Chapter 9 Wound Healing

Question 1

What are the 7 main cellular components of wound healing?

Answer 1

1. Platelets
2. Neutrophils
3. Macrophages
4. Endothelial cells
5. Fibroblasts
6. Myofibroblasts
7. Keratinocytes

(+ lymphocytes)

Question 2

What are the three phases of wound healing?

Answer 2

1. Inflammatory
2. Proliferative
3. Maturation

Question 3

What are the three main types of signalling molecule?

Answer 3

1. Growth factors (=proteins that bind to cell surface receptors with primary result being activation of cellular proliferation/differentiation)
2. Cytokines (=small signalling proteins that have growth, differentiation and activation functions. Secreted primarily by leukocytes)
3. Chemokines (=subset of cytokines with mainly chemotactic function. *Chemotactic = movement in response to chemical stimulus)

Question 4

What is early extracellular matrix vs late ECM composed of?

Answer 4

Fibrin initially –> collagen later

Question 5

Phases of wound healing are broken down into inflammatory, proliferative and maturation. How is inflammatory further sub-divided?

Answer 5

• Haemostasis: reflex vasoconstriction can prevent haemorrgahe from arterioles up to 5mm in diameter. Platelets + coagulation cascade activated. Thomboxane from platelet = powerful vasoconstrictor. Neutrophils, macrophages endothelial cells and fibroblasts attracted.
• Early inflammatory: Establishes immune barrier. Serotonin + histamine –> vasodilation & increased permeability –> extravasation of plasma + leukocyte migration. 24-48 hours.
• Late inflammatory: Establishes macrophages –> debridement + cytokines. Clinically characterised by erythema and oedema. 3-5d after injury

Question 6

By which time point have macrophages usually become predominant leukocyte in wound?

Answer 6

2-5d

Question 7

List 4 funtions that neutrophils in a wound

Answer 7

1. Killing bacteria (release reactive oxygen species. Dependent of high PO₂ - inhibited if PO₂ <40 mmHg. )
2. Breakdown ECM (release proteloytic enzymes)
3. Phagocytosis of debris
4. Release of cytokines to prolong inflammatory phase

Question 8

When does the proliferative phase typically occur and how is it characterised?

Answer 8

4-12d

Angiogenesis, fibroplasia, contraction, epithelialisation. Appearance of granulation tissue

Predmoinant cell types: macrophages, fibroblasts, endothelial cells, epithelial cells

Question 9

VEGF has potent angiogenic activity. By which cells in wound is it predominantly secreted?

Answer 9

Keratinocytes on wound edge.

Question 10

Quiscent mesenchymal stem cells differentiate into fibroblasts 3-5d after wounding and begin synthesysing major comonents of definitve ECM - what are definitive componend to ECM.

What proportions of these are present in unwounded dermis, vs in wounded dermis?

Answer 10

(Pro-) collagen I and III

Unwounded dermis = 80% type I collagen, 20% type III.

In healing wound, type III collagen predominates (after maturation final scar contains around 10% type III)

Question 11

Which signalling molecule is responible for transformation of fibroblasts to myofibroblasts?

Answer 11

Transforming Growth Factor ß (TGF-ß)

Myofibroblasts –> increased alpha-smooth muscle actin (day 6 after wounding). Orientate linearly along lines of tension + attach to ECM –> wound contraction.

Question 12

Which molecule type is predominantly responisble to ECM breakdown?

Answer 12

Matrix metalloproteinases

Question 13

How long does it take for strenght of healing skin wound to plateau?

At what % unwounded strenght does healed tissue plateau?

Answer 13

12-18 months

Approx 70-80%

Question 14

What proportion of various collagens is present in GI submucosa?

Answer 14

68% Type I

20% Type III

12% Type V

Question 15

How long does it take for bladder mucosa to re-epithelialise?

How long does it take a bladder wound to reach near original strength?

Answer 15

2-4 days

3 weeks

Question 16

In the GI tract, which cells predominantly produce collagen?

Answer 16

Smooth muscle cells (vs fibroblasts in skin)

Question 17

What is responisble for reduced GI wound strenght around 2d post-op?

Answer 17

Collagenase. (N.B. activity increased during sepsis)

Question 18

List ways that GI wound healing differs from skin

Answer 18

1. Increased intraluminal pressure during peristalisis –> shear forces.
2. Polymicrobial, aerobic and anaerobic GI flora. Cant reduce by cleaning unlike skin
3. Vascular perfusion more sensitive e.g. during shock (hypotension identified as associated with spetic peritonitis and death)

Question 19

How big a drop in pcv can be tolerated (i.e. GI wound healing not affected) if cardiac output maintained?

Answer 19

15% below normal PCV

Question 20

What are the three prinicples re fascial healing on which a consensus has been reached?

Answer 20

1. Faliure often due to early, high mechanical force.
2. Healing optimized by using continuous non-/slowly absorbable monofilament
3. Sutures placed >3mm from edge, outside active zone of inflammation.

Question 21

BMPs part of TGF-ß family. How do BMPs work?

Answer 21

Stimulate undifferentiated mesenchymal stem cells in periosteum, marrow, endosteum and surrounding muscle to become chondroblasts and osteoprogenitor cells.

Question 22

How long does the maturation phase of bone last?

Answer 22

>1 year

Question 23

In experimental study, how ong did it take for granulation tissue to appear in dog vs cat?

And time until complete granualtion tissue bed?

Answer 23

Dog 4.5 days

Cat 6.3 days

Dog 7.5d

Cat 19d

Question 24

What hormones have been implicated in negatively impacting wound healing?

Answer 24

Androgens

Question 25

List 6 local factors and 3 systemic factors that influence wound healing:

Answer 25

1. Wound perfusion
2. Tissue viability
3. Wound fluid accumulation
4. Wound infection
5. Mechanical factors
6. Envenomation
7. Impaired immune function (endocrinopathy, steroids, ?blood transfusion etc)
8. Cancer
9. Age