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Tissue Repair and Wound Healing Cheat Sheet by

Stages of wound healing

Three Phases of Wound Healing

1) Inflam­matory Phase
Immediate to 2-5 days; hemostasis and inflam­mation
 
Starts with clot formation and the migration of phagocytic wbc in the wound site. First cells to arrive are neutro­phils which ingest and remove bacteria and cellular debris. After 24 hours, macrop­hages come and ingest cellular debris and play a role in production of growth factors for prolif­erative phase
 
Granul­ation tissue fills any void. Collagen present but oriented vertic­ally. Prolif­eration of epithelial cells continue leading to thicker epithelial layer
2) Prolif­erative Phase
2 days to 3 weeks; granul­ation, contra­ction, epithe­lia­liz­ation
 
Focus is to build new tissue to fill the wound space.P­ro­lif­eration of fibrob­lasts and vascular endoth­elial cells to form granul­ation tissue which fills the wound space.
 
Fibrob­lasts synthe­sizes and secretes the collage, proteo­gly­cans, and glycop­roteins needed for wound healing. They also produce growth factors that induce angiog­enesis and endoth­elial cell prolif­eration and migration.
 
Epithe­lia­liz­ation is the final component where epithelial cells at the wound edges prolif­erate to form a new surface layer. Requires a moist vascular wound.
3) Remode­lling Phase
3 weeks to 1 year; collagen formation, increase in tensile strength
 
Develo­pment of the fibrous scar. There is a decrease in vascul­arity and continued remode­lling of scar tissue by simult­aneous synthesis of collagen by fibrob­lasts and lysis by collag­enase enzymes. These two processes lead to the scar becoming reoriented to increase its tensile strength.
*Granu­lation tissue is formed from the prolif­eration of fibrob­lasts and vascular endoth­elial cells. It contains capill­aries, fibrob­lasts and residual inflam­matory cells.
*At Day 4-5 of wound healing, the epidermis resumes normal thickness and begins kerati­niz­ation process.
*Excessive granul­ation tissue- when it continues to reproduce itself and forms and extends above the border and prevent proper epithe­lia­liz­ation. Therefore, the wound cannot heal.

Types of Wound Healing

Primary Intention Healing
Healing by a non-in­fected and uninte­rrupted surgical incision
 
Typically held by sutures or other physical support
 
Not as much cell death or tissue loss, very predic­table healing
Second Intention Healing
Requires removal of necrotic tissue due to increased cell death
 
Much slower healing process, leads to scar tissue

Wound Healing in short

Vascular Response
hemostasis - Goal is to control bleeding
Inflam­matory Response
Inflam­mation- Goal is to clean debris­/ba­cteria and prevent infection
Prolif­erative Phase
granul­ation, epithe­lia­liz­ation (the active growth phase). Goal is recons­tru­cti­on/scar tissue formation
Maturation Phase
recons­tru­ctive phase- goal is to remodel
 

Factors Influe­ncing Wound Healing

Diabetes
Poor circul­ation which slows down the blood which makes it harder to deliver nutrients to wound.
 
Decreased production of new blood vessels growth and healing hormones
 
Glucose in blood and urine is energy source for bacteria (leads to infect­ions)
 
Depression of the antiox­idant system and humoral immunity (leads to infect­ions)
 
Neurop­athy. They cannot feel pain so they won't know if a wound is getting worse/­inf­ected.
 
Elevated glucose levels decrease the functi­oning of red blood cells carrying nutrients to the injured area and limit the effect­iveness of white blood cells fighting infect­ions.
 
The inflam­mation stage frequently lasts too long and the wound can become chronic. In chronic wounds, the balance between producing and degrading collagen is lost and the wounds don't heal.
Nutrition, perfusion, immune status, infection, age
Wound Enviro­nment
wound type, size, location, type, depth
 

Wounds

Definition
A wound is a break in the continuity of soft tissues
 
Caused by a chemical, physical or biological insult
Types of Wounds
Incised, lacerated, penetr­ated, perfor­ating, punctured, gunshot, abrasion, avulsion, bite, ulcera­ting, granul­ating, septic­/as­eptic, closed
Aseptic = clean wound
septic = infected wound

Macrop­hages

-Critical cells because they secrete AGF
-Produce a host of cytokines and growth factors and act as chemoa­ttr­actants to the other cells needed for tissue repair
-Convert macrom­ole­cules to amino acid and sugars necessary for wound healing
-Bring in contra­ctual cells to encourage wound contra­ction
 

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