Chapter 24: Wound Healing

Question 1

What are the phases of wound healing?

Answer 1

1. Inflammatory phase
2. Proliferative phase
3. Remodeling phase

Question 2

What occurs in the inflammatory phase of wound healing?

Answer 2

Platelets release growth factors to attach macrophages and neutrophils to the healing site. The goal of the stage is to remove debris, necrotic tissue, and bacteria from the wound

Question 3

What occurs in the proliferative phase of wound healing?

Answer 3

Two main outcomes:

1. Fibroblasts begin to produce collagen in a random fashion. The wound begins to gain initial strength.
2. Angiogenesis begins at the healing site

Question 4

What occurs in the remodeling phase of wound healing?

Answer 4

Randomly aligned collagen is replaced by organized collagen that provides stronger strength to the site

Question 5

What is the time frame of the inflammatory phase?

Answer 5

Begins at time of wound and lasts 24-48 hours

Question 6

What time frame is the proliferative phase?

Answer 6

Usually begins after 48 hours and lasts for approximately 2-3 weeks.

Question 7

What time frame is the remodeling phase?

Answer 7

Usually begins 2-3 weeks after injury and depending on severity can lasts several months to more than a year.

Question 8

What role do macrophages play in wound healing (2 main functions)

Answer 8

1. Removing debris and bacteria from site.

2. secrete growth factors that promote collagen formation by fibroblasts (most important function)

Question 9

What role does PDGF play in wound healing?

Answer 9

Platelet Derived Growth Factor is released by platelets during formation of the initial thrombus at the wound site. It is a chemoattractant for macrophages which helps to initiate the inflammatory phase

Question 10

What role does TGF-beta play in wound healing?

Answer 10

Transforming Growth Factor-Beta is secreted by macrophages, is a chemoattractant for fibroblasts and stimulates formation of the ECM by fibroblasts. This helps initiate the proliferative phase.

Question 11

How does the collagen pattern change during wound healing?

Answer 11

Proliferative phase: randomly ordered and laid collagen fibers
Remodeling phase: fibroblasts and macrophages replace unordered collagen and replace with cross-linked and oriented collagen fibers. Ordered fibers provide increased strength

Question 12

What is the strength of a well healed wound to the pre-morbid state?

Answer 12

70-80% pre-morbid state

Question 13

How is the collagen make up (type of collagen) different in the proliferative vs remodeling phases?

Answer 13

Type II collagen is most abundant in the early wound healing. By week 2, type III becomes the principal collagen produced by fibroblasts until the remodeling phase. In the remodeling phase, type II collagen is replaced with type I (normal collagen in the dermis) to restore the normal tissue profile

Question 14

What effect does radiation have on wound healing?

Answer 14

1. Radiation causes endothelial, capillary and arteriole damage which can result in progressive & cumulative loss of blood vessels in the affected area.
2. Perfusion may be affected leading to delayed healing
3. Radiated fibroblasts show decreased proliferation, decreased collagen synthesis which leads to diminished deposition of ECM
4. Lymphatic system can be damaged which leads to prolonged edema and poor clearance of infection, debris, bacteria from healing site

Question 15

What factors commonly impair wound healing? (8 common)

Answer 15

1. Nutritional deficiencies
2. Aging
3. Infection
4. Hypoxia
5. Steroids
6. Smoking
7. Diabetes
8. Radiation

Question 16

Why does edema impair wound healing?

Answer 16

1. increasing the distance between cells and vessels that indirectly impair the diffusion process
2. chronic edema may result in protein deposition in the ECM which can act as a diffusion barrier to growth factors and nutrients
3. growth factors and nutrients are relatively diluted in the edematous fluid

Normal tissue= cells and vessels in close proximity for diffusion of oxygen and nutrients

Question 17

What is the mechanism of wound contraction?

Answer 17

Wounds heal by wound contraction, re-epithelialization and scarring. Myofibroblasts orient along lines of tension and pull collagen fibers together. Scar contracture is an abnormal shortening and thickening of a scar that may cause function or cosmetic deformities

Question 18

How much bacterial is needed to cause wound infection

Answer 18

A wound with bacterial counts greater than 10^5th per gram of tissue is considered infected and unlikely to heal without further treatment

Question 19

What factors are responsible for local wound ischemia? (5 common)

Answer 19

1. Smoking
2. Radiation
3. Edema
4. Diabetes
5. Peripheral occlusive diseases

All affect perfusion and oxygenation of a wound

Question 20

What are the benefits of occlusive dressings?

Answer 20

Maintain a moist environment that promotes rapid re-epithelialization and therefore more effective wound healing than when the wound is allowed to dry out

Question 21

What causes hypertrophic/keloid scars?

Answer 21

Excessive inflammatory response during healing is the most likely cause.

Question 22

What treatment options are available for hypertrophic or keloid scars?

Answer 22

There is no definitive treatment options. In most cases, multi-modal therapy include:

1. intralesional steroid injections
2. surgical resection
3. occlusive dressings

Question 23

What features distinguish between a keloid and hypertrophic scar?

Answer 23

Keloid scars extend beyond the original incision and become progressively larger.
Hypertrophic scars are elevated but do not extend beyond original borders of the wound.

Question 24

What population is most susceptible to keloid scars?

Answer 24

Darker skin

Question 25

What population is most susceptible to hypertrophic scars?

Answer 25

Fairer skin

Question 26

Which layer of wound repair contributes the most to wound strength?

Answer 26

Dermal layer. Sutures with prolonged tensile strength should be used to close this layer.

Question 27

What is the role of immobilization in wound healing?

Answer 27

Tension across the skin edges is eliminated, yielding a more favorable scar. Immobilization can be achieved using steri-strips or tapes

Question 28

What influences the permanent appearance of suture marks?

Answer 28

1. Length of time the skin suture remains in place
2. Tension on the wound edges
3. Region of body
4. Presence of infection
5. Tendency for hypertrophic or keloid scarring

Question 29

How does negative pressure vacuum assisted closure help the wound? (4 main benefits)

Answer 29

1. Macrodeformation
2. Microdeformation
3. Fluid removal
4. Stabilization of wound environment

Question 30

With negative pressure wound vac therapy what is macrodeformation?

Answer 30

draws the wound edges together by forcing the wound to shrink via collapse of pores and centripetal forces exerted on the wound surface (essentially accelerating the wound contraction of healing)

Question 31

With negative pressure wound vac therapy what is microdeformation

Answer 31

On a cellular level, increased blood flow, cellular proliferation while inflammatory proteases are removed, bacteria levels are reduced

Question 32

With negative pressure wound vac therapy what is fluid removal?

Answer 32

Removal of fluid assists in removal of toxins and bacteria in the wound bed.

Additionally, by minimizing edema in the wound bed, it allows for better diffusion of oxygen and nutrients

Question 33

With negative pressure wound vac therapy what is stabilization of the wound environment?

Answer 33

In conjunction with fluid removal, osmotic pressure gradients are stabilized. Warm, moist environment with minimal bacteria stimulates better wound healing