Introduction to Wound Healing

A blood clot will soon dessicate to a scab, what are the three functions of a scab?

1. Protects from contamination 2. Maintains internal homeostasis 3. Provides surface under which epithelial cell migration and contraction can occur

What are the five roles of macrophages in wound healing?

1. Removal of bacteria and debris 2. Growth factor synthesis and secretion 3. Recruitment of mesenchymal cells 4. stimulation of angiogenesis 5. modulate matrix production

What is the the purpose of the inflammatory stage of wound healing?

Inflammation is essential to initiate the repair process and protect against infection.

What surfaces do not support granulation?

Intact surfaces (periosteum, fascia, tendon, nerve sheath)

When do neutrophil numbers in a wound reach their peak?

Neutrophils enter a wound areound 6 hours and reach their peak within 1-2 days after injury.

When do monocytes enter the wound?

~12 hours after the initial injury, They will become macrophages in the wound at ~24-48 hours

Give an example of a host factor

- age - nutritional status - hydration - renal disease/ hepatic disease - diabetes - obesity - species

True or False, Fibroplasia doesn't begin until the inflammatory stage is completely over.

*False* The proliferative phase of healing comes just as the inflammation subsides but before it totally resolves.

________________ are not required for non-infected wound healing whereas _______________ are required in all wound healing.

*Neutrophils* are not required for non infected wound healing whereas *Macrophages* are required in ALL wound healing.

True or False, epithelialization will occur under a scab?

*True* An occlusive or semiocclusive bandage can be used to increase humidity if there is no scab.

What is the process that occurs after the initial hemorrhage of a wound?

- A wound will initially bleed - The reaction of the damaged blood vessel is to constrict for 5-10 minutes to limit further hemorrhage. - Vasoconstriction is followed by vasodilation so inflammatory mediators can enter the tissues

Give an example of a wound factor

- exposed tissue - foreign material -mechanical trauma - blood supply -moisture - temperature - communication with synovial spaces - biofilm

Give an example of an external factor

- radiation therapy - chemotherapy - steroids - duration of anesthesia

Debridement is primarily characterized by what two cell types entering the wound?

1. Neutrophils 2. Macrophages

What are the four steps of angiogenesis?

1. Augmented microvascular permeability 2. release of proteinases from activated endothelial cells that in turn degrade the basement membrane around the existing vessel 3. migration and sprouting of new endothelial cells (capillary buds) 4. endothelial cell proliferation

Macrophages are key to reparation of the tissue because of their synthesis and secretion of what four growth factors?

1. Platelet derived growth factor 2. Transforming growth factor alpha and beta 3. Fibroblast growth factor 4. Interleukin-1

What are the four purposes of a blood clot (fibrin) at the site of the wound?

1. Chemoattractant and Growth Factor release 2. Prevent additional hemorrhage 3. Act as a scaffold for future cell migration 4. Block lymphatics to prevent the spread of inflammation

What are the three processes of the repair stage?

1. Fibroplasia 2. Angiogenesis 3. Epithelialization

The late inflammatory stage overlaps with the debridement stage - what three things occur in the late inflammatory reaction?

1. Fluid enters the wound to dilute toxic substances 2. Aids movement of cells into the area 3. Activated platelets release chemoattractants leading to diapedesis

What are the five signals for the fibroblasts to migrate and proliferate?

1. IL 1 2. Transforming GF-a and B 3. Platelet derived GF 4. Epidermal GF 5. Fibroblast GF

What are the four stages of Wound Healing?

1. Inflammation (0-3 days) 2. Debridement (0-3 days) 3. Repair (2-5 days) 4. Maturation (days - years)

What are the three phases of Wound Contraction?

1. Lag phase - increase in wound size 2. Rapid contraction - up to 0.8 mm/day 3. slow contraction - as wound becomes fully epithelialized

What are the three elements of granulation tissue?

1. Macrophages 2. Fibroblasts 3. New blood vessels

What is the role of the neutrophil in fighting bacteria and debris in a wound?

1. To seek and destroy destroy debris and bacteria via phagocytosis, and subsequent degradation with enzymes and oxygen-radical mechanisms.

Wound contraction will stop in what three situations?

1. Wound edges meet (contact inhibition) 2. excessive tension on the wound 3. a low myofibroblast development or function

What are the three broad categories that can affect healing?

1. Wound factors 2. Host factors 3. External factors

What are the four functions of skin?

1. protects organism from foreign material 2. Protects against organisms 3. homeostasis (water loss, heat) 4. Protects internal organs

What are the three components of matrix remodelling?

1. rapid collagen accumulation followed by Collagenolysis/synthesis to dissolve any non functional fibers 2. replacement of Type III with Type I 3. Gradual increase in strength

What are the two components of maturation?

1. wound contraction 2. matrix remodelling

What level of bacterial contamination causes infection?

>10^5 L

A wound that is fully matured will always be ________ weaker than normal tissue?

15-20%

At what rate does epithelization occur?

1mm/day from the wound edge

At 21 days a wound is only _____% of the strength of normal tissue?

20%

What is the normal skin ratio of type 1 to type 3 collagen fibers?

4:1

Define First Intention Wound Healing:

A clean surgical cut where appositional skin is brought together by suture and healed into a hairline scar

Define Second Intention Wound Healing?

A gaping irregular wound that you let granulate and heal over on its own

Define Third Intention Wound Healing

A wound you allow to granulate initially, then after a certain period of time you suture it closed. The suture line is not as clean as first intention but there is less scarring than second intention.

When does maturation occur?

After day 17

The repair stage is the third stage of wound healing and occurs at what time?

After day 2-5

Debridement is the second stage of wound repair, when does it occur?

Anytime in Day 0-3, often ~ 6 hours after the wound.

As collagen content ____________, fibroblast numbers _____________

As collagen content increases, fibroblast numbers decrease.

Why do large wounds heal slowly?

As epithelial migration gets further from the wound edge it dwindles to a monolayer and progresses slowly.

Why is there a delay of 4-6 days before new epithelium is seen?

Because it needs a granulation bed to migrate across (this delay doesn't occur in first intention wounds)

What is Angiogenesis?

Capillary Infiltration - new capillaries follow the fibroblasts.

Define contact inhibition:

Contact inhibition dictates when epithelial migration is complete - cells will stop when they contact one another on all sides.

Who heals better Cats or Dogs?

Dogs, Sutured wounds in cats are 1/2 as strong after 7 days as in dogs.

What is fibroplasia?

Fibroplasia is characterized by the infiltration of fibroblasts into the wound.

What is epithelialization?

Formation of new skin

What is the purpose of granulation tissue?

Granulation tissue replaces the fibrin containing clot and acts as a physical barrier to infection while providing a surface for the cells to migrate across.

When is granulation tissue deposited?

Granulation tissue will replace the fibrin containing clot during the repair stage (fibroblast proliferation & capillary infiltration)

What is the role of Growth Factors?

Growth factors initiate, maintain and coordinate formation of granulation tissue.

Describe the process of epithelialization:

Guided by collagen fibers, migrating epithelial cells enlarge, flatten and lose attachment to the underlying BM. They will extend broad pseudopodia over the exposed collagen surface. Cells will slide over altered cells until they contact the wound.

Immediately after a wound occurs there is hemorrhage, what is the purpose of this?

Hemorrhage will clean the wound bed

Inflammation as a stage of wound healing occurs when?

Immediately (day 0-3) Can be prolonged due to other factors

What stimulates angiogenesis?

Low O2 tension stimulates angiogenesis

What is the role of macrophages in wound healing?

Macrophages carry out the debridement, microbial killing, secretion of collagenases and coordination of later stages of repair via synthesis and secretion of cytokines.

How are macrophages 'recruited' to a wound?

Monocytes are recruited from the blood by platelets and neutrophils

Describe the process of wound contraction?

Myofibroblasts have a well developed alpha smooth muscle actin microfilamentous system that exerts tension on the ECM via integrins.

Define Pus:

Pus is the combination of wound fluid, tissue debris and neutrophils.

What is the goal of wound healing?

Restore an intact epithelial barrier

During what stage does a practitioner have the ability to exert the greatest influence on wound healing?

Stage 1: inflammation stage

When does epithelization occur?

Starts ~24 hours after wounding but it is not until 4-6 after wounding that new epithelium is seen as pink tissue around the edge.

Coagulation is triggered by what?

Thromboplastin released from injured cells

What happens to epidermal cells on the periphery of a wound?

basal epidermal cells at the wound margins undergo phenotypic alterations that favor mobility, migration and phagocytic activity. They will migrate across the wound.

_____________ are the cells responsible for contraction, they combine characteristics of __________ & ____________

myofibroblasts are the cells responsible for contraction, they combine characteristics of smooth muscle cells and fibroblasts.

Who heals better ponies or horses?

ponies Horses will have a prolonged inflammatory response and are more likely to have exuberant granulation tissue.