Fibrous Healing and Repair Quiz

Fibrous Healing and Repair

• The process of healing involves two main tissue processes: regeneration and repair.
• Regeneration is the replacement of damaged tissue with identical tissue, while repair involves the formation of scar tissue.
• Different cells have varying abilities to regenerate
• Some cells can regenerate, some can repair, some cannot do either
• Different types of cells are involved in these processes

Intended Learning Outcomes

• Explain the differences between regeneration and repair as a consequence of injury
• Explain the key stages involved in repair and the processes occurring in different tissues like muscle tissues.

Regeneration and Repair

• Two tissue processes are initiated following injury.
• Both processes are responsible for the re-establishment of the structure and function of damaged tissues.

Cell Types Classified by Ability to Regenerate

• The presentation details cell types and their ability to regenerate.

Healing by Primary and Secondary Intention

• Primary Intention:
  • Occurs in wounds where the edges are close together.
  • Usually faster than secondary intention.
  • Results in minimal scarring.
• Secondary Intention:
  • Occurs in wounds with non-opposed edges.
  • Healing happens from the bottom up.
  • Involves significant tissue loss or damage.
  • Formation of fibrovascular connective tissue (fibrous scar tissue).

Repair - 4 Phases

• The healing process typically involves four phases: Hemostasis, Inflammation, Proliferation, and Remodeling.

Repair - 4 Phases: Detailed Description

• Hemostasis: (Few hours)

  • Platelet aggregation
  • Fibrin clot formation
  • Leukocyte migration
  • Removal of foreign particles and bacteria

• Inflammation: (1-6 days)

  • Chemoattractant release
  • Phagocytosis
  • Removal of foreign particles and bacteria

• Proliferation: (4-21 days)

  • Provisional ECM synthesis
  • Fibroblast proliferation
  • Granulation tissue formation
  • Re-epithelialization

• Remodeling/Maturation: (3 weeks to 2 years)

  • Type I collagen accumulation
  • Crosslinking of collagen
  • Scar tissue formation
  • Increase in tensile strength

Inflammatory Phase

• Leukocytes (WBCs) enter the wound (includes neutrophils, lymphocytes, and macrophages)
• Macrophages phagocytose damaged tissue & bacteria
• Release of proteases (enzymes) breaking down necrotic tissue
• Release of cytokines to regulate new tissue formation
• Release of matrix metalloproteinases to assist in clearing damaged extracellular matrix
• Growth factors activate cells involved in the inflammatory process

Proliferation/Rebuilding Phase

• New tissue is regenerated and constructed by fibroblasts responsible for blood vessels, collagen and connective tissues.
• Capillaries join together forming a scaffold.
• This develops into granulation tissue filling the wound cavity.
• Granulation tissue will change colour as new blood vessels develop.

Remodeling Phase

• This phase lasts 21 days to 2 years.
• Epithelial cells from hair follicles, glands and around wound edges move over newly formed granulation tissue, contracting to pull edges together.
• Macrophages reorganize collagen within the newly healed area forming a scar
• Key fact: Macrophages reorganize collagen within the newly healed wound to form a scar.

Muscle Healing and Repair - 3 Stages

• Stage 1: Muscle degeneration and inflammation
  • Muscle damage leads to degeneration and inflammation
  • Satellite cells become activated
  • These cells secrete growth factors like IGF-1 and HGF.
  • This activation and proliferation of satellite cells promotes muscle regeneration
• Stage 2: Muscle regeneration
  • Myoblasts from satellite cells fuse to form myotubes.
  • These myotubes participate in repairing existing muscle fibres
• Stage 3: Muscle fibrosis
  • Presence of TGF-B1 at injury site.
  • Fibroblast deposition and ECM deposition.
  • Scar tissue formation.

Satellite cells in Muscle Healing

• Muscle fiber damage triggers dormant satellite cells to activate.
• They proliferate and create new dormant satellite cells and differentiated myoblasts.
• Myoblasts either form a new fiber or patch the existing one.
• Cells from elsewhere, such as bone marrow, can also be involved.

Repair Phase - Two Phases

• Regeneration of disrupted myofibres
• Formation of connective tissue scar by fibrin and fibronectin.
• Scar tissue strength and anchoring to allow fibroblast invasion.
• Satellite cell proliferation into myoblasts.
• New myoblasts fusing with injured myofibres.

Remodeling

• Detailed description of the stages in remodelling based on the slides provided
• The images illustrate how connective tissue scar forms, and how the muscle tissue is virtually fused together.

Recap

• Questions to consider:
  • What's the difference between repair and regeneration?
  • Explain healing by primary and secondary intention?
  • Describe the four stages of wound healing?
  • Describe the three stages of muscle healing?