Healing And Repair- muscle Flashcards
What happens after injury occurs
Injury ⬇️ Inflammation ⬇️ Repair :
1) tissues capable of regeneration
* Regeneration process- replacing injured or dead cells functional identical cells
> limited injuries- regeneration of normal anatomy
Extensive injury- partial regeneration and scarring (repair by fibrous healing)
2) tissues not capable of regeneration
Repair and organisation process
> scarring only (repair by fibrous healing)
Cell types (classified by ability to regenerate)
Labile cells
stable cells
permanent cells
Labile cells
Epithelial cells in skin and digestive system
The cells undergo continuous proliferation have a short lifespan
Stable cells
Bone cells liver cells
Usually divide in frequently but can divide rapidly when stimulated by lost cells for example a fracture
Permanent cells
Neurons cardiac muscle
Divide only in the fetus and cannot be replaced with lost
Healing by first intention
Eg a cut or a bone fracture
loss of part of a labile or stable cell population can be completely restored
The result is indistinguishable from normal has minimal defect
Healing by second intention
Eg healing of open wound or 3rd° burn
Extensive tissue loss or damage requires a repair process
Involves the formation of fibrovascular connective tissue- fibreous scar tissue
Tissues not capable of regeneration
Tissue repair stages
Three overlapping processes:
Inflammation
Proliferation
Remodelling
End of inflammation/beginning of proliferation
1)Role of macrophages: leaked out of capillaries go to affect area
Neutrophils- degrade pathogens
Monocytes- release enzymes phagocytosis secrete cytokines which attract cells for proliferation
2)Angiogenesis: new capillary blood and blood vessels are formed from pre existing blood vessles
Endothelial stem cells from undamaged part of vessles migrate to the damaged area attracted to area by chemicals- fibronectin found on fibrin scab and other angiogenic factors released by cells such as macrophages and platelets.
Endothelial growth and proliferation are directly stimulated by hypoxia and lactic acid in the wound. New capillaries formed eventually forming a blood Flow through the region which supplies nutrients and get rid of metabolic waste
3)Migration of fibroblasts to the area of damage
At the same time there is an increase of fibroblasts that were on site numbers peak at 1 to 2 weeks after Injury occurred. Main cells. Fibroplasia ends 2/4 weeks after wounding.
Production of cells decrease indicators proliferation is beginning.
Healing and repair – proliferation
1)Roll fibroblasts-Form granulation tissue
•Migrate to the site of wound
2)Fibroblasts secrete the extracellular matrix and collagen e.g proteoglycans (look at inflammation)
- Forms a new mesh work (scaffolding)
- Haphazard arrangement of immature fibres immature type 3 collagen
3) More organised bundles of collagen are formed as more collagen is laid down and the repair is gradually strengthened near the end of proliferation intermolecular cross links are formed between collagen fibres and this strengthens repair but can reduce extensibility of tissue as they cannot slide over each other.
4) new tissue = granulation tissue and it contains new capillaries and cells called myofibroblasts
5) contraction of the repair begins the action of myofibroblasts which are specialised fibroblasts - collagen secreting but also contain muscle like contractile proteins
6) They attached to edges of the wound and each other and contract to pull the wound edges together- smaller wound scar develops
**Fibronectin is important because it acts as an anchor for myofibroblasts
Importance of fibronectin
** Fibronectin is important because it acts as an anchor for myofibroblasts
Duration of proliferation
3 weeks
Remodelling
1) Fibroblasts and myofibroblast start to leave the scare Tissue changes from a predominantly cellular to fibrous structure
2) Change of collagen type from the immature type 3 to mature type 1
3)Gradual realignment of collagen fibrrs along the lines of stress to attain the mechanical characteristics of the tissue prior to injury
more parallel than haphazard. Proteoglycans etc affected by direction and magnitude of stress.
4) fibroblasts are aligned parallel to lines of stress mechanical forces influence metabolism increasing production in extracellular matrix, fibronectin= parallel to lines of stress so if patient doesn’t move these processes won’t occur. Exercise v important movement =6 months
5) Vascularity of scars diminishes
Remodelling duration
6 months
Muscle healing and repair
How muscles are injured
Muscle tissues heal by regeneration and repair
1) Muscles injured by direct trauma - fracture or blow
2) mechanical strain- stretching forces eccentric
3) exercise or ischaemia - compression lack of O2:
- Tearing/rupture of muscle
- Intramuscular blood vessels torn
- Torn muscle fibres retract and the gap between the stumps is filled with haematoma
