Healing and repair

Question 1

Describe fibrous repair

Answer 1

• replacement of functional tissue by scar tissue
• involves angiogenesis, ECM production, cell migration

1. inflammatory cells: blood clot, acute inflammation
2. granulation tissue replaces clot (ECM, angiogenesis)
3. maturation: collagen increases, fibrous scar forms

Question 2

Outline angiogenesis in fibrous repair

Answer 2

• essential for supporting repair by supplying materials
• induced by proangiogenic growth factor VEGF
• pre-existing vessels sprout new vessels
• endothelial proliferation
• endothelial maturation and tubular remodelling
• recruitment of periendothelial cells

Question 3

What is the significance of ECM in fibrous repair?

Answer 3

• anchors cells
• separates tissue compartments
• sequesters growth factors
• allows cell communication
• facilitates cell migration

Question 4

Outline cell migration in fibrous repair

Answer 4

• inflammatory cells: macrophages and neutrophils move due to chemotaxis
• endothelial cells for angiogenesis: angiogenic cytokines
• fibroblasts for ECM/collagen synthesis and wound contraction: pro-fibrotic cytokines

Question 5

Explain the process of regeneration

Answer 5

• replacement of damaged tissue by new, functional and differentiated tissue
• propensity to regenerate depends on tissue type, including: labile (rapid proliferation), stable (variable speed of regeneration) and permanent cells (no regeneration).
• factors which control this are: hormones, growth factors, proteins such as PDGF

Question 6

Describe the healing process in a clean incision wound

Answer 6

• healing by primary intention
• minimal clot and granulation tissue
• epidermis regenerates
• dermis undergoes fibrous repair
• scar maturation can take 2 years

Question 7

Describe and discuss the healing of a large skin defect

Answer 7

• healing by secondary intention
• unopposed wound edges
• large clot dries to form a scab
• epidermis regenerates from base up
• produces lots of granulation tissue
• takes longer and produces bigger scar than primary int.

Question 8

What factors influence the efficacy and healing of repair?

Answer 8

• local: size, apposition, blood supply, infection, foreign material or radiation damage
• general: age, drugs, diet, general health, CV status

Question 9

Outline the type of repair seen in: cardiac, bone, liver, nerve (PNS/CNS) and muscle

Answer 9

• cardiac: fibrous
• bone: callus
• liver: regeneration or cirrhosis
• PNS: wallerian degeneration, distal proliferation
• CNS: no regeneration, gliosis (glial proliferation)
• skeletal muscle: limited regeneration (satellite cells)
• vascular smooth: limited regeneration