Tissue renewal and repair

Question 1

Define regeneration, resolution/maturation, healing and repair

Answer 1

Regeneration - process of complete restoration of damaged tissues to their original structure and function (e.g. liver regeneration).

Resolution/Maturation -removal of inflammatory debris, restoration of normal function, and remodelling of tissues without scarring

Healing - body’s response to injury that includes both regeneration and scar tissue formation.

Repair - the replacement of damaged tissue with scar tissue when regeneration is incomplete, leading to structural but not functional restoration.

Question 2

Classify different types of cells according to their ability to renew

Answer 2

Labile cells;
- continuous division through life
- e.g epithelial cells (skin, gut lining), hematopoietic cells

Stable cells;
- Quiescent under normal conditions; can divide when stimulated
- e.g hepatocytes

Permanent cells;
- Non-dividing, incapable of regeneration
- e.g neurones, cardiac myocytes

Question 3

What are the mechanisms that achieve healing and repair ?

Answer 3

Inflammatory phase;
- initial response to injury, neutrophils and macrophages clear debris
- key mediators are cytokines and growth factors

Proliferative phase;
- fibroblasts synthesise collagen
- angiogenesis = formation of new blood vessels

Remodelling (maturation) phase;
- collagen is reorganised for tensile strength
- capillary density decreases as tissue is remodelled

Question 4

Describe the Role of Granulation Tissue in Repair:

Answer 4

Granulation tissue forms during the proliferative phase.

Key Features:
Fibroblasts - synthesise collagen and ECM components.
Angiogenesis supplies nutrients and oxygen for tissue repair
Macrophages secrete growth factors (e.g., TGF-β) and coordinate repair

Granulation tissue is essential for wound contraction and the transition to scar tissue.

Question 5

Describe cutaneous healing by primary and secondary intent

Answer 5

Primary intention;
- wound edges are approximated
- minimal scarring and faster healing

Secondary intention;
- wound is left open to heal naturally
- larger scar formation due to significant granulation tissue

Question 6

Describe healing in several specialised tissues

Answer 6

Bone - fracture healing involves haematoma formation, callus development, and remodelling

Liver - regeneration via hepatocyte proliferation and stem cells

Nervous system - limited repair in the CNS due to lack of axonal regrowth and glial scarring

Heart - damage is replaced by fibrous scar tissue; no functional regeneration

Skin - involves re-epithelialization and ECM deposition

Question 7

List major local and systemic factors that may inhibit healing

Answer 7

Local factors - Infection, ischemia, foreign bodies, poor wound perfusion

Systemic factors;
- malnutrition (e.g., vitamin C, protein deficiency)
- chronic diseases (e.g., diabetes)
- medications (e.g., steroids, chemotherapy)
- age and immune suppression

Question 8

Describe current advances in regenerative therapeutics

Answer 8

Stem Cell Therapy:
Use of pluripotent stem cells (e.g., iPSCs) to regenerate damaged tissues.

Tissue Engineering:
Bioengineered scaffolds combined with cells to repair tissues.

Gene Therapy:
Introduction of genes to enhance healing or promote regeneration.

Biologics:
Growth factors and cytokines (e.g., platelet-rich plasma) to stimulate repair.

3D Bioprinting:
Printing tissue structures for transplantation or in vitro modeling.