Healing and Repair Flashcards
By what 2 ways can healing occur?
By regeneration
- Replacement with functional, differentiated cells
By repair
- Production of a fibrous scar
What dictates whether healing is carried out using regeneration or repair?
Depends on the severity and location of damage
- Some tissues have better regenerative capacity than others
- Eradication of insult important
- Environmental factors also contribute
- Genetic background (defects in healing capacity
What are the characteristics of labile cells?
- Normal state is active cell division
- Usually rapid regeneration e.g. oral keratinocytes
What are the characteristics of stable cells?
Conditional renewal cells
- Not normally dividing at significant rate
- Speed of regeneration variable
- If forced to can undergo rapid proliferation in response to injury e.g. oral fibroblasts, hepatocytes etc
What are the characteristics of permanent cells?
- Unable to divide
- Unable to regenerate (injury to these can be catastrophic) e.g. nerve cells
What are the 5 stages in the action of wound healing?
- Haemostasis
- Inflammation
- Proliferation
- Remodelling
- Maturation
In the process of wound healing what is ‘haemostasis’?
- Contraction of the capillaries to reduce bleeding
- Red blood cells and platelets released from damaged blood vessels flow into the wound, aggregate and produce a plug or clot in the wound
In the process of wound healing what is ‘inflammation’?
- Dilation of the capillaries - increased permeability allows serum and white blood cells to migrate into the wound area
- Here, the white blood cells differentiate into different cells including neutrophils, and macrophages. These are attracted to the damaged cells and bacteria by chemical substances, they become phagocytic and engulf dead tissue and bacteria
- Once all the dead tissue is eliminated the inflammation gradually subsides
In the process of wound healing what is ‘proliferation’?
- The wound if filled with granulation tissue, which consists of newly formed capillaries and connective tissue
- The formation of new capillaries - angiogenesis - ensures that nutrients are supplied for granulation tissue formation and is essential for wound healing
Fibroblasts are the predominant cells in the proliferation phase, they migrate into the wound site from surrounding tissue and start to multiply - In the last part of this phase the wound is made smaller by wound contraction - this is brought about by specialised fibroblasts with contractile peptides called myofibroblasts
In the process of wound healing what is ‘remodelling’?
- When the granulation tissue filling the wound is almost at level with the surrounding skin, re-epithelialisation starts
- The epithelial cells change shape to facilitate locomotion and crawl across the wound bed to cover it. Migration stops as soon as cells regain contact
The cells change back to their normal appearance and reattach themselves to the basement membrane - the wound is closed
In the process of wound healing what is ‘maturation’?
- The transition from granulation tissue to scar tissue involves reorganisation and maturation of collagen fibres to maximise tensile strength
- During re-modelling the fibred are orientated along the lines of tension and cross linked to form a strong wound
- Remodelling can take up to 2 years after wounding
What are primary intentions in relation to wounds?
Neat cutis like a surgical incision - minimal evidence of scarring
What are secondary intentions in relation to wounds?
More severe than primary - dirty/ragged
What is the proliferation phase of granulation tissue?
- Organisation of tissues is their replacement by granulation tissue
- Laying down of granulation tissue (pink tissue underneath scab) - fundamentally important in the healing process
What is the first stage of the proliferation phase?
- Vascular granulation tissue
- Mix of proliferating capillaries fibroblasts and immune cells
- New capillaries are relatively ‘leaky’ allowing cells and fluid into tissue
