Repair And Regeneration Flashcards
What is resolution?
Initiating factor removed e.g. bacteria (antibiotics)
Tissue undamaged or able to regenerate (minimal fibrosis)
How do skin wounds (abrasions) heal?
The most superficial skin wounds e.g road rash
1. Normal skin
2. Abrasion
3. Scab formed over surface
4. Epidermis growing out from adnexa, produced by scab
5. Thin confluent epidermis
6. Final epidermal regrowth
What is healing by 1st intention?
An incision causes very little damage to the tissues on either side of the cut, so if the two sides are brought together accurately the healing can proceed quite quickly
- Can suture up the cut
What is the healing process by 1st intention?
- Incision
- Exudation of fibrinogen
- Weak fibrin join
- Epidermal regrowth and collagen sythesis
- Strong collagen join
Haemostasis – platelets and cytokines forms a haematoma and causes vasoconstriction, limiting blood loss at the affected area
Inflammation – a cellular inflammatory response acts to remove any cell debris and pathogens present
Proliferation – cytokines released by inflammatory cells drive the proliferation of the fibroblasts and the formation of granulation tissue
- the production of collagen by fibroblasts allows for closure of the wound after around a week
Remodelling – collagen fibres are deposited within the wound to provide strength in the region, with the fibroblasts subsequently undergoing apoptosis
What is healing by 2nd intention?
A tissue loss injury or another reason that the wound margins are not apposed requires another mechanism for repair
Can’t being the skin edges together the cut is too deep
What is the healing process by 2nd intention?
- Loss of tissue
- Granulation tissue
- Organisation
- Early fibrous scar
- Scar contraction
- Phagocytosis to remove any debris
- Granulation tissue to fill in defects and repair specialised tissue lost
- Epithelial regeneration to cover the surface
Haemostasis – a large fibrin mesh forms, which fills the wound
Inflammation – an inflammatory response acts to remove any cell debris and pathogens present
There is a larger amount of cell debris present, and the inflammatory reaction tends to be more intense than in primary intention
Proliferation – granulation tissue forms at the bottom of the wound
This is an important step, as the epithelia can only proliferate and regenerate once granulation tissue fills the wound to the level of the original epithelium; once the granulation tissue reaches this level, the epithelia can completely cover the wound
Remodelling – the inflammatory response begins to resolve, and wound contraction can occur
Myofibroblasts are vital cells in secondary intention. They are modified smooth muscle cells that contain actin and myosin, and act to contract the wound; decreasing the space between the dermal edges. They also can deposit collagen for scar healing.
Another example of resolution is lobar pneumonia, how does the lung heal in this case?
Affects a lobe of the lung rather than the whole thing (bronchopneumonia)
Alveoli filled with neutrophil polymorphs (acute inflammation) rather than air
Pneumocytes that line the alveoli can regenerate so the lung can be regenerated - the pneumocytes divide and realign the alveoli
What is repair?
Initiating factor still present
Tissue damaged and unable to regenerate
Replacement of damaged tissue by fibrous tissue
Collagen produced by fibroblasts
This causes scarring
Examples of cells which don’t regenerate? (All in g0)
Heart after MI
Brain after cerebral infarction (fibrosis of the brain = gliosis)
Spinal cord after trauma
Cells that do regenerate?
Hepatocytes
Pneumocytes - but once damage alveoli then it’s repair
All blood cells
Gut epithelium
Skin epithelium
Osteocytes - at first you get callous’ but once human puts force on bone - help remodel bone fractures
What is Organisation?
Organisation is the process whereby specialised tissue are repaired by the formation of mature fibrovascular connective tissue. It occurs by the production of granulation tissue and the removal of dead tissue by phagocytosis
How does granulation tissue repair?
It is loops of capillaries supported by fibroblasts which actively contracts to reduce wound size - this may result in a structure later.
