Muscle injury- Principles of tissue healing and repair + management Flashcards
What are the stages of tissue healing and repair?
- Bleeding
- Inflammation
- Proliferation
- Remodelling
Describe the bleeding phase of tissue healing and repair
- Bleeding considered to be inflammatory mediator
- Typically lasts 6-8 hours, can last up to 24 depending on tissue type + mechanism of injury
- Local tissue damage due to tear in muscle or local trauma
- Causes vasoconstriction to minimise bleeding and blood flow
- Von Willebrand factors bind to collagen receptors, activate platelets via signalling.
- Platelets have receptors for collagen, bind to collagen, activate further platelets, forms an early platelet plug
- Platelets degranulate, stimulate further coagulation factors e.g. thromibn
- Thrombin amplified during secondary haemostasis, converts fibrinogen into fibrin
- Blood cells become trapped in fibrin mesh, causing early clot, prevents further bleeding
Describe the inflammation phase of tissue healing + repair
- Typically occurs hours after injury and can last for days or weeks
- Cell damage causes release of kinin, histamines, and other chemicals such as WBCs
- Blood vessels dilate, increase blood flow to area, causes redness + heat, brings more nutrients to area, heat increases metabolic rate of tissue cells
- Capillaries become ‘leaky’, can cause edema, which can cause pain and swelling, can also cause clotting of proteins in area, forms a fibrin barrier
- Neutrophils, then monocytes (and other WBCs) enter area, remove damaged and dead tissue cells as well as pathogens from area
What are kinins?
Pro-inflammatory protein, vasodilator, stimulates pain receptors
What is edema?
Fluid in tissue spaces
What are the key signs of inflammation?
- Redness
- Heat
- Swelling
- Pain
- Loss of function/ joint movement
Describe the proliferation phase of tissue healing and repair
- Starts as soon as 24 hrs post injury, can last 2-3 weeks, depending on size + site of injury
- Characterised by the deposition of healing material and the ‘clean up’ of damaged tissue
- Split into 4 key events:
-> Fibroplasia
-> Increase in extracellular collagen production
-> Myofibroblasts cause wound contraction to minimise scarring
-> Angiogenesis
Describe fibroplasia
Formation of fibrous tissue
How is there an increase in extracellular collagen production during the proliferation phase>
- Fibroplasts stimulated and stimulate type III collagen (slightly more elastic than type I collagen) that provide strength and integrity to healing tissue
How do myofibroblasts cause wound contraction to minimise scarring during proliferation?
- Fibroblasts turn to myofibroblast phenotype- thick actin protrusions extent to wound edges and extracellular matrix, this contracts, approximating wound edges
What is angiogenesis?
Formation of new blood vessels
Describe the remodelling phase of tissue healing and repair
- Can last for weeks, months or years
- During, collagen structure maturation and arrangement occurs and results in organised + functional scar
- Key events include:
-> Orientation of collagen fibres
-> Collagen deposition
-> Capillaries diminish in number
-> Tensile strength increases
How are collagen fibres orientated in remodelling?
Due to initial tear, fibres rip apart.
Orientation occurs due to physiological stresses and chemical factors, which reorientate fibres hopefully to become more akin to their natural form
What is collagen deposition in remodelling?
- Type 1 replaces type 3 collagen- gives more tensile strength to wound
What happens when the capillaries diminish in number during remodelling?
- Redness should reduce
