Healing & Repair

Question 1

The body doesnt like empty space so what does it fill it with?

Answer 1

Fibrosis

Question 2

Wound healing is a balance of what?

Answer 2

Regeneration and repair

Question 3

Name the 3 phases of wound healing

Answer 3

Inflammatory phase
Proliferation phase
Maturation phase

Question 4

What are the 3 key players in the proliferation phase?

Answer 4

Cells and cellular factor
Chemical mediators
Extracellular matrix

Question 5

Name the describe the 3 types of cells
Give examples of each

Answer 5

• LABILE - constantly replicating Eg. intestinal mucosa
• STABLE - stable and can replicate - but process is slower and requires a signal to bring the cell back into the cell cycle Eg. liver and kidney
• PERMANENT - very limited or no replicative capacity Eg. brain tissue, cardiac muscle and neurons (heal by repair which usually means fibrosis

Question 6

Where are embryonic stem cells found?

Answer 6

Present in the inner mass of blastocysts

Question 7

Where are adult stem cells found?

Answer 7

Bone marrow - haemopoietic stem cells

Question 8

What cells are important in the INFLAMMATORY phase of wound healing? (1)

Answer 8

• Inflammatory cells for mediators and clean up

Question 9

What cells are important in the PROLIFERATION/REPAIR phase of wound healing? (2)

Answer 9

• Parenchymal cells for return to normal structure and function of the affected tissue
• Endothelial cells for neovascularization/angiogenesis

Question 10

What cells are important in the MATURATION phase of wound healing? (2)

Answer 10

• Fibroblasts for deposition of new ECM (ie collagen)
• Myofibroblasts for wound contraction

Question 11

What does healing require and what is it driven by?

Answer 11

Cell proliferation
Driven by growth factors

Question 12

What is the most important source of GFs?
What do they activate?

Answer 12

Macrophages!
But also epithelial and stromal cells

Activate signaling pathways that drive cells through the cell cycle

Question 13

Name 3 growth factors

Answer 13

• PDGF - platelet derived GF
• TGF-b - transforming Gf
• VEGF - vascular endothelial GF

Question 14

What is PDGF?
What cells produce it?
Its actions?

Answer 14

• A growth factor
• Platelets & macrophages
• Actions
  Chemotactic
  Stimulates fibroblasts and other cells to proliferate
  Stimulates angiogenesis & wound contraction & remodeling by production of ECM proteins

Question 15

What is TGF-b?
What cells produce it?
Its actions?

Answer 15

• A growth factor
• Platelets, T cells & macrophages
• Actions
  Chemotactic
  Stimulated angiogenesis, fibroplasia * production of ECM proteins
  Inhibits matrix metalloproteinase (MMP) production, Keratinocyte proliferation and leukocytes (keeps the response in check)

Question 16

What is VEGF?
What cells produce it?
Its actions?

Answer 16

• A growth factor
• Mesenchymal cells (can become fibroblasts etc)
• Increase vascular permeability, stimulated endothelium to proliferate

Question 17

What is the main pathway triggered by GFs

Briefly explain its steps

What is its importance?

Answer 17

Tyrosine Kinase Pathway

1. GF binds to receptor on cell memb
2. Signal transduction
3. Production of secondary messengers which activate transcription
4. Cellular response (ie replication by cell cycle progression, migration etc)

• Some medication inhibit these pathways eg. treatment of neoplasms

Question 18

Name the layers of tissues
and the components of the ECM

Answer 18

• Epithelial cells
• Adhesion molecules ie integrin
• Extracellular matrix
  >Basement membrane (made up of collagen)
  >Connective tissue
  >*Key cells of ECM- fibroblasts & endothelium

Question 19

Roles of the ECM

Why is it so important?

Answer 19

• Sequesters water and provides turgor to tissues OR sequesters mineral and provides rigidity to bone
• Regulated proliferation, migration and differentiation of cell on and in it –> scaffolding for cell adhesion
• Growth factor reservoir

*Must be intact for tissue to regenerate - integrity of ECM is crucial - need a scaffold to grow on!

Question 20

What is the ECM made up of?

What cells produce the ECM?

Answer 20

Include several types of collagens, elastin, and adhesive type of proteins, including fibronectin, laminin, versican, tenascin, and vitronectin.

Most of the ECM, especially collagen, is produced by fibroblasts

Question 21

Name the key steps of wound healing (8)

Answer 21

1. Trauma (or another cause of tissue damage ie cell death due to hypoxia, neutrophil infiltration etc)

INFLAMMATION PHASE
2. Hemostasis and inflammation –> clotting, removal of dead/damaged tissue and infectious agents –> fibrin and neutrophils in the wound bed

PROLIFERATION PHASE
3. Granulation tissue formation and angiogenesis
4. Cell proliferation and migration (regeneration)

MATURATION PHASE
5. Synthesis of ECM, proteins and collage
6. Tissue remodeling
7. wound contraction (fibroblast - myofibroblasts)
8. Acquisition of wound strength (wks to months)

Question 22

The 3 key components of the PROLIFERATION phase

Answer 22

1. Granulation tissue = proliferation of fibroblasts and blood vessels to fill the defect rapidly
   *fibroblasts, collagen and capillaries - stimulated by GF
   Provides scaffolding for re-epithelialization
2. Angiogenesis = proliferation of small blood vessels
   *required to bring nutrients, oxygen, GFs into the wound bed
3. Re-epithelialisation = proliferation of parenchymal cells
   *requires GFs (eg. keratinocyte GF, epidermal GF etc), ECM and adhesion molecules
   GFs push the cell back into the cell cycle (eg via the tyrosine kinase pathway)
   If basement memb is in tact - its quite quick
   If basement memb is NOT in tact- granulation tissue provides a scaffold

Question 23

Outline the key steps of angiogenesis (7)

Name 4 factors that stimulate it

Answer 23

1. Vasodilation (in response to NO) and increased permeability (induced by VEGF)
   2.** Separation of pericytes** (cells around the outside of blood vessels) from the abluminal surface AND break down of basement membrane (by MMP) to allow formation of a vessel sprout
2. Migration - endothelial cells toward the area of tissue injury - requires GFs, fibrin, ECM and adhesion molecules
3. Proliferation of endothelial cells
4. Remodeling into capillary tubules
5. Recruitment of peri endothelial cells to form mature vessel
6. Suppression of endothelial proliferation and migration and deposition of basement membrane

• HIF-1
• PDGF
• VEGF
• TGF-b

Question 24

The 4 key components of the MATURATION phase

Answer 24

1. Re-synthesis of the ECM - TGF-b produced by macrophages –> stimulate fibroblasts to make collagen (main part of the ECM)
   *Collagen is also the major component of fibrosis - sometimes the defect is large fibrous tissue deposition and repair will dominate
2. Remodeling - tissue injury results in the deposition of various things (eg. inflam exudate, new vessels, granulation tissue, fibrous connective tissue, new parenchymal cells) - this occurs rapidly! –> so is following by remodeling to improve the structural integrity
   This requires deposition and breakdown! - phagocytosis to clean away debris and MMP to break down ECM (produced by macrophages, fibroblasts and other leukocytes)
3. Wound contraction and myofibroblasts - helps to close the wound and bring the edges together
4. Wound strength - Remodeling contributes to the acquisition of wound strength - balance of degradation and deposition of collagen and structural modification of collagen fibres

Question 25

Name 3 factors allowing fibrous connective tissue to form

Answer 25

1. TGF 2. Cytokines like TNF 3. Reduced matrix metalloproteinase (MMP) activity

Question 26

Wound strength (%) after 1wk and 3 months

Answer 26

1wk = 10% 3 months = 70-80%

Question 27

Outline the steps of bone healing (wk 1, wk 3, wk 6) What forms with granulation tissue?

Answer 27

Same process, steps and mediators! Requires greater strength than wound in other tissues Cartilage forms with granulation tissue to form the soft callus! - Wk 1: soft tissue callus = granulation tissue, osteoid and bony remodeling - Wk 3: bony callus = woven bone, granulation tissue, osteoid and cartilage - Wk 6: bony callus = bone resorption (non-stressed areas) lamellar bone

Question 28

Why can brain and PNS not undergo regeneration? What cells are the connective tissue of the CNS? What inflammatory cells are local to the brain?

Answer 28

Neurons are permanent cells so cannot return to the cell cycle No fibroblasts - cant form fibrous tissue (collagen) or granulation tissue **Neuroglia** and **astrocytes** are the connective tissue of the CNS (stable cells) Bcs they cannot proliferate - they form a capsule which results in a central fluid filled cavity = **glial scar** **Microglia** are the brains resident macrophages - clean up the area

Question 29

Healing in parenchymal organs Stroma intact vs not intact

Answer 29

Same steps, cells and mediators as skin but with specific GFs (Eg HGF) Stroma in intact = regeneration Stroma NOT intact = repair (fibrosis)

Question 30

Name 9 causes of delayed healing

Answer 30

1. Infection 2. Diabetes 3. Nutritional status 4. Glucocorticoids (steroids) 5. Mechanical factors (eg increased pressure, over joint) 6. Poor perfusion 7. Foreign bodies 8. Extent of the injury 9. Location (eg. brain vs bone vs skin)

Question 31

Explain the main 2 complication of wound healing

Answer 31

- Too little >**Inadequate connective tissue** --> dehiscence (wound breakdown) (can be caused by steroids (inhibit production of TGF-b which reduced fibrosis in wounds), glucocorticoids, poor nutrition, poor perfusion, mechanical factors or location >**Inadequate vascularization** --> dehiscence (can be caused by damaged immune response, poor nutrition, poor perfusion) - Too much >**Excessive granulation tissue** --> proud flesh (can be caused by mechanical factors like too much movement) >**Excessive fibrous tissue** --> hypertrophic scar, parenchymal fibrosis (can be caused by too much movement or genetic predisposition eg keloids) >**Excessive contraction** --> restricted movement or function (can be due to location of injury eg near a joint)

Question 32

What is matrix metalloproteinase (MMP)? What cells produce it? What is it regulated by?

Answer 32

An enzyme that breaks down the ECM as part of wound healing and remodeling Produced by macrophages, fibroblasts, mast cells and leukocytes Regulated by TIMPs (Tissue inhibitors of metalloproteinases)

Question 33

What is granulation tissue mainly made up of? What does it look like?

Answer 33

Fibroblasts and ECM Red, granular, bleeds easily

Question 34

Describe fibrosis What does it look like?

Answer 34

Granulation tissue and areas of angiogenesis within a wound will mature into regions of fibrosis which have less fibroblasts, more collagen and ECM and less capillaries Firm and white (bcs there is more collagen/matric which gives the wound strength

Question 35

Explain the difference btwn fibrin and fibrosis

Answer 35

Fibrin * protein mesh formed from fibrinogen during the clotting cascade * part of acute inflammation! * forms a temporary clot to stop bleeding * cells: platelets, fibrinogen (**fibrin** via thrombin) Fibrosis * excess **collagen** and ECM deposition * part of chronic inflammation! * part of the healing process but can impair organ function if excessive * cells: fibroblasts, myofibroblasts

Question 36

Explain the difference btwn granulation tissue, a granuloma and granulomatous inflammation

Answer 36

Granulomatous inflammation * type of chronic inflammation - characterized by granuloma formation * predominately composed of macrophages and multinucleated giant cells with some eosinophils and some lymphocytes Granuloma * A nodular lesion with fibrous capsule and often a necrotic center * predominately composed of macrophages within the center of the nodular lesion Granulation tissue * New connective tissue and tiny blood vessels that from during healing - appears in wound repair * Predominately fibroblasts, capillary sprouts (angiogenesis), loose ECM and inflammatory cells * Supports healing by filling the wound and forming a scaffold for tissue regeneration

Question 37

Regeneration VS repair

Answer 37

Regeneration - re-epithelialisation Repair - fibrosis

Question 38

What chemical mediator stimulated fibrosis?

Answer 38

TGF-b

Question 39

What cell types is primarily responsible for the synthesis of collagen?

Answer 39

Fibroblasts

Question 40

Explain 4 ways in which primary and secondary healing differ (using skin as an example)

Answer 40

1. Primary, minimal tissue loss and closely opposed edges Secondary, large areas of tissue loss 2. Primary, minimal inflammation and granulation tissue formation Secondary significant inflammation and granulation tissue formation 3. Primary rapid Secondary slow 4. Primary, minimal scarring or contraction secondary lots of scarring/fibrosis and wound contraction (2)