Wound Healing

PT 821 lecture 1

Why do PTs need a comprehensive understanding of the skin’s healing process?

to be able to make informed decisions about therapeutic interventions

What is the goal of the inflammatory process?

to reestablish homeostasis

What are the classically defined stages of wound healing?

• Inflammatory phase (days 1-10)

• Proliferative phase (days 3-20)

• Remodeling phase (days 9+)

T/F: the phases of wound healing are discrete and one phase does not begin until the previous stage is complete

FALSE there is frequently overlap between these phases

What factors may influence the degree to which wound healing phases overlap?

shape & severity of the wound

What factors influence the length of time of each phase of wound healing?

severity of the wound, comorbidities

During the _____ phase, it is critical to avoid disruption of the healing tissues

proliferative

Connective tissue is comprised of what three major components?

• Cellular elements

• fibrous elements

• ground substance

These cellular elements migrate through healthy tissue and collect at the site of tissue injury.

• fibroblasts

• fibrocytes

• myofibroblasts

• lymphocytes

• macrophages

• mast cells

• keratinocytes

• platelets and other specialized cells

Fibroblasts:

baby cells from which structure is derived

Fibrocytes:

matured fibroblasts

Myofibroblasts:

contractile fibroblasts; play a major role in wound closure

Lymphocytes:

found in both lymph and blood

Macrophages:

phagocytize dead tissue; clean up wound sites

mast cells:

release histamines; located @ base of blood vessels

keratinocytes:

major skin cells which strengthen the skin

What are the fibrous elements of connective tissue?

• collagen

• elastin

• reticulin

Collagen:

most abundant component of connective tissue; required to close and heal wounds; extremely strong

Elastin:

adds elasticity to tissue; important for scar formation to prevent excessive stiffness

Reticulin

a type of collagen (type III) that forms a delicate meshwork in connective tissue, providing structural support to various organs and tissues

Ground substance qualities

• surrounds cells and fibers

• clear, viscous, colorless

• Viscosity is temperature dependent

Why is the viscosity of ground substance important in wound healing?

too viscous: bacteria can linger and fester

not viscous enough: fluid moves past the wound too rapidly, preventing other cells from adequately performing their roles in the healing process

just right: bacteria can be more easily caught when ground substance is the optimal thickness, and other cellular elements can perform their duties as required while still allowing optimal flow of fluid at the site of the wound.

Describe the vascular reactions to tissue injury that occur in the inflammatory phase.

• Vasoconstriction

• Vasodilation

• Edema

• Necrosis

How and why does vasoconstriction occur within the context of tissue injury?

Platelets release serotonin, which induces vasoconstriction and helps to control pain and bleeding. This response allows time for other cellular elements to accumulate and respond to the tissue damage.

What chemical mediator stimulates vasodilation?

histamine (helps cells become more permeable)

Increased fluid near the site of a wound due to vasodilation results in what?

edema

What chemical mediator influences edema?

prostaglandins; impact blood flow and signal regeneration

At what point in the inflammatory process does necrosis occur?

throughout

What cellular element is associated with necrosis?

macrophages - clean up dead tissues/cells

When tissue injury occurs, what cells rush to the wound site?

• granulocytes - polymorphonuclear leukocytes (PMNLs)

• erythrocytes

• leukocytes

• platelets

• plasma protein

• lymphocytes

Macrophages comprise approximately ____ of all circulating ____.

65%, WBCs (white blood cells)

What may occur as a result of the inflammatory process in response to tissue injury?

lymph nodes may swell

What phrase forms the basis of treatment planning in the inflammatory phase?

If it is infection, get rid of the pathogen; if it is inflammation, stop disrupting (via cleansing, etc)

What begins during the proliferative stage of wound healing?

repair; wound closure

Fibroplasia:

creation of fibroblasts, maturation of fibrocytes and myofibroblasts

Fibroblasts follow _____ to the wound site.

macrophages

What type of cells attract endothelial cells?

myofibroblasts

These cells form new blood vessels

endothelial cells

These cells form new skin cells

epithelial cells

T/F: endothelial and epithelial cells do not form during the inflammatory phase

TRUE

Angiogenesis

result of endothelial cells forming new capillaries. New capillaries perfuse the collagen matrix, which provides a base for epithelial cell migration.

Granulation

a tissue which is highly vascularized with capillaries and consists primarily of macrophages, fibroblasts, and endothelial cells; all embedded in a matrix of fibronectin, proteoglycans, hyaluronic acid and collagen

What does healthy granulate tissue look like?

red and bloody

Revascularization only occurs over what type of tissue?

granulated tissue

Qualities of revascularization

• occurs only over granulated tissues

• budding and anastomosis toward areas without blood flow

• lymph vessels also form nearby

• essential to wound healing

Wound closure does not equate to :

wound healing!

T/F: wounds cannot close unless they are also healed

FALSE; wounds can close without healing and this is often an indication of poor wound healing

Three types of wound closure

1. Primary intention

2. Secondary intention

3. Tertiary intentino

Primary intention

surgeon closes a wound manually by approximating the edges with glue, staples, stiches, etc

Secondary intention

• two types: contraction and re-epithelialization

• wound is left open to close on its own, typically because its edges cannot be manually approximated

Tertiary intention

• healing by secondary intention, closed surgically

• typically occurs as the result of an infection or some other issue that has caused the wound to dehisce

Dehiscence

a wound closed by primary intention that later opens up again due to maceration or infection

What are the two types of secondary intention?

1. contraction

2. re-epithelialization

Contraction

• type of secondary intention

• peri-wound tissue moves toward center of wound

• myofibroblast activity

• can occur in infected or unprepared tissue

• the deeper the wound, the more likely it is to close by contraction because it is a faster process than re-epithelialization

Re-epithelialization

• can only occur over healthy granulated tissue

• begins within hours of wounding

• four step process

What are the four steps of re-epithelialization?

1. Mobilization

2. Migration

3. Proliferation

4. Differentiation

What are some examples of things that can interfere with re-epithelialization?

• presence of eschar

• dry environment

• too much cleansing

• toxicity

• confused cellular messaging (premature scar formation)

Which method of secondary intention is faster?

contraction

What secondary intention type is likely in a wound that is relatively deep?

contraction

What is contact inhibition?

when new epithelial cells meet in the middle of a wound, contact inhibition occurs to prevent continuous upward growth

When wounds heal, they are primarily comprised of _____. What implications does this fact have for deeper wounds?

Collagen
Different tissue types do not return to their pre-wounded state; adipose, muscle, and dermis tissue are not replaced with like tissues and the scar formed is weaker than the original tissue

Scar maturation or Phase three of wound healing occurs roughly during what timeframe?

9 days to 2 years post wound