that the excretion of zinc in the urine of patients with surgical stimulation, trauma and burn increases, and zinc supplementation can promote healing.The mechanism of zinc action is not very clear, which may be related to the fact that zinc is a component of some intracellular oxidase.
2. Local factors
(1) Infection and foreign bodies: infection greatly hinders regeneration and repair: many pyogenic bacteria produce some toxins and enzymes, which can cause tissue necrosis and matrix or collagen fiber dissolution.This not only aggravates local tissue damage, but also hinders healing.When the wound is infected, there are many exudates, which can increase the tension of the local wound, often make the wound being healed or the wound that has been stitched open, or cause the infection to spread and aggravate the damage.The infected wound cannot be sutured and should be drained as soon as possible. Only when the infection is controlled can the repair be carried out.Necrotic tissue and other foreign bodies also hinder the healing and are conducive to infection.If the wound is infected, or there are many necrotic tissues and foreign bodies, it must be secondary healing.In clinical practice, debridement is performed to remove necrotic tissue from large wounds that have been contaminated by bacteria but have not yet been significantly infected, so as to narrow the wound and shorten the healing time of wounds that should have been healed in the second phase, or even reach the first phase.
(2) Local blood circulation: on the one hand, it ensures the oxygen and nutrition required for tissue regeneration, on the other hand, it also plays an important role in absorption of necrotic substances and control of local infection.When the local blood flow supply is good, the regeneration and repair are good. On the contrary, if there is atherosclerosis or varicose veins in the lower limbs and other diseases that make the local blood circulation poor, the wound healing is slow.The clinical application of some drugs, such as wet compress, hot compress, sticking Chinese medicine and taking Chinese medicine for promoting blood circulation and removing stasis, can improve local blood circulation.
(3) Nerve innervation: complete nerve innervation has certain effect on tissue regeneration.For example, ulcers caused by leprosy are not easy to heal because of nerve involvement.Autonomic nerve injury changes the local blood supply and has a more obvious impact on regeneration.
(4) Ionizing radiation: can destroy cells, damage small blood vessels, inhibit tissue regeneration, and prevent scar formation.
