MoD Session 4 Flashcards
Where do the differentiated cells used in regeneration derive from?
Stem cells
What is regeneration?
Replacement of dad or damaged cells by functional differentiated cells
Describe the proliferation of stem cells.
Potentially limitless
What are multipotent stem cells?
Cells that can produce several types of differentiated cell e.g. Haemopoietic
What are totipotent stem cells?
Cells that can produce any type of cell e.g. Embryonic stem cells
What are uni potent stem cells?
Cells that can only produce one type of differentiated cell e.g. Epithelilal
How do stem cells differentiate?
Asymmetrically - one remains stem cell to maintain pool and one differentiates
In what type of disease can stem cells have therapeutic utility?
Degenerative
Where area totipotent stem cells found?
Blastocyst
Where might unipotent stem cells be found?
Base of crypts of Lieberkühn
What is another term for multipotent stem cells?
Pluripotent
How does the propensity to regenerate vary?
Between cell types
Describe labile cells.
Normal state is active cell division
Usually proliferate rapidly
Constantly progressing through cell cycle
Give two examples of labile cells.
Epithelial
Haematopoietic
Describe stable cells.
Normal state is resting state
Speed of regeneration is variable
Give four examples of stable cells.
Hepatocytes
Osteoblasts
Fibroblasts
Renal tubule
Describe permanent cells.
Unable to divide
Cannot regenerate
Give two examples of permanent cells.
Neurones
Cardiac myocytes
What two mechanisms control regeneration?
Growth factors
Cross talk b/w basement membrane and adjacent cells
How does binding of growth factor to membrane-bound tyrosine kinase receptor cause cellular responses?
Receptor dimerises, forms kinase ability –> acts on membrane bound kinase –> increases transcription factors –> cellular responses
What is the membrane bound kinase acted upon by the dimerised receptor after growth factor binding?
ras
What two pathways can ras take to have effects on a cell exposed to growth factor?
ras –> raf –> mck –> erk –> transcription factors
ras –> P13k –> Akt –> survival, proliferation, migration
Which molecules act as growth factors?
Proteins: EGF, PDGF, FGF
Hormones: oestrogen, testosterone, GH
Autocrine, paracrine and endocrine signals from many cell types
Where does epidermal growth factor come from?
Keratinocytes
Macrophages
Inflammatory cells
What is contact inhibition?
Signalling through adhesion molecules which inhibitis proliferation in intact tissues
What happens to cells that are isolated in culture?
Become motile and proliferate rapidly until a monolayer is formed
What abnormalities of regeneration are seen in cancer?
Abnormalities in growth factors and contact inhibiton
How can contact inhibition be lost in cancer?
E-Catherine binds w/calcium to form a dimer –> allows activation of beta caterin which binds to actin filaments in cytoplasm preventing them from adhering
What is fibrous repair?
Replacement of functional tissue by scar tissue
What must occur for fibrous repair and scarring to be caused?
Necrosis of permanent cells
Necrosis of labile or stable cells with collagen framework damage
If the collagen framework of necrotised labile or stable cells remains intact, what happens?
Resolution of injury and inflammation
What are the key components of fibrous repair?
Cell migration
Angiogenesis
Extracellular production
Extracellular remodelling
What is granulation tissue?
Specialised type of tissue only seen in areas of chronic inflammation and fibrous repair
What cell types are seen in fibrous repair?
Inflammatory cells
Endothelial cells
Fibroblasts/myofibroblasts
What role do inflammatory cells carry out in fibrous repair?
Neutrophils and macrophages phagocytose debris
Lymphocytes and macrophages release chemical mediators
What role do endothelial cells carry out in fibrous repair?
Angiogenesis
What is the function of fibroblasts and myofibroblasts in fibrous repair?
Synthesise extracellular matrix proteins
Wound contraction
What characteristics do myofibroblasts have?
Smooth muscle qualities
Contractile fibres
What are the five steps of angiogenesis?
Endothelial proteolysis of BM
Migration of endothelial cells via chemotaxis
Endothelial proliferation
Endothelial maturation and tubular remodelling
Recruitment of periendothelial cells
What is released from an hypoxic site of injury to induce angiogenesis?
Growth factors e.g. VEGF
Platelets
What role do pre-existing unaffected blood vessels have in angiogenesis?
Sprout new vessels
What exploits angiogenesis so it is not limited by vascular supply?
Malignant cells
What are the functions of the extracellular matrix?
Support and anchor cell Separate tissue compartments Sequester growth factors Allow communication b/w cells Facilitate cell migration through tissues
What is the function of collagen in the extracellular matrix?
Provide extracellular framework
Which types of collagen are fibrillar and where are they found?
I-III
Everywhere
Which types of collagen are amorphous and where are they found?
IV-VI
Basement membrane
What are amorphous collagens quite resistant to?
Enzymes except specific collagenases used for remodelling
How many types of collagen are there?
28
How is fibrillar collagen formed?
Polypeptide alpha chain in ER –> enzymatic modification inc. vitamin C dependent hydroxylation –> alpha chains align and cross link –> soluble procollagen triple helix secreted –> cleaved to tropocollagen –> polymerises to form fibrils which bundle to form fibres –> slow remodelling by specific collagenases
Name three defects of collagen synthesis which cause defective fibrous proteins.
Scurvy
Ehlers-Danlos syndrome
Osteogenesis Imperfecta
Why does scurvy cause haemorrhage and skeletal changes in infants?
Inadequate hydroxylation of alpha chains causes defective helix formation –> collagen supporting BV especially is weak and vulnerable to enzymatic degradation
How does Ehlers Danlos syndrome cause skin laxity, hyper mobile joints and lens dislocation?
Defective conversion of procollagen to tropocollagen
How does the sclera appear in osteogenesis imperfecta?
Thin and blue
What defect of collagen synthesis causes defective amorphous proteins?
Alport syndrome
Why does Alport syndrome cause renal problems?
The basement membrane is disrupted
What maintains tissue integrity and resolution?
Extracellular matrix
What secretes the extracellular matrix?
Fibroblasts
What does the extracellular matrix contain?
Growth factor reservoir
Matrix glycoproteins
Proteoglycans
Elastin
What is the function of fibronectin, laminin and tenascin in the extracellular matrix?
To organise and orientate cells
Support cell migration
What is the function of elastin in the extracellular matrix?
Provide tissue elasticity
What are the three generalised changes sene in fibrous repair?
Tissue becomes more cellular
Increased vascularity
Decreased extracellular matrix
What are the three stages of fibrous repair?
Inflammatory cell infiltrate
Clot replaced by granulation tissue
Maturation
What happens in the inflammatory cell infiltrate stage of fibrous repair?
Extravasation of blood –> clot forms w/ingress of neutrophils around edges causing chronic inflammation –> macrophages and lymphocytes move into clot
What affect does inflammatory cell infiltration have on the area of fibrous repair?
Becomes more cellular
How is a blood clot replaced by granulation tissue in fibrous repair?
Capillaries and lymphocytes sprout and infiltrate
Myofibroblasts and fibroblasts recruit, migrate and differentiate
Synthesis of ECM
Myofibroblasts synthesise glycoproteins
Are granulomas present in granulation tissue?
Nope
What happens during maturation in fibrous repair?
Cell population falls
More collagen is present which matures and remodels
Myofibroblasts contract to reduce volume of defect
Vessels differentiate and decrease in number
Fibrous scar is formed
Comparatively, which stage of fibrous repair is the longest lasting?
Maturation
What controls inflammatory cell recruitment in fibrous repair?
Chemotaxis
What controls angiogenesis in fibrous repair?
Cytokines released by platelets and ECM in response to hypoxia
Give three examples of pro-fibrotic cytokines.
IL-1
TNF-alpha
TGF-beta
What type of cells release pro-fibrotic cytokines causing fibroblast proliferation and ECM synthesis?
Macrophages
What are the two methods of regeneration and repair of the skin?
Primary and secondary intention
When is primary intention used to heal the skin?
Incised wound with opposed edges
How can the clot and granulation tissue seen in primary intention skin healing be described?
Minimal
What causes epidermis regeneration in both primary and secondary intention skin healing?
Loss of contact inhibition
What happens to the dermis in primary intention healing?
Undergoes fibrous repair
When are sutures removed in primary intention skin healing?
~10 days
When skin is ~10% of normal strength
What does vascular granulation tissue lead to after ~2 years in primary intention skin healing?
Scar tissue
Why does primary intention skin healing have good tensile strength?
Minimal contraction and scarring
What forms is infection is trapped in the skin during primary intention healing?
Abscess
What causes a laceration?
Blunt trauma
What causes primary intention skin healing?
Clean, sutured wound
What skin insults will be healed by secondary intention?
Infarct
Ulcer
Abscess
Any large wound where edges are unapposed
What happens to the large blood clot formed during healing by secondary intention?
Dries to form scab or eschar
What is an eschar?
Slough or piece of dead tissue cast off from surface of skin
In which direction does the epidermis regenerate in healing by secondary intention?
From the base up
How much granulation tissue is produced in healing by secondary intention?
Lots
Why is more contraction seen in healing by secondary intention than in primary?
To decrease the larger defect volume
How does the scar formed in healing by secondary intention compare to that formed by primary intention?
Larger, not necessarily weaker
What does skin healing by secondary intention have a higher risk of complications than healing by primary intention?
Takes longer
Why does healing of bone fractures require modification of the repair seen at other sites?
It is a special environment
How does the haematoma form in bone fracture repair?
Ruptured BV in marrow cavity and periosteum
What does haematoma organisation allow in bone fracture healing?
Framework for macrophage, endothelial cell, fibroblast and osteoblast ingress
What happens after the haematoma is organised in bone fracture healing?
Necrotic tissue is removed and capillaries develop to form soft callus
How is woven bone laid down in bone fracture formation?
W/islands of cartilage
What role does the external callus have in the bone during fracture healing when woven bone is being laid down?
Provide splint-like support
What eventually happens to woven bone in fracture healing?
Replaced by lamellar bone and remodelled
What are the stages of bone fracture healing?
Haematoma forms Haematoma organised Soft callus formed Woven bone laid down Woven bone replaced by lamellar bone and remodelled
Give examples of local wound healing factors.
Blood supply Lack of movement Foreign material Size/location/type Infection Apposition Angiogenesis impairment effecting stimulation of (myo)fibroblasts Radiation
What is suppuration?
Infection of a wound causing pus formation
Give examples of general wound healing factors.
General CVS status Age Drugs e.g. steroids or hormones Dietary deficiencies General state of health e.g. chronic diseases
What complications of repair can arise during wound healing?
Insufficient fibrosis
Excessive fibrosis
Excessive contraction
What can loss of wound strength in insufficient fibrosis cause?
Dehiscence
Hernia
Ulceration
What factors increase the risk of insufficient fibrosis?
Obesity
Old age
Malnutrition
Steroids
Why does obesity increase the risk of insufficient fibrosis?
Due to increased intrabdominal pressure
What is the difference between a hypertrophic scar and a keloid?
Hypertrophic = w/in bounds of wound and regresses w/time Keloid = outside wound borders and does not regress w/time
Is surgery useful for treating keloids?
Not really, incision is likely to cause redevelopment
Does the injury have to be severe for a keloid to form?
No, it can be innocuous
Which population is at increased risk of keloid formation?
Afro-Caribbean
How is cirrhosis caused by excessive fibrosis?
Exuberant fibrotic response creates fibrous surrounding to nodules of new cells in liver
What are strictures?
When excessive contraction causes obstruction of tubes and channels
What disease is oesophageal stricture seen in?
Chronic inflammation caused by gastro-oesophageal reflux disease
How is inflammation caused in sigmoid colon leading to formation of a diverticular stricture?
Small herniations of unknown cause in mucosa trap faeces –> inflammation
Fibrous repair creates stricture
In what group of people are diverticular strictures common?
Elderly
If an elderly patient presents with a diverticular stricture, which two main diseases are considered?
Colon cancer
Sigmoid colon
What is a contracture?
Limitation of joint movement due to fibrous scarring over the joint
What wound location causes slow healing?
Over a joint
If part of the liver is removed, how does the organ respond?
Compensatory growth occurs and mass is restored by enlargement of remaining lobes
How do cells in the liver replicate during liver healing?
Almost all hepatocytes replicate during regeneration
Non-parenchymal cells replicate afterwards
Why is there no fibrosis in acute liver damage?
Scaffolding architecture is maintained
Why are nodules formed in chronic liver damage?
Over-exuberant wound healing process causes CT deposition around island of new cells
How does nodule formation in chronic liver disease progress?
Initially can regress but w/increased time becomes permanent
What can nodule formation in chronic liver disease lead to?
Portal hypertension
Cirrhosis
Is chronic liver damage itself symptomatic?
Nope
When do kidney cells heal completely by regeneration?
If collagen framework is maintained
How are epithelial cells destroyed in acute tubular necrosis of the kidney?
Ischaemia
What can cause the hypoperfusion of kidney epithelial cells associated w/hypovolaemia?
Haemorrhage Burns Severe dehydration Pump failure/MI/cardiac tamponade Peripheral vasodilation Sepsis Anaphylaxis Toxins
What toxins can cause hypovolaemia leading to acute tubular necrosis?
NSAIDs
Aminoglycoside antibiotics
Heavy metals
Endogenous filtered proteins
How is the necrosis seen in acute tubular necrosis typically seen?
Epithelial patches still alive and collagen framework intact in some areas
How can the kidney heal so that damage can be undetectable even microscopically?
Remaining epithelial cells replicate using BM as a guide
How does myocyte necrosis progress in the heart?
Endocardium –> epicardium
What percentage of necrotised tissue can be salvaged if the heart is reperfused within 3 hours of MI?
~40%
What can happen to the heart if it is reperfused 6hrs or longer after MI?
Haemorrhage
Reperfusion arrhythmias
What is the regenerative capacity of cardiac myocytes?
Limited if any
What takes place in heart healing?
Fibrous repair for in scar and compromising function
What is the special regenerative tissue used in bone healing?
Callus - woven bone w/islands of cartilage
What is found in the medullary cavity of a healing bone?
Internal callus
What is found at the periosteum of a healing bone?
External callus
How does the callus become trabecular bone in bone healing?
Replaced by lamellar bone which is mineralised
What does cartilage not heal well?
Lack of blood supply, lymphatic drainage and innervation
What is Wallerian degeneration?
Distal portion of severed peripheral nerve swells due to proliferation of Schwann cells
What happens to the proximal axon of a severed peripheral nerve?
Degenerated for 1-2 nodes
If there is good alignment of severed peripheral nerves, what happens?
Axons regrow down previous channels occupied by proliferative Schwann cells
What is unusual in peripheral nerve healing?
Full functional recovery
What happens if there is poor alignment or amputation of peripheral nerve?
Cut ends proliferate disorderly –> tangled mass of axons and stroma called an amputation neuroma which can be painful and require removal
What is the rate of axon growth in peripheral nerve healing?
1-3mm per day
What is the replicative capacity of the CNS?
Evidence suggests it is low
Can the CNS regenerate?
Not effectively
Why can the CNS not regenerate?
It is a permanent tissue
What occurs in CNS healing?
Gliosis
What is gliosis?
Replacement of CNS neural tissues by proliferation of glial cells
Give two examples of disease in which gliosis is seen.
Multiple sclerosis
Stroke
What is the rabbit ear chamber model?
Insertion of plastic chamber allowed in vivo microscopic visualisation of healing and repair due to thin tissue bed development b/w layers of the chamber
