Wound healing
In the human body sequence of events takes place to ensure that when an injury occurs, the wound will heal.
Within the endogenous fluids of the body, every cell and chemical mediator is a program and ready to act when needed when the conditions are normal the body is equipped to heal itself.
Phases of Healing
The phases are not entirely distinct.
The number of days to complete each phase will vary based on various factors such as age, size of the wound, co-morbidities, continued trauma, nutrition, blood flow, medications, stress, and infection.
The process of repair is the same for all wounds but the sequence will be much quicker in more shallow wounds with less tissue loss.
In all stages of healing, wounded tissues are striving to achieve homeostasis.
Inflammation (Phase I)
The normal immune system reaction towards injury.
Temporary repair initiated by coagulation (clotting factors, platelets) and short-term decreased blood flow.
Necrosis occurs after cells have been injured or destroyed.
If the wound is acute, some peri-wound edema, erythema, and drainage can be expected. If fluid accumulates at the injury site it is pus.
Oxygen is delivered via increased blood flow to keep the phagocytic cells alive and functioning.
Permanent repair is facilitated by creating a clean wound, setting the stage for the next phase of healing; re-epithelialization can begin.
Time frame: day of injury to approximately 10 days.
The rate of the inflammatory process is affected by the size of the wound, blood supply, available nutrients, and the extrinsic environment.
If this phase is interrupted or delayed, chronic inflammation can result.
Proliferation (Phase II)
New tissue fills in the wound as fibroblasts secrete collagen.
Skin integrity is restored by re-epithelialization and/or contraction.
Angiogenesis occurs: new blood vessel growth from endothelial cells, fragile capillary buds grow into the wound bed; new reddish, slightly bumpy tissue is called granulation tissue.
Epithelial cells differentiate into type I collagen.
Collagen synthesis occurs but the resulting new scar tissue is fragile and must be protected from trauma during this phase.
Time frame: 3 days of injury to approximately 20 days.
The rate of proliferation is affected by the size of the wound, blood supply, nutrients, and the extrinsic environment.
If this phase is interrupted or delayed, the result may be a chronic wound.
Maturation/remodeling (Phase III)
Maturation or remodeling of new tissue begins while granulation tissue is forming during the proliferative phase.
Epithelial cells continue to differentiate into Type-I collagen.
The new skin has tensile strength that is 15% of normal. Scar tissue is rebuilding but it reaches 80% of original tensile strength.
Underlying granulation tissue is replaced by less vascular tissue.
In deep wounds, dermal appendages are rarely repaired (hair follicles, sebaceous and sweat glands, nerves) but instead they are replaced by fibrous tissue.
Over time the scar tissue matures, changing from red to pink to white and from raised and rigid to flat and flexible.
Time frame: approximately 9 days of injury for up to 2 years.
The rate of maturation/remodeling is affected by the size of the wound, blood supply, available nutrients, and the extrinsic environment.
Factors affecting Healing
Two types of factor influence wound healing:
A. Local factors:
Infection effect locally which delays the process of healing
Poor blood supply to wound slow healing
Foreign bodies including sutures interfere with healing and cause intense inflammatory reaction infections
Moisture softens wound scab and eschar For more
Movement delays wound healing e
Exposure to ionizing radiations delay granulation tissue formation
Exposure to ultraviolet ray facilitates healing
Type, size, and location of injury determine the rate of healing.
B. Systemic factors:
Age. wound healing is rapid in a young age than old age due to poor blood supply to the injured area in the later nutrition
Nutrients must be present for the wound to heal include;
iron, vitamin B12, folic acid: essential for the delivery of oxygen to the tissue by red blood cells.
Vitamin C and zinc; essential for tissue repair
Vitamin A; essential to stimulate collagen cross-linking and
Arginine enhances healing and immune function.
High protein intake provides the amino acid required to build new tissue.
Systemic infection delays wound healing
Administration of glucocorticoid has an anti-inflammatory effect.
Uncontrolled diabetes are more prone to develop infections and delay in healing
Hematologic abnormality.
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