skin wound healing ( skin 10) Flashcards
what is wounds?
Physical break in the skin.
Tear, cut, erosion, puncture or ulcer
Break in the skin barrier function
- Loss of fluid, blood or heat (e.g. Large burns)
- Allows invasion of microorganisms (e.g. S. aureus, Cl. tetani)
- Toxin ingress
what are different trauma wound types?
Abrasion; graze. Superficial, epidermis scraped off
Laceration; irregular tear
Avulsion; removal of all skin layers by abrasion (bottom right)
Incision; regular slice with clean sharp object (e.g. knife, bottom left)
Puncture; e.g. Nail or needle
Amputation; cut off!
what are the 4 types of wound classifications
Necrotic: Dead (ischaemic) tissue, usually black and covered with dead epidermis
Sloughy: often yellow due to accumulation of cellular debris, fibrin, serum exudate, bacteria
Granulating: typically deep pink or red with a highly vascularised irregular granular appearance
Epithelialising: cells migrating from wound edges to start the process of re-epithelialisation, see a pink wound bed.
what are the different stages of wound healing?
- inflammation - characterised by redness, heat, pain and swelling
which lasts 4-5 days
initiates the healing process by stabilising the wound through platelet activity. - stops bleeding and triggers the immune response
Within 24 hours of the initial injury, neutrophils, monocytes and macrophages are on the scene to control bacterial growth and remove dead tissue
Characteristic red color and warmth is caused by the capillary blood system increasing circulation & laying foundation for epithelial growth
- proliferation - begins within 24 hours of the initial injury and continues for up 21 days.
Characterised by three events:
- Epithelialization
- Granulation
- Collagen synthesis - granulation
- Formation of new capillaries that generate and feed new tissue
angiogenesis
- Granulation tissue is “beefy” red tissue that bleeds easily
- Fibrous connective tissue that replaces the fibrin clot
- Grows from base of the wound - Epithelialisation
- Formation of an epithelial layer that seals and protects the wound from bacteria and fluid loss
- Essential to have a moist environment to foster growth of this layer
- Is initially a very fragile layer that can be easily destroyed with aggressive wound irrigation or cleansing of the involved area - collagen synthesis
-Creates a support matrix for the new tissue - provides new tissue its’ strength
- Oxygen, iron, vitamin C, zinc, magnesium & protein are vital for collagen synthesis
- This stage is the actual rebuilding of the skin barrier
influenced by the overall patient condition (age, nutrition etc)
And by condition of wound bed - wound contraction
Wounds contract ~ 1 week post injury
Fibroblasts differentiate into myofibroblasts
Cells mid-way between fibroblast and smooth muscle cell!
After healing, myofibroblasts are lost by apoptosis
If not, can give keloid scars
Contraction can last for weeks and continues even after the wound is completely re-epithelialised.
Large wounds can be 40 to 80% smaller after contraction.
Contraction usually does not occur symmetrically; most wounds have an ‘axis of contraction’ to align cells with collagen.
- maturation
- Final stage of wound healing
- Begins around day 21 and may continue for up to 2 years
- Maturation begins when collagen synthesis and degradation equalise.
- Type III collagen produced during proliferation, gradually degraded and replaced with stronger type I collagen
Originally disorganised collagen fibers are rearranged, cross-linked, and aligned along “tension lines”
Langer’s lines = direction in which the skin of a human cadaver will split when struck with a spike. Corresponds to the natural orientation of collagen fibres in the dermis.
Termed re-modelling
- During maturation, the tensile strength of the wound increases
-As activity at the wound site reduces, the scar loses its red appearance as blood vessels that are no longer needed are removed by apoptosis.
what are the types of wound healings?
Different categories of wound healing, but follow similar stages as described above.
Primary healing (also called healing by first intention, or primary wound closure)
Secondary healing (healing by secondary intention, or secondary wound closure)
Delayed primary healing (sometime called healing by third intent / tertiary intention)
what is primary wound closure?
When wound edges are brought together so that they are adjacent to each other (re-approximated)
Most surgical wounds heal by primary intention
Wound closure is performed with sutures (stitches), staples, or adhesive tape
Advantages:
Minimizes scarring
Lowers infection risk
what is secondary wound closure?
The wound is allowed to granulate
Surgeon may pack the wound with a gauze or use a drainage system
Granulation results in a broader scar than primary intent
Healing can be slowed due to drainage from infection
Wound care must be performed daily to encourage wound debris removal to allow for granulation tissue formation
Advantages:
Allows removal of foreign bodies
Prevents haematoma development (collection of blood outside of blood vessels that would be trapped when wound closed immediately by, for example, stitches)
what is delayed primary healing?
The wound is purposely left open
Wound is initially cleaned, debrided (remove dead, damaged or infected tissue) and observed.
By 4th day, phagocytosis of contaminated tissues is well underway, and epithelisation, collagen deposition, and maturation are occurring.
Usually the wound is closed surgically after 4-5 days,
But, if “cleansing” of the wound is incomplete, chronic inflammation can then occur
Results in significant scarring.
what is scars?
what is it made from?
Areas of fibrous tissue,
natural part of the healing process
All wounds result in some degree of scarring (often not obvious)
Scar tissue is from collagen, but is highly orientated rather than as a “basket weave”
So, weaker than random arrangement to future trauma, UV radiation etc
Sweat glands and hair follicles do not grow back within scar tissue.
If wound healing does not progress normally, e.g. myofibroblasts persist rather than cleared by apoptosis may get keloid or hypertrophic scars
what is hypertrophic scar?
Over-production of collagen during healing causing scar to be raised above skin surface.
Typically red raised lump on skin
Less common following surgery (“closure by intention”) and more common for wounds closed by “secondary intention”
May seek camouflage
what is keloids?
Overgrowth of collagen forming rubbery / shiny nodules that can be pink, red, brown. Often overgrow area of initial trauma
Can continue to grow indefinitely into large (benign) tumorous tissue
Keloid scars can be caused by surgery, an accident, by acne or, sometimes, from body piercings.
Are inert masses of collagen and therefore completely harmless and non-cancerous, but cosmetically unacceptable to some patients.
However, they can be itchy or painful in some individuals. They tend to be most common on the shoulders and chest.
what are atrophic scars?
causes
Atrophic scar: A sunken recess in the skin, which has a pitted appearance.
Caused when underlying structures supporting the skin (fat / muscle) are lost.
Often associated with acne, chickenpox but also found after some surgery
what are stretch marks
causes
Stretch marks (striae) are also a form of scarring.
Caused when the skin is stretched rapidly (e.g. during pregnancy, weight gain, adolescent growth spurts)
Also when skin is put under tension during the healing process, (usually near joints).
Appearance usually improves over time (years)
what is scar treatmemt?
Often for cosmetic reasons
Chemical peels: OK for superficial (e.g. acne) scars, but not for keloids or with infections in scars
Filler injections: can help appearance of atrophic scars (raise scar to skin level)
Dermabrasion: to remove top layer of scar tissue
Laser: non-ablative can heat and redistribute collagen in keloids. Ablative lasers remove outer skin layers, not recommended for keloids
Radiotherapy: low dose may help keloids but not recommended due to adverse effects
Ointments and pressure dressings: no strong evidence of benefits
Steroids: Topical steroids ineffective. Can inject steroid directly into scar. Some evidence that it thins and softens the scar
Surgery: Cut out scar, let new wound heal by intention (i.e. scar may have come from accident / trauma)
But, keloid scars often recur (45%)
