Tissue Injury & Repair 3: Healing by first and second intention

Question 1

What is proud flesh? When does it normally occur?

Answer 1

Essentially it is granulation gone wrong: over proliferation of granulation tissue. -Fibroblasts proliferation: never stop making granulation tissue. - Continuous low level neutrophilic inflammation. -Frequent complication of limb wounds in horses. (not body, not ponies) -Most common NON NEOPLASTIC proliferative cutaneous lesion.

Question 2

What would be a differential diagnosis of proud flesh?

Answer 2

Sarcoid: will have the same gross appearance. Sarcoids are flat, verrucous (wet like) or nodular. They are non productive infection of Bovine papillomavirus. -Locally agressive ( non metastatic) fibroblastic tumors. MOST COMMON NEOPLASTIC SKIN TUMOR OF HORSES AGES 3-6.

Question 3

Where do sarcoids usually occur and when?

Answer 3

Develop in traumatized areas or at sites of wounds 6-8 months after healing. Commonly found on head, legs, ventral trunk and may be multiple found. (Proud flesh only on limbs) Usually a biphasic progression: 1. Epidermal hyperplasia with rete pegs. (rete pegs are epithelial extensions that penetrate the underlying connective tissue) 2. Fibroblastic proliferation

Question 4

What is a distinctive histological feature of Sarcoids not seen in granulation tissue?

Answer 4

Fibroblasts found at the dermal-epidermal junction are orientated perpendicular to the basement membrane whereas in granulation tissue they are parallel and the BV’s are perpendicular. If epidermis becomes ulcerated can be difficult to identify.

Question 5

Cutaneous would healing involves what two healing processes?

Answer 5

1. Regeneration of the epithelium 2. formation of connective tissue scar.

Question 6

What are the 3 main overlapping phases during wound healing?

Answer 6

1. inflammation 2. formation of granulation tissue 3. ECM deposition and scar formation (remodeling) Larger wounds contract during the healing process.

Question 7

What is meant by 1st intention scarring? Give an example from class.

Answer 7

Focal disruption of epithelium and basement membrane. Death of only a small number of epithelia and connective tissue cells. Therefore regeneration and very little scarring should occur. Epithelial regeneration predominates over fibrosis. Ex: Simple surgical incision site. Small incision, clean, uninfected, closed with sutures.

Question 8

Describe the process of First Intention healing 24hrs -7 days post sx.

Answer 8

1. Neutrophils migrate into fibrin blood clot followed by macrophages. 2. Basal cells along the incision margins begin to show mitotic activity. 3. epithelial cells migrate and proliferate across the dermis and deposit BM (along with mesenchymal cells) as they progress. Epidermis becomes thickened due to hyperplasia. 4. Fibroblasts migrate in, proliferate and start to produce collagen and BV start to form granulation tissue.

Question 9

Describe the process of First Intention healing in the early weeks after sx.

Answer 9

Collagen continues to accumulate as fibroblasts decrease in #. Blanching occurs= Vascular regression and increased collagen. Sutures are out @ 10 days and the epithelium should in intact.

Question 10

Describe the process of First Intention healing in months to a year after sx.

Answer 10

Scar is formed from dense connective tissue covered by normal epidermis. Increases in strength. Any dermal appendages that were destroyed (hair follicles) are lost permanently.

Question 11

What is meant by Second Intention Healing?

Answer 11

Tissue loss is more extensive. -Injury could be due to abscesses, ulceration, larger wounds where a more intense inflammation is occurring. -Abundant development of granulation tissue. -Wound contracts by action of myofibroblasts.

Question 12

2nd intention healing: 1-2 weeks.

Answer 12

Phase of rapid proliferation of granulation tissue Slough and scab. Epidermal proliferation Vascular granulation tissue Hyperemia

Question 13

2nd Intention Healing: 3-6 weeks.

Answer 13

Epithelial proliferation across granulation tissue surface before gradually shedding scab. Granulation tissue begins to contract pulling wound edges closer together. Hyperemia in the end will get large fibrous scar, pale, with this epidermis over it, devoid of hair follicles. Compared to first intention where you will get linear fibrous scar.

Question 14

What is wound contraction?

Answer 14

within 6 weeks, large defects should be reduced by 5-10% of its original size. Occurs due to the presence of myofibroblasts which are modified fibroblasts exhibiting features of contractile smooth muscle.

Question 15

Corneal Ulcers: Mild persistant irritation results in…

Answer 15

cutaneous metaplasia (becomes skin) 1. Epithelial hyperplasia 2. Hyperpigmentation 3. Stromal scarring

Question 16

Corneal Ulcers: Rapid and or severe injury results in….

Answer 16

Ulceration

Question 17

What can we expect to see in shallow corneal ulcers?

Answer 17

These are too rapid or severe for metaplasia or necrosis. Usually results in ulceration. Immediate stromal edema due to absorption from tear film. Neutrophils absorbed from tear film Epithelial cells flatten and slide across the ulcerated surface.

Question 18

What can we expect to see in deep corneal ulcers?

Answer 18

Edema -Neutrophilic inflammation -Neutrophil-mediated stromal lysis -Ingrowth of fibroblasts and blood vessels from limbus to form granulation tissue -epithelial regeneration following stromal rebuilding. -Granulation tissue matures to resemble normal stroma. -Corneal clarity permanently impaired.

Question 19

Gross appearance of healing deep corneal ulcers?

Answer 19

Corneal edema will appear white due to edema and inflammatory cells. Red Brush border= ingrowth of blood vessels which repair stroma to allow epithelium regeneration on top of it. (WANT THIS TO HAPPEN) Descemetocoele= Bulging of descemet’s membrane. (BM between stroma and corneal endothelium)

Question 20

Why is wound healing more favorable in ponies than horses?

NOTE: PAST EXAM QUESTION: DESCRIBE TO OWNER* HOW THIS HEALING PROCESS WORKS!

Answer 20

Ponies:

• Inflammatory phase faster and more intense.
• Greater contribution of wound contraction.
• Epithelialization contributes less due to rapid wound contraction whereas in the horse it is the primary method of wound closure.
• Wounds of ponies heal more favourably, lower cost of treatment

Horses:

• Inflammatory phase is weaker and persists - lower initial production of inflammatory mediators.
• Formation of granulation tissue is excessively fast and persists, due to the unrelenting inflammatory response
• More extensive scar formation because epithelialisation is the primary method of wound closure v. ponies where wound contraction is primary method and epithelialization is secondary and contributes less.

Question 21

What part of the body is wound healing difference most significant when comparing horses to ponies?

Answer 21

• Significant with limb wounds moreso than body wounds.
• The main difference between the wound healing is the inflammatory process (horses is weaker and more prolonged), Ponies is rapid and more aggressive.
• Ponies have better wound contraction, therefore they have less epithelialisation and smaller scar formation.
• Horses have excessively fast granuloma formtion due to the persistant inflammatory process, therefore they have more extensive epithelialization and due to this they have large scar formations than ponies.

Question 22

What factors prevent or delay the healing process?

Answer 22

1. Infection- single most important cause due to prolonged inflammatory process.
2. Nutrition- protein deficiency inhibits collagen synthesis.
3. Mechanical Factors- trauma or torsion= wounds may pull apart (dehisce)
4. Anemia, blood supply, oxygen tension
5. Age/ physical status
6. dehydration
7. wound fluids (pockets of blood or serum)
8. Inappropirate dressings
9. Foreign bodies (plant material, glass fragments, bone fragments.
10. Underlying neoplasia.

Question 23

How would the volume of tissue injured play a role in would healing?

Answer 23

In tissues comprised of labile and stable cells (cells that divide and proliferate), extesnisve tissue injury will result in incomplete regeneration and at least partial loss of function.

Tissues comprised of permanent cells (myocardium) will result in scarring.

the brain has no fibrocytes so no scarring occurs in the CNS.

Question 24

How does the location of the injury play a role in wound healing?

Answer 24

Extensive exudate production could cause adhesion to the thoracic cavity if there was pleural inflammation.

Large accumulations of exudate undergo organization which is when granulation tissue grows into it and a scar forms.

Question 25

What are the main characteristics in Wound healing in reptiles when compared to other species?

Answer 25

1. Scar tissue maturation is slow
2. Sutures remain in for 4-6 weeks rather than 10 days.
3. Ecdysis: shedding of scales is cyclical therefore the activity of the epidermis and dermis promotes healing.
4. Mainting reptiles at the upper end of their optimal environmental temperuatre range promotes healing.
5. Wounds orientated cranial to caudal heal more quickly than transverse wounds.