Wound Healing (including problems and treatments) Flashcards
What is wound healing?
Regeneration so that it returns to original purity
Induced by keratinocytes and endothelia
Only reptiles and amphibians can technically do this
What is wound repair?
Scars form so there is compromised functionality
Fibroblasts are responsible for this
Technically what we are calling “wound healing” when we talk about mammals
- except liver and fetal tissue can truly heal
What are the 4 stages of wound healing?
1) hemostasis*
2) inflammation*
3) repair (proliferation/granulation phase)
4) remodeling and scar formation
- hemostasis and inflammation have typically been lumped together for ones that say there are 3 stages because they both happen very quickly
What is the first thing that comes to the wound when it first forms?
Platelets
“activate and aggregate”
form the platelet plug
What is present at the end of the hemostasis phase of wound healing?
The fibrin clot
What is the primary initial recruiter of neutrophils to a wound?
Other neutrophils
What is a basic overview of what happens during the hemostasis phase of wound repair?
Occurs immediately to within hours of injury
Coagulation occurs forming a clot/scaffold
Recruits inflammatory cells
What is a basic overview of what happens during the inflammation phase of wound repair?
Should take minutes to 72 hours in healthy tissue
Immune infiltration
Debris clearance
Pathogen killing
What is a basic overview of what happens during the proliferation stage of wound repair?
2-10 days after injury
Fibroblast proliferation
Scar formation
Collagen synthesis
Angiogenesis
What is a basic overview of what happens during the remodeling stage of wound repair?
Within days to months
Epithelialization
EMC remodeling
Scar maturation and contraction
Apoptosis
What do injured/damaged cells produce that cause vasoconstriction (to stop hemorrhage) and then vasodilation (to get cells there)?
Histamine, serotonin, catecholamines
What is the primary activator of platelets?
Collagen (von Willebrand’s factor mediates linking of collagen and platelet)
What happens when platelets are activated?
They change shape to dendritic form
Release their granules (dense and alpha)
Release VWFs and thromboxane A2 –> help platelets stick
What are platelet dense granules?
Released by platelets
Have serotonin, adenosine diphosphate (ADP), and ATP
To help vasoconstriction and have platelets stay there
What are alpha granules?
Released by platelets
have fibronogen, fibronectin, PDGF, and P-selectin
What is the role of platelet-derived growth factor (PDGF) in wound healing?
Platelet is 1° source
Released from α granules
Function:
- Attract neutrophils & macrophages
- Initiates chemotaxis of smooth muscle cells & fibroblasts
- Stimulates contraction (platelet and macrophage, not fibroblast)
- Induce myofibroblast phenotype of fibroblasts
What is the role of transforming growth factor β1 (TGF-β1) in wound healing?
Platelets = most important storage factor
Elicits rapid chemotaxis of neutrophils & monocytes
Perpetuate inflammatory cell response
Intracellular signaling pathways
Adhesion molecules, coagulation factors, cytokines, GFs
Stimulates fibroblast contraction
Stimulates myofibroblast differentiation
Stimulate fibroblasts to produce hyaluronan (HA) and RHAMM ( its receptor)
What are the intrinsic factors in the coagulation cascade?
“For intrinsic factors if it not $12, but $11.98”
Factor XII –> factor XI –> factor IX
What are the common factors in the coagulation cascade?
“small change”
Factor X and factor I
What does thrombin do?
aka factor IIa
activating platelets
activating factors V, VIII, and IX
What are the functions of the fibrin clot?
Hemostasis
Microorganism barrier
Matrix scaffold for cell attachment
Growth factor reservoir (PDGF and TGF)
What is involved in clot-lysis?
Limit platelet aggregation & clot formation
Plasminogen activator
- Initiates clot lysis
Anti-thrombin III (AT III)
Protein C
- Factors V and VIII
Prostacyclin C (PC)
- Limit platelet aggregation
What are the main roles of neutrophils in wound healing?
Debridement and phagocytize
- necrotic debris
- microbes
- foreign material
Produce critical cytokines to recruit macrophages, fibroblasts and keratinocytes
When done they undergo effete/apoptosis
- remove with eschar or phagocytized by macrophages
What are the chemoattractants involved in neutrophil chemotaxis during wound healing?
IL-8, Gro, Kallikrein, FDPs, Fibrinopeptides, bacterial proteins, platelet released cytokines
What is diapedesis?
Immune cell going from blood vessel to outside of it
Facilitated by CD11/CD18 integrins adhering to endothelial I-CAM
What is the role of macrophages in wound healing?
Within 24-48 hours, become predominant
* Transition between inflammation & repair
Phagocytosis, killing bateria, clean up debris
Removal of effete (inactive/useless) neuts
Release GF (growth factor) and recruit and activate fibroblasts
- PDGF, FGF (fibroblast growth factor), TGFB1
Then are removed via apoptosis
What are M1 macrophages?
Traditional ones that phagocytize
What are M2 macrophages?
Aid in immune suppression and tissue repair
What induces macrophages to be M1 macrophages?
IFN-y
LPS
TNF-a
What induces macrophages to be M2 macrophages?
IL-4
IL-13
IL-10
TGF-b
What cells play a role in the repair phase of wound healing?
Macrophages
Fibrocytes
Endothelial cells
Keratinocytes
Which mediators play a role in the repair phase of wound healing?
Integrins
Growth Factors
Enzymes
Serine proteases
MMP’s
What is granulation tissue?
Occurs 3-5 days post injury in healthy wound
Functions as rudimentary tissue (2nd provisional matrix)
Grows until wound bed is covered
Consists of: new blood vessels, fibroblasts, inflammatory cells, endothelial cells, myofibroblasts, new ECM components (fibronectin, hyaluronan)
Lots of GAGS so cells can slide over each other
What happens to a fibroblast that experiences mechanical stress and/or is exposed to TGF-b?
It becomes a proto-myofibroblast –> myofibroblast
- now they can contract
- increases production of cytokines, collagen, and HA
Which cells store the most TGF-b1?
Platelets
What type of collagen is present in granulation tissue?
Type III (very thick so can easily be packed on!)
become type I (thinner) over remodeling phase
What type of collagen is found in vessels and hypertrophic scars?
Type V
What happens in wound contraction?
Fibroblasts contact simultaneously and equally across wound
Centripetal/concentric decreases in size of open wound
Degree of contraction
- Full thickness will contract up to 40%
- Partial thickness will contract less (due to adnexa)
Peaks at 2 weeks
Inhibited by:
- Excessive tension
- Necrotic tissue
What happens in the angiogenesis/neovascularization process?
Initiated by endothelial cells near wound
Starts 2 days post-injury
Proteinases (MMPs) break down
- Mature blood vessels
- ECM –> release stored growth factors
Stimulated by macrophage-released cytokines, decreased O2, lactic acid & GFs
What does Vascular Endothelial GF (VEGF) do during wound healing?
Stimulates angiogenesis
Induces neovascularization
Induces synthesis of MMPs
What does Basic Fibroblast GF (bFGF) do during wound healing?
Stimulates angiogenesis
What do keratinocytes need for proper re-epithelialization if there is no basement membrane?
Moist bed of granulation tissue
What is lamellipodia?
Maybe triggered by low calcium and high magnesium
Keratinocytes start moving via integrins
Can “leap frog” over each other
Can migrate over healthy granulation tissue (collagen, fibronectin, fibrin)
Cannot migrate over intact basement membrane
What is the tensile strength (compared to original) of the skin during healing?
3 weeks = 20%
1 month = 30%
Final = 70-80%
What triggers the extrinsic pathway of coagulation? Then what happens?
injury to the endothelial tissue (i.e., skin tissue)
–> exposes tissue factor (factor III) to the blood
Factor III then binds with Ca2+ and Factor VIIa to activate Factor X
What triggers the intrinsic pathway of coagulation? Then what happens?
Factor XII is exposed to collagen or bradykinin and is activated
XIIa activates XI –> XIa activates IX –> IXa combines with VIIIa and Ca2+ to activate X
What activates the common pathway? Then what happens?
After the activation of factor X at the end of either intrinsic or extrinsic pathway
Xa, Va and Ca2+ bind together
–> activate II (prothrombin) into IIa (thrombin)
–> activates I (fibrinogen) into I (fibrin)
–> fibrin binds to XII and Ca2+ to stabilize the clot
What is von Willebrand factor?
A glycoprotein that binds to factor VIII and protects it from breaking down
also helps with platelet and collagen adhesion
What is the role of complement in wound healing?
anaphylotoxins released (C3a, C5a)
- Increased vessel permeability, attracts neuts and monocytes to site
- Trigger release of vasoactive amines (histamine, LTC4, LTD4) from mast cell
What is the role of mast cells in wound healing?
In all phases except the clot
Still discovering their full function (mast cell knockouts still heal)
Degranulate when exposed to C3a and C5a
- Release: TGF-B1 – important trigger
Exposed to type III collagen (when the fibrin clot is formed) and fibronectin
- Release: chymase, tryptase
o These break down the ECM to allow new cells to come in including collagen I
Interact with fibroblasts and myofibroblasts (wound contraction)
What are migration promotors for keratinocytes?
touching the provisional matrix
TGF-B
EGF (epith growth factor)
Fibronectin
collagen VI
What keratins do new, migrating keratinocytes express during re-epithelialization?
Express K5/14 as well as K6/16
What are chemoattractants for endothelial cells?
Released from keratinocytes nearby:
- VEGF (vascular endothelial growth factor) also called VPF
- TGF-a
Released by degraded ECM: fibronectin
Released from mast cells: heparin
What is the most important growth factor for neovascularization?
FGF
Released by macrophages and platelets
How does FGF promote neovascularization?
–> endothelial release of plasminogen activator, procollagenase
–> activates MMPs
–> degrade basement membrane of current vessel
–> allows migration of endothelial cells
Do the stages of wound healing progress in a linear pattern?
Not completely, many things overlap and are happening at the same time
What is the fibrin clot?
First extracellular matrix that forms!
Derived from fibrinogen and interacts with platelets to form clots
Fibrin acts with PDGF to make fibroblasts express fibronectins
- Fibronectin deposition results in lysis of clot
What is fibronectin?
Second extracellular matrix – deposited by fibroblasts
Has many functions in tissues, blood
Binds fibrin, supports fibroblasts, keratinocytes and endothelial cell adhesion
Opsonizes ECM debris to clean it up
Forms template for collagen
What are keloids?
fibroproliferative disorder (scar above wound bed and invades normal tissue)
- in humans, African-Americans are predisposed
- “proud flesh” in horses is similar to this
Abnormal wound healing response (problem with proliferation)
- excessive and prolonged deposition of collagen (esp III)
- no myofibroblasts
share several features with hypertrophic scars
What is the inflammatory response like in dogs versus horses?
Dogs have a quick inflammatory response but in horses it is weak and prolonged
What is the predominant collagen type in mature scar tissue?
Collagen I
What is granulation tissue like in a dog versus a cat?
Dog:
- Begins at center
- Cover all
- Forms 7.5 days
- more direct cutaneous vessels
Cat:
- Begins at periphery
- Delayed collagen production
- Forms 19 days
- “pseudohealing” = looks healed from the outside but the collagen isn’t there yet
What do the letters stand for in the TIME wound healing evaluation model?
T = are there any necrotic/non-viable tissues
I = is there inappropriate inflammation (lasting beyond 3 days) or infection
M = is there too little or too much moisture
E = monitoring epithelialization
What are hypertrophic scars?
contained within the site of injury and may regress over time
problems occur in the remodeling phase
Widely spaced collagen
Abundance of myofibroblast
What is exuberant granulation tissue aka proud flesh in horses?
Similar to keloids but occur before re-epithelialization
- wound margins may display a hyperplastic epidermis
- ulceration of the central portion of the wound is common
More common on limbs
TGF–B1 activity is increased
May have mast cell hyperplasia
Steroids can decrease excess inflammation and slow fibroblasts
- but also slows epithelialization and continues problem
What is the role of mast cells in wound healing?
They should not have much of one
More prominent if something goes wrong
What is a diabetic ulcer?
Can occur in dogs in addition to humans
- Chronic non-healing wound
- Stuck in proliferative phase with excess ECM
- Reduced MMPs due to hyperglycemia
- Macrophages don’t release cytokines like they should
In cats diabetes can cause skin fragility syndrome potentially due to microvascular complications from high blood sugar levels
What are decubitus ulcers/wounds?
Prolonged pressure over bony eminence, compress capillary circulation and cause tissue damage/necrosis
Graded from I to IV
I – epidermis and superficial dermis
*II – subcutis
*III – deep fascia
*IV – underlying bone
*require surgery
What is the primary objective in the management of any wound?
reduce the number of contaminants that may interfere with the healing process
- foreign material
- nonviable tissue
- microorganisms
- cellular exudates
What are abrasion wounds?
Partial thickness skin loss from:
- shearing forces (friction)
- contusion (blunt trauma)
contamination is common (e.g. with bacteria, devitalised tissue and debris)
Consider: thorough cleansing and debridement; second intention healing.
What are avulsion wounds?
Deep abrasion with:
- tissue tearing (anatomical avulsion)
- detachment (physiological avulsion; degloving)
- Common with vehicular trauma and affecting distal limbs
Extent of injury may be underestimated and contamination is common
Consider: systemic assessment; repeated surgical and/or selective debridement; use of NPWT
What are burn wounds?
Injury to the skin or other tissue caused by:
- heat
- radiation
- radioactivity
- electricity
- friction
- contact with chemicals
Severity based on the size and depth of the burn
Severe deep burns (>20% body surface) are associated with major metabolic derangements and require intensive care
7–10 days to visualize the interface between eschar and viable tissue
high risk of wound infection and sepsis, scarring and wound contracture
Consider: aggressive early systemic management and nutrition; early debridement when feasible; need for final wound reconstruction or use of skin substitutes.
What are non-selective strategies of wound debridement?
- Irrigation (no evidence for sterile fluids over tap water +/- surfactants)
- Surgical (fastest and most efficient)
- Mechanical (ex. wet-to-dry dressing)
What are selective strategies of wound debridement?
- biological (ex. maggots)
- enzymatic (ex. collagenase ointment)
- autolytic (ex. via use of active dressings)
How long after injury should any wound which has not already been treated be considered contaminated?
3-6 h
What is biofilm?
when multispecies bacterial com-munities organize onto a wound surface and form an extracellular matrix of polysaccharides, proteins and nucleic acids to provide protection and ensure survival
What kind of debridement is recommended when there is a biofilm?
Frequent sharp wound debridement to physically remove the biofilm
How do antibiotics and antiseptics differ?
Antibiotics have a specific mechanism of action that often interferes with a specific component of the bacterial replication or metabolism
Antiseptics have a more general mechanism of action that kills bacteria through direct chemical destruction
Which common, historical antiseptics have been proven to be cytotoxic and interfere with the host’s natural immune response?
hydrogen peroxide
Dakin’s solution (dilute bleach)
chlorhexidine
- in vitro even with very dilute concentrations
- in vivo did not significantly delay healing time
Which antiseptics have fair to excellent evidence for use in wounds and have fair to excellent tissue compatibility?
Polyhexanide (contact time of 10–15 min)
Octenidine (only needs 1 min contact, not for deep wounds/punctures)
Hypochlorous acid (good for sensitive tissue)
Iodine
Nanocrystalline silver (prophylactic use not recommended)
Honey
How is hypochlorous acid different from sodium hypochlorite?
hypochlorous acid = super-oxidized water
- is produced by the electrolysis of water and NaCl to generate ROS
- stabilized and pH-neutralized
- not cytotoxic
sodium hypochlorite = bleach
How is silver used in wound care?
is directly toxic to multiple components of the bacterial cell
- high concentrations of silver ion can cause host cytotoxicity
Scientific literature no longer supports (SSD) on any wounds or burns
- slows healing
Nanocrystalline silver for early treatment phase of infected wound (2-3 wk)
- no evidence that it is helpful at preventing infection
- may delay epithelialization
How is honey used in wound care?
Use during inflammatory & repair phase
- promotes healing of all wound types (including burns)
Debridement
Hyperosmotic effects due to hypertonicity
- dehydrates bacteria
- promoting lymphatic flow –> reduces tissues edema
Anti-inflammatory effect and stimulates proliferation of fibroblasts
- stimulates granulation tissue
Multiple antibacterial effects
- but may not be enough in critically contaminated or infected wounds
How is granulated sugar used in wound care?
creates a hypertonic environment like honey
lacks the antibacterial and anti-inflammatory effects of honey
can be painful during bandages changes
but is a cheaper alternative to medical grade honey
How is fish skin used in wound care?
Usually tilapia/cod
Has excellent skin adherence
Induces growth factors
- EGF
- FGF
Has antimicrobial activity
May cause suboptimal cosmetic results (discolored and scarred skin)
What is bandaging?
Usually is 3 layers
Are often placed over dressings to protect them, absorb excess fluid, and hold them in place
Can control swelling and facilitate immobilization
What is a wound dressing?
Any material that is applied directly to a wound with the intention to protect it and, in the case of modern dressings, promote healing
A good dressing:
- Creates a moist environment
- Is a physical barrier
- Occludes dead space
- Allows for atraumatic removal
- Is easy to manipulate
- Is nonantigenic, nonallergenic, and sterile
Can be synthetic, semi-synthetic, or biologic
What happens in a dry wound microenvironment?
Loss of extracellular fluid
Need for scab formation/breakdown to recreate the moist environment
Waste of time and energy
Prolonged healing time
*created by traditional dressing (ex. cotton/gauze)
What happens in a moist wound microenvironment?
Correct amount of moisture
Promotion of autolytic debridement, granulation tissue, and epithelization
Decreased inflammation and preservation of growth factors
Decreased infection
Decreased pain and scarring
*created by semi-occlusive dressings
What happens in a wet wound microenvironment?
Presence of an impermeable membrane around entire wound that allows for delivery of analgesics, antimicrobials, bioactive molecules (e.g. growth factors), and micrografts
Wound edge maceration and promotion of infection
*created by occlusive dressings which are rarely used
What are some commonly used active (non-biologic) wound dressings?
Films
Foams
Hydrogels
Hydrocolloids
Alginates
*usually contraindicated in dry, infected, or necrotic, or highly exudative wounds
What are some commonly used biologically active wound dressings?
Natural biomaterials (ex. collagen, gelatin, hyaluronic acid)
Bioactive glass fibers
Acellular matrix based (ex. intestinal submucosa, pericardium)
Combination matrix based wound products (ex. collagen + MMP inhibitor)
Platelet rich plasma (contains cytokines and growth factors)
What is the goal of biologically active wound dressings?
may promote physiological repair at the molecular level through various mechanisms, including the use of biomaterials used as 3D scaffolds and the inclusion of live cells or other bioactive ingredients such as growth factors
What is negative pressure wound therapy (NPWT)?
accelerate wound healing through a continuous partial vacuum
- increases the speed of granulation tissue formation
- decreases the total time for wound closure
- mechanisms are probably multifactorial
–> increased tissue perfusion
–> reduced edema
–> accelerated angiogenesis through deformation of the wound bed
–> removal of wound exudates (detrimental cytokines, proteases)
When is negative pressure wound therapy (NPWT) contraindicated?
Exsanguination
Neoplasia
Necrotic tissue/eschar
What is hyperbaric oxygen therapy (HBOT)?
use of oxygen under pressure delivered in a specialized chamber
- increase in the oxygen carrying capacity of the blood –> higher perfusion
- chronic non-healing wounds are frequently hypoxic (poor perfusion)
- increases leukocyte oxidative killing capacity
- modulates of nitric oxide production
- modifies growth factors and cytokine effects
- decreases vasogenic edema
- is synergistic with many antibiotics and antifungals
Used for many conditions
Complications include barotrauma, cataracts, dyspnea and seizures
Contraindications: pneumothorax, pulmonary disease, thoracic or ear surgery, fever, pregnancy, comatose/unconscious patients, seizures
What is Partial Thromboplastin Time (PTT)?
evaluates the intrinsic and common pathways of the coagulation cascade
What is indicated by a Prothrombin Time (PT)?
problems with fibrinogen, factor V, VII, X, and prothrombin
may indicate liver disease, vitamin K deficiency, or the presence of anticoagulants
What is Prothrombin Time (PT)?
measures the time it takes for blood to clot
primarily assesses the extrinsic pathway of the coagulation cascade
What is indicated by a Partial Thromboplastin Time (PTT)?
problems with factors such as VIII, IX, XI, and XII, as well as fibrinogen
deficiencies in these clotting factors, hemophilia, or the presence of inhibitors
