2B - Wound Healing Models

wound that heals in timely fashion

acute wound

slow to heal

“Wound that have failed to proceed through an orderly and timely process to produce an anatomic and function integrity” – Wound Healing Society

chronic wound

Healing rate affected by:

depth, location, cause of wound, patient age, physical condition etc..

medicare says longer than ___ days to be acute

30

_____ phase = 24 – 48 hrs

acute inflammatory → innate

_____ phase = 2-10 days

subacute inflammatory → acquired + innate

_____ phase = 2-20 days

proliferative

_____ phase = 9 days - up to 2 years

remodeling

what is another name for neutrophils?

polymorphonuclear cells

what are the chemical mediators of inflammation?

• histamine

• leukotrienes

• prostaglandins

• bradykinin

what are the 3 steps to the inflammatory phase?

1. Vascular response to injury

2. Cellular response to injury

3. Chemical mediators of inflammation

what are the hemostatic mechanisms in the inflammatory stage?

• curtail blood flow

• reduce oxygen delivery to wound

• produces hypoxia

what is the key signal to control wound healing?

HYPOXIA

why is hypoxia a key signal in wound healing?

recruits endothelial cells and facilitates angiogenesis in repair phase

local hypoxia causes what processes?

• shift to anaerobic glycolysis

• increases lactate production

• activates angiogenesis and collagen synthesis

wound space becomes ___ and ___ after hypoxic processes take place

hyperlactive and acidotic

what are the platelets role in vasoconstriction in the inflammatory phase?

• first to arrive → activate, adhere, aggregate

• release serotonin

• release PDGF

what is PDGF? function?

platelet derived growth factor

chemotaxis (calls in) neutrophils and macrophages

purpose of serotonin in wound healing? what releases it?

vasoconstrictor

platelets

what is the purpose of vasoconstriction in the inflammatory response?

seals injured area, delays bacterial invasion

brief arteriolar vasoconstriction to restrict blood flow, followed by ____

vasodilation

what triggers the immune response? (concerning wounds)

damaged tissue

what is mast cell degranulation?

when mast cells release inflammatory substances into circulation

what is the purpose of vasodilation in the inflammatory stage?

• release of chemical triggers → histamine, prostaglandins, leukotrienes

• opens microvascular beds

opening of microvascular beds allow what to happen?

Increased heat, redness, cellular mediators

Increased intravascular pressure - early transudate into interstitium

what are the components of the vascular response to injury?

vasoconstriction, followed by vasodilation

what are the polymorphonuclear leucocytes from the blood included in the cellular response?

• neutrophils

• eosinophils

• basophils

• mast cells

neutrophils proliferate in what type of environment?

hypoxic acidotic environment

neutrophils produce ____ to fight bacteria

superoxide

neutrophils mostly are phagocytic of what type of cell?

granulocytes

neutrophils secrete ____ and ____ to hydrolyze necrotic tissue

proteases; collagenases

accumulation of dead neutrophils that have phagocytized debris in wound

pus

T/F Neutrophils have a short lifespan

true

at what stage does pus come from the wound?

inflammatory → cellular response

function of eosinophils in the cellular response of the inflammatory phase

modulate allergic inflammatory response, kill parasites

function of basophils in the cellular response of the inflammatory phase

Release histamine & heparin

function of mast cells in the cellular response of the inflammatory phase

• chemotactic factor for leucocytes and macrophages

• release histamine

• release heparin which stimulates migration of endothelial cells

• heparin also accelerates the activity of leukocyte phagocytosis

function of neutrophils in the cellular response of the inflammatory phase

• proliferate in hypoxic acidotic environment

• most phagocytic of granulocytes

• Produce superoxide to fight bacteria

• Secrete proteases and collagenases to hydrolyze necrotic tissue

• Wound pours forth pus

• Short lifespan

the release of heparin stimulates the migration of ____ cells

endothelial cells

difference between endothelial and epithelial cells

epi- barrier on body surfaces and line internal organs

endo- specialized epithelial cell, line the inner surfaces of blood lymphatic vessels

heparin also accelerates the activity of what?

leukocyte phagocytosis

what is the process of leukocyte emigration?

1. margination and rolling

2. adhesion

3. transmigration (diapedesis)

4. chemotaxis and activation

what is the most important regulatory cell type in the cellular response of the inflammatory stage?

macrophages

function of macrophages in the cellular response of the inflammatory stage?

• Differentiate from monocytes when they leave bloodstream

• Large phagocytic cell that can ingest large microorganisms & debris

• Excretes ascorbic acid, hydrogen peroxide leading to more macrophage recruitment (prolonging inflammatory response)

• Tolerate severe hypoxia and acidotic environment

• Attracts fibroblasts, endothelial cells and vascular smooth muscle cells

• Essential for the transition between inflammatory and repair phases

macrophages differentiate from _____ when they leave the _____

monocytes; bloodstream

Large phagocytic cell that can ingest large microorganisms & debris

Essential for the transition between inflammatory and repair phases

Transcend all phases of wound healing

macrophages

macrophages excretes ____ ___ and _____ ____ leading to more macrophage recruitment → prolonging inflammatory response

ascorbic acid and hydrogen peroxide

macrophages attract what type of cells to the injury site?

fibroblasts, endothelial cells, and vascular smooth muscle cells

what is AGF?

angiogenesis growth factor

what does AGF do?

stimulates budding of endothelial cells from damaged blood vessels

macrophages are chemotactic for ____ during late stages of inflammatory phase

fibroblasts

M2 microphages can activate what type of cells?

FAP = fibro-adipogenic progenitor cell

what lymphocytes are released in the cellular response of the inflammatory stage?

• B & T Lymphocytes

• Helper B cells

• Suppressor B cells

lymphocytes are part of the ___ immune response

acquired

why are lymphocytes up-regulated so late?

because the lymph system is super slow

increased blood flow

rubor

fluid accumulation (plasma protein and blood cells)

tumor

increased blood flow to superficial tissues, histamine release

calor

chemical mediators, nerve compression? (pain is normal response)

Dolor

Functio laesa

loss of function, becomes very severe

Should you try to prevent acute or chronic inflammation?

want acute to start the process → enflamed tissue activates healing

do not want chronic to delay process → won’t let you move into the proliferative phase

what are the 3 steps of the proliferative phase?

1. Re-enforcement of injured tissue (fibroplasia)

2. Blood Supply (neovascularization)

3. Permeability Barrier (re-epithelialization

how do you know you’re in the proliferative phase?

• Presence of Fibroplasia → yellow slough

• Presence of pink granulation dots → neovascularization

• Contraction

• Endothelial cells → “white / pink crushed glass”

Most important cell in production of dermal matrix is the fibroblast → stimulated by low O2

fibroblasts

what is in the ECM during the proliferative phase?

Collagen, Fibronectin, Laminin → structural and metabolic support

Elastin → elastic properties

Hyaluronic acid → fibroblast proliferation

Cross-linkage welding together of the collagen matrix produces →

durability and tensile strength

the better the organization & cross-linkage, the better the →

tensile strength of the scar

why is scar tissue mobilization important?

allows for the tissue to return to normal function and not break apart as easily

what vitamin is important for cross-linkage?

vitamin C

Myofibroblasts contain ?

actin & myosin

myofibroblast function in the proliferative phase

• Differentiate from fibroblasts

• Contract & extend

• Draw the edges of the wound together

• Influence rate & amount of wound contraction

Proliferative Phase → neovascularization (proud flesh) steps

1. Angiogenesis (neovascularization)

2. Endothelial cells respond to AGF

3. Development of new blood vessels gives bright red appearance (granulation tissue)

4. pink, soft, granular appearance underneath wounds (fibroblasts and angiogenic tissues in ECM)

5. Provides matrix upon which epithelial cell migration occurs

What triggers endothelial cells to respond in angiogenesis?

AGFs secreted by macrophages and a hypoxic environment.

what is angiogenesis?

preexisting vessels send out capillary-like sprouts

What is the visual appearance of newly developed blood vessels in granulation tissue?

Bright red due to increased blood supply

How does granulation tissue appear under wounds?

Pink, soft, and granular due to the presence of fibroblasts and angiogenic tissues in the extracellular matrix (ECM).

What is the role of granulation tissue in wound healing?

provides a matrix for epithelial cell migration, aiding in tissue repair and regeneration.

Why does hypoxia stimulate angiogenesis?

low oxygen environment signals the need for new blood vessels to restore oxygen supply.

Proliferative Phase → re-epithelialization steps

1. Keratinocytes respond to epidermal defect by migrating from wound edges

2. Superficial wounds heal by reepitheliatlization

3. Epithelial Islands

4. Epithelial cells migrate towards center of wounds

5. Contact inhibition stops migration

6. Migration is O2 dependent (want high O2 levels)

How do keratinocytes respond to an epidermal defect?

migrate from the wound edges to cover the defect

How do superficial wounds heal?

By re-epithelialization, where new epithelial cells cover the wound

What are epithelial islands?

Clusters of epithelial cells lining skin appendages such as hair follicles and sweat glands, which contribute to wound healing.

in which direction do epithelial cells migrate during wound healing?

Toward the center of the wound.

What stops epithelial cell migration once the wound is covered?

Contact inhibition, where cells stop moving once they touch each other.

What environmental factor is essential for epithelial cell migration?

High oxygen (O₂) levels, as migration is oxygen-dependent.

What are the two migration patterns of keratinocytes during wound healing?

Leapfrog or train fashion, depending on wound depth.

In what type of wound environment do keratinocytes migrate best?

A moist wound environment

What happens when contact inhibition occurs during wound healing?

Migration stops, leading to curled or rolled wound edges

what is the 4 step process of re-epithelialization?

1. mobilization

2. migration

3. proliferation

4. differentiation

new skin is initially ___% strength of orifinal

15%

when new skin forms, it is ___& of original strength

70-80% → never gets back to 100%

Remodeling phase steps

1. Fibroblasts disappear

2. Collagenase

3. As wound mature collagen lysis increases

4. Too much O2 causes hypergranulation (synthesis is O2 dependent – lysis is not)

What happens to fibroblasts during the remodeling phase of wound healing?

Fibroblasts disappear as the wound matures.

What enzyme regulates fibroplasia by balancing collagen synthesis and lysis?

Collagenase

What happens to collagen lysis as a wound matures?

Collagen lysis increases to remodel the wound

How does oxygen affect collagen synthesis and lysis?

Collagen synthesis is O₂-dependent, but collagen lysis is not

What is a potential consequence of excessive oxygen levels in wound healing?

Hypergranulation, or excessive granulation tissue formation

Genetic inhibition of lysis, unbalanced synthesis and lysis of collagen

larger than original region of injury

keloid formation

what are the 3 Rs of a hypertrophic scar?

red, rigid, raised → prevents normal movement

what are the long list of causes of chronic inflammation?

Wound sealed by necrotic tissue

Presence of pathogens (critical colonization)

Foreign material that cannot be phagocytized

Inefficient cellular activity

Misuse of cytotoxic agents

Frequent irritation

Repeated trauma

Granuloma (fibroblasts produce large amount of collagen to surround foreign material)