Regeneration And Repair (Session 4) Flashcards
What 3 processes are involved in wound healing?
- Haemostasis (formation of a blood clot)
- Inflammation
- Regeneration and/or repair
What is regeneration?
Regrowth of cells (with minimal evidence of injury)
What injuries is regeneration only possible?
- Minor injuries (superficial skin incision/abrasion)
- If the injury is more extensive than that, tissue has to heal by REPAIR
Is regeneration only done in response to injury?
Explain
- No
- It can also be physiological, e.g. production of new blood cells in bone marrow and new skin cells
Where do new cells come from?
Stem cells
What are stem cells? (4)
- undifferentiated cells
- can differentiate into other fully mature cell types
- can self-renew
- replace dead/damaged cells
What are the 3 main types of stem cell?
What do they do?
Give examples of each
- Totipotent
- produce all cell types
- eg. embryonic stem cells
(T for total) - Multipotent
- produce several cell types, but not all
- eg. haematopoietic stem cells
- Unipotent
- produce 1 cell type
- eg. epithelial stem cells
Give 3 examples of where in the tissues stem cells are found
- Stem cells in the epidermis - found in basal layer (unipotent)
- Stem cells in intestinal mucosa - bottom of crypts
- Stem cells in the liver - between hepatocytes
Tissue regeration types
Labile
Stable
Permanent
Labile tissue:
What it does in terms of regeneration + examples
- continuous replication of cells
- eg. epithelium, haematopoietic tissue
Stable tissue
What it does in terms of regeneration + examples
- normally low level of replication but can undergo rapid replication if required, if that tissue becomes injured or damaged
- eg. liver, kidneys, pancreas, bone, endothelium, smooth muscle
Permanent tissue
What it does in terms of regeneration + examples
Cells do not replicate - left cell cycle and cannot re enter - if damage occurs, they can only heal by repair
Neurones, skeletal muscle, cardiac muscle
Which stage of the cell cycle is each tissue type involved in?
labile - continuous cycling (G1,S,G2,M, back to G1)always in cell cycle
stable - left cell cycle, can re-enter if stimulated (G0)
permanent - left cycle, cannot re-enter
What is required for tissues to regennerate?
An Intact connective tissue/collagen architecture (to build upon)
What happens if there is significant damage to the connective tissue architecture of cells that usually regenerate?
- Regeneration cannot occur
- Instead, healing has to take place in a process called repair
What is fibrous repair?
Replacement of functioning tissue with a scar
In what cases does fibrous repair occur? (scar formation)
Necrosis of permanent tissues : Fibrous repair is the only option
Necrosis of labile or stable tissues:
- Collagen framework has been destroyed
- On going chronic inflammation
Then fibrous repair will occur
What does necrosis of permanent tissue lead to after an injury?
Fibrous repair (i.e. a scar)
What does necrosis of labile or stable tissue lead to after an injury?
- collagen framework intact = regeneration
- collagen framework destroyed = fibrous repair (ie. a scar)
- on-going chronic inflammation = fibrous repair (ie. a scar)
4 stages of fibrous repair (scar formation)
1) Bleeding and haemostasis
2) Inflammation
3) Proliferation
4) Remodelling
BIPR
Bleeding and haemostasis stage of scar formation (3)
- Formation of blood clot
- Prevention of blood loss
- Takes Seconds to minutes
Inflammation stage stage of scar formation (3)
- Acute then chronic
- Digestion of blood clot and necrotic tissue by macrophages and neutrophils
- Takes minutes to days
Proliferation stage stage of scar formation (4)
- proliferation of capillaries (angiogenesis)
- proliferation of fibroblasts and myofibroblasts which lay down extracellular matrix (containing collagen and elastin for tissue architecture)
- The proliferation of all of these results in tho production of granulation tissue
- takes days to weeks
What are the functions of granulation tissue? (3)
- Fills gap - to try and prevent pathogen entry
- Capillaries can supply oxygen and nutrients to the injured area (angiogenesis)
- Contracts and closes wound
What is this an image of?
Label 3 structures that are present
Granullation tissue under microscope with H and E Staining
1) Blood vessels:
- The empty spaces with RBC’s in them
- Lined by endothelial cells
- Abnormal shape (no tubular structure), instead branch in unusual ways (elliptical shape) as they are newly developing, formed because of angiogenesis
2) Chronic inflammatory cells (macrophages, lymphocytes, neutrophils, eosinophils, left over from inflammatory phase of scar formation)
3) Extracellular matrix - pink material (collagen and elastin being laid down as part of scar formation
T/F The vascularity of granulation tissue increases over time
F - The vascularity of granulation tissue decreases over time
How can granulation tissue appear?
Pale yellow and shiny
Remodelling phase (6)
Maturation of scar:
- Reduced cell population (ie apoptosis of inflammatory cells)
- Increased collagen deposition
- Myofibroblasts contract, bringing edges of wound closer together
- Fibrous scar forms
- Takes weeks to years
Which cells involved in fibrous repair, and what do they do? (6)
Neutrophils & macrophages:
- Phagocytosis
- Release inflammatory mediators that control and coordinate the inflammatory response
Lymphocytes:
- eliminate pathogens
- Co ordinate other cells involved in inflammatory processes
Endothelial cell:
- proliferation
- Angiogenesis
Fibroblast - secrete collagen and elastin which forms ECM
Myofibroblast :
- Express intracellular actin
- Wound contraction to make scar smaller and smaller
Name the following cells
How do fibroblasts and myofibroblasts appear on H&E? (4)
Spindle shaped (elongated) nucleus
Star shape cytoplasmic extentions (cant usually see)
- They are similar in appearance
- A myofibroblast is between a fibroblast and a smooth muscle cell
Where is collagen type 1 found? (7)
- Bone
- Skin
- Tendon
- Ligaments
- Sclera
- Cornea
- Vessels etc.
Where is type 4 collagen found? (3)
- Basement membrane
- Lens
- Glomerular filtration etc.
What are thee different names of collagen at different stage
Pre-pro collagen
Procollagen
Tropocollagen
Step 1 collagen synthesis (3)
- Occurs In Endoplasmic Reticulum of (myo)fibroblasts
- Polypeptide alpha chain (pre pro collagen)
- Gets hydroxylated (Vit C dependent)
Step 2 collagen synthesis (3)
- In cytoplasm of (myo)fibroblasts
- Hydroxylated alpha chains are cross linked to form a triple helix
- That triple helix is called procollagen
Stage 3 of collagen synthesis (4)
Occurs in extracellular space:
- Pro collagen gets transported out of cell
- C and N terminals of procollagen cleaved off
- That triple helix left behind is called tropocollagen
Stage 4 collagen synthesis (3)
- Multiple molecules of tropocollagen are cross linked to form a microfibril
- Multiple Microfibrils are cross linked to form a fibril
- Multiple fibrils are BOUND TOGETHER to form collagen fibres
Describe the 4 stages of collagen synthesis
Stage 1:
- Occurs In Endoplasmic Reticulum of myofibroblasts and fibroblasts
- Polypeptide alpha chain (pre pro collagen)
- Gets hydroxylated (Vit C dependent)
Stage 2:
- In cytoplasm of (myo)fibroblasts
- Hydroxylated alpha chains are cross linked to form a triple helix
- That triple helix is called procollagen
Stage 3:
- Pro collagen gets transported out of cell
- C and N terminals of procollagen cleaved off
- That triple helix left behind is called tropocollagen
Stage 4:
- Multiple molecules of tropocollagen are cross linked to form a microfibril
- Multiple Microfibrils are cross linked to form a fibril
- Multiple fibrils are BOUND TOGETHER to form collagen fibres
What class of drugs inhibits collagen synthesis? Why?
corticosteroids are immunosuppressive so inhibit wound healing
Diseases of defective collagen
Aquired:
Scurvy
Inherited:
Ehlers-Danlos
Osteogenesis Imperfecta
Alport syndrome
What is scurvy and why does it result in defective collagen?
- Vitamin C deficiency =
- Inadequate hydroxylation of pre-procollagen
- Defective triple helix structure and defective collagen
Scurvy symptoms/signs (5)
- Poor wound healing
- Tendancy to bleed often from minor injuries
- Bruising
- Bleeding of gums
- Tooth loss
What is Ehlers Danlos syndrome?
What are 4 symptoms?
- inherited disease of defective collagen
- collagen fibres lack adequate tensile strength
- Poor wound healing
- Hypermobile joints
- Easy bone breaking and Joint dislocation
- rupture of the colon and, in some forms, large arteries.
What would the Skin of people with Ehlers Danlos be like? (3)
Hyperextensible
Fragile
Suceptible to injury
What is Osteogenesis imperfecta?
Give 4 symptoms
- Inherited disease of defective collagen
- Brittle bone disease
- BLUE SCLERA - too little collagen so is not transparent
- Easy breaking and dislocation of bones
- Hearing impairment
- Dental abnormalities
What is Alport syndrome?
Give 4 symptoms
- Inherited disease of defective collagen
- X linked - MALE MORE AFFECTED
- Type 4 collagen affected
Symptoms:
Dysfunction of:
- Glomerulus basement membrane
- Cochlea of ear
- Lense of eye
(deafness, eye disorders)
- Blood in urine, which progresses to chronic renal failure
In terms of regeneration and repair, why do cells communicate with each other?
- To stimulate/inhibit proliferation
How is regeneration controlled? (3)
- Direct cell to cell contact
- Local mediators (e.g. growth factors)
- Hormones
How does direct cell to cell contact inhibit repair? (3)
Contact inhibition:
- Isolated cells replicate until they encounter other cells
- Cadherins (cell surface receptors) bind between cells and inhibit further proliferation
In the vein of cell to cell contact, how can cancer arise (4)
- Mutations in cadherins is one of the many causes of cancer
- Cadherins are defective
- They will be unable to tell cells to stop dividing
- Uncontrolled cellular proliferation is one of the hallmarks of cancer
Continued proliferation = multilayers
What are Growth factors?
Polypeptides that act on cell surfaces
What do growth factors do? (2)
- Causes cell to enter cell cycle and proliferate
- Helpful for healing (angiogenesis etc)
Growth factor examples (4)
- Epidermal GF
- Vascular Endothelial GF
- Platelet derived GF
- Tumour necrosis factor
Two types of skin healing
- Healing by Primary intention
- Healing by Secondary intention
Describe healing by primary intention (6)
- Takes place in incision wounds (wounds where the edges of the wound are apposed, next to each other)
- When we sulture a wound, we are bringing edges of the wound together so it can heal by Primary intention
- Minimal clot and granulation tissue = small scar
- Epidermis regenerates (labile tissue type/cell population)
- Dermis undergoes fibrous repair (as it is a permanent tissue type)
- Small scar left, which gets smaller over time
(e.g. my eyebrow scar)
What is healing by secondary intention? (8)
- Significant tissue loss
- Unapposed edges (separated) , so it’s not possible to brig the edges of wound together
- Or there may be something in the middle of the wound, preventing the edges from coming together (ie infection/ulcer/abcess)
- Abundant clot, inflammation and granulation tissue
- Considerable wound contraction required from myofibroblasts in order to try make wound smaller
- Dermis requires significant repair
- Epidermis regenerates from edges
- Takes long time to heal, danger of reinfection and repeated trauma to this wound
Name and describe the stages of fracture healing?
1) Haematoma formation
- Haematoma surrounds injury
- Granulation tissue forms
2) Soft callus formation
- After 1 week
- It is a combo of fibrous tissue and cartilage
- Woven bone begins to form (quite weak)
3) Hard callus formation
- After several weeks
- Woven bone gradually reorganised (by osteoclasts) to lamellar bone (stronger than woven bone)
4) Bone Remodelling
- Takes months to years
- Lamellar bone remodelled to original outline of bone
How long for soft and hard callous formation?
- 1 week soft
- Several weeks hard
How long for a fracture to be completely remodelled?
Months/years
Give 2 types of factors influencing wound healing
- Local
- Systemic
Local factors influencing wound healing (5)
- Size of wound
- Location of wound
- Blood supply to that area of the body
- Infection
- Foreign bodies
Systemic factors influencing wound healing (7)
- Age (older = less efficient wound healing)
- Anaemia/hypoxia/hypovolaemia (= reduced blood supply so less effective wound healing)
- Obesity
- Diabetes (nerve and blood vessel damage)
- Drugs
- Vitamin deficiency (e.g. Vit C)
- Malnutrition
Why would a scar stretch over the years?
elastic fibres don’t regenerate in an area of damaged skin and
therefore scars can stretch as they mature
Complications of fibrous repair (6)
- Insufficient fibrosis
- Excessive fibrosis
- Adhesions
- Loss of function/architecture
- ## Excessive scar contraction
What does insufficient fibrosis result in?
- Wound dehiscence (opening up of a wound)
When does insufficient fibrosis often occur? (4)
- Obese patients
- Elderly
- Malnutrition
- Steroid use
What is known about control mechanisms in regeneration and fibrous repair?
Cells communicate with each other to produce a fibroproliferative response.
Cell to cell communication can occur via what?
- Via local mediators (such as growth factors)
- By hormones
- By direct cell-cell or cell-stroma contact.
Considering local mediators and hormones, cell communication can be: (3)
- Autocrine
- Paracrine
- Endocrine
Describe autocrine signalling
cells respond to the signalling molecules that they themselves produce.
Describe paracrine signalling
a cell produces the signalling molecule, this acts on adjacent cells. The
responding cells are close to the secreting cell and are often of a different type.
Describe endocrine signalling
hormones are synthesised by cells in an endocrine organ, they are then conveyed in the blood stream to target cells to effect physiological activity.
Out of all local mediators, what are some of the most important when it comes to regeneration and fibrous repair?
growth factors
1) What are growth factors?
2) What codes for growth factors?
3) What are growth factors considered as?
4) Why?
1) Polypeptides that act on specific cell surface receptors.
2) Proto-oncogenes
3) ‘local hormones’
4) as they act only over a short distance or even on the secreting cell itself.
1) Describe the variation of what growth factors act on
2) Describe the effects of growth factors
3) Describe how they work
1) some act on many cell types, some have restricted targets.
2) They stimulate cell proliferation or inhibition but may also affect cell locomotion, contractility, differentiation, viability, activation and angiogenesis.
3) They bind to specific receptors and stimulate transcription of genes that regulate the entry of the cell into the cell cycle and the cell’s passage through it.
Name 4 types of growth factor
- Epidermal growth factor
- Vascular endothelial growth factor
- Platelet-derived growth factor
- Tumour necrosis factor
1) What effects does epidermal growth factor have?
2) Name things that produce epidermal growth factor
3) What does epidermal growth factor bind to?
1) Mitogenic for epithelial cells, hepatocytes and fibroblasts
2) keratinocytes, macrophages and inflammatory cells;
3) binds to epidermal growth factor receptor (EGFR)
What does vascular endothelial growth factor do?
potent inducer of blood vessel development (vasculogenesis) and role in growth of new blood vessels (angiogenesis) in tumours, chronic inflammation and wound healing
1) Where is platelet derived growth factor stored?
2) When is it released?
3) Name some other things that produce it
1) stored in platelet alpha granules
2) released on platelet activation
3) also produced by macrophages, endothelial cells, smooth muscle cells and tumour cells; causes migration and proliferation of fibroblasts, smooth muscle cells and monocytes
What does tumour necrosis factor do?
induces fibroblast migration, fibroblast proliferation and collagenase secretion.
1) What happens when normal cells become isolated from other cells around them?
2) What is this called?
3) What process does this occur in?
4) What does this process get altered in
1)
How do cells adhere to each other and extracellular matrix?
What are cadherins?
What are they important in?
What are integrins?
What are they important in?
