Wound Repair

Question 1

Tissue repair and wound healing

• what is it?
• what response does it follow?
• what does it involve?

Answer 1

• restoration of tissue architecture and function
• inflammatory response
• both regeneration of uninjured cells and deposition of collagen (connective tissue) to form a scar

Question 2

List all processes/pertinent steps and parts of tissue repair and wound healing (6)

Answer 2

1. Hemostasis
2. Inflammatory response
3. Cell regeneration (if possible)
4. Angiogenesis
5. Formation of granulation tissue
6. Maturation and remodelling of connective tissue scar

Question 3

Cell regeneration

• what is required?
• What is different in each tissue (give 3 types)
• What is regeneration stimulated by?
• What does restoration of normal tissue structure require?

Answer 3

• Proliferation of tissue stem cells or uninjured cells
• Tissues have different cell proliferation capacities:
  1) Labile
  2) Stable
  3) Permanent (neurons, cardiac muscle)
• Regeneration is stimulated by proliferation signals by growth factors
• Restoration requires normal supporting connective tissue framework in residual tissues

Question 4

How are macrophages involved in tissue repair?

Answer 4

• phagocytosis and removal of organisms and dead cells
• activation of other immune cells and inflammatory response
• stimulate proliferation of fibroblasts and deposition of connective tissue (collagen)
• *they do the bulk of the work in running tissue repair

Question 5

Angiogenesis

Answer 5

• process of developing new blood vessels from existing vessels
• -> VEGF (vascular endothelial growth factor) stimulates the proliferation of endothelial cells
• -> new vessels “bud off” the existing ones
• supply nutrients and oxygen needed to support repair process

Question 6

Formation of granulation tissue

Answer 6

• proliferating fibroblasts, loose connective tissue, new and activated blood vessels, and inflammatory cells = granulation tissue (different from granulomas)
• progressively invades and fills in the site of injury
• pink, soft, and granular in appearance

Question 7

Maturation and remodelling

- list steps and aspects (5)

Answer 7

• granulation tissue is replaced over time with dense collagen connective tissue
• collagen provides tensile strength
• as scar matures, blood vessels regress (collagen doesn’t need blood, scars are pale and avascular)
• myofibroblasts contribute to wound contraction
• collagen remodelling by balanced synthesis and degradation of scar tissue

Question 8

Factors that influence wound repair (9)

Answer 8

• infection
• diabetes
• nutrition
• glucocorticoids (steroids)
• poor perfusion
• mechanical factors
• foreign bodies (make it take a lot longer - need to clean these out)
• type and extent of tissue injury
• site of tissue injury

Question 9

Tissue repair in skin

• what does it involve (2 things)
• types (2), based on what?

Answer 9

• involves both epithelial regeneration and formation of connective tissue scar
• 2 types based on nature and size of wound:
  1) first intention
  2) second intention

Question 10

Healing by first intention

• type of injury
• describe healing process (including time!)

Answer 10

• minimal disruption of epithelial basement membrane, death of few cells
• edges of injury close together
  Healing process:
  1) hemostasis immediately, wound fills will blood clot.
  2) Neutrophils enter in first 24 hours and begin to remove dead cells and debris
  3) day 3, neutrophils replaced with macrophages, granulation tissue begins to form. epithelial regeneration continues
  4) day 5, granulation tissue fills the space, and collagen begins to be deposited. epithelial regeneration continues
  5) collagen deposition continues over next few weeks, with remodelling of scar and regression of new blood vessels. Epithelial regeneration concludes.

Question 11

Healing by second intention

• type of injury
• role of scar formation
• differences to first intention

Answer 11

• when cell or tissue loss is more extensive (large wounds, abscesses, ischemic infarctions)
• scar formation plays a greater role than in healing by first intention
• inflammatory reaction is more intense, myofibroblasts needed for wound contraction, more granulation tissue needed

Question 12

Wound contraction

Answer 12

• generally occurs in large surface wounds
• contraction helps close wound by decreasing gap between the edges and shrinking wound deficit
• myofibroblasts contribute to contraction
• can reduce large skin deficits to 10% of their original size in 6 weeks

Question 13

Wound strength

Answer 13

• collagen provides tensile strength but develops over time:
• -> 1 week: wound strength 10% of normal, unwounded skin
• -> increases rapidly over next 4 weeks
• -> wound strength reaches maximum of 70-80% of normal by 3 months

Question 14

Abnormalities in tissue repair

Answer 14

• deficient granulation tissue or scar formation
• hypertrophic scars and keloids
• exuberant granulation
• contractures