Pathology Flashcards
What are the different types of healing? What are examples of these
-Primary: Typically surgery
-Delayed primary: Wound initially left open then closed at day 2-3
- Secondary Intention: Tissue loss, granulation fills cavity, wound contraction with myofibroblasts
What are the 4 phases of wound healing?
1) Haemostasis
2) Inflammatory
3) Proliferative
4) Remodelling
What happens in haemostasis?
Tissue injury induces clotting cascade.
Platelet aggregation = clot formation
Platelet granules release growth factors initiating wound healing
What are the main inflammatory mediators?
Histamine
Serotonin
Bradykinin
Complement proteins
What happens in the inflammatory phase of wound healing?
Complement cascade activated
Polymorphs migrate to wound after a few hours & act up to 4 days
Monocytes migrate to the wound site & transform to macrophages
What happens in the proliferative phase of healing?
Fibroblasts move into the wound & lay down new extra-cellular matrix
Granulation tissue formation
Angiogensis
Epithelialisation
What happens in remodelling?
2weeks or more after injury can last >1year
Myofibroblasts promote wound contraction
Final product is avascular, acellular scar
What are the phases of fracture healing?
1) Reactive phase
2) Soft callus phase
3) Hard callus phase
4) Remodelling phase
What happens in the reactive phase of fracture healing?
0-7days
Platelet migration & haematoma formation
Acute inflammation
Fibroblast migration
Granulation tissue formation between bony ends
What happens in the soft callus phase of fracture healing?
4days- 3/52
Chondroblasts & fibroblasts migrate into granulation tissue
Lay down hyaline cartilage
Osteoblasts begin to lay down weak form of bone = Woven bone
Hyaline cartilage & woven bone form initial fracture callus which loosely unites bone ends
What happens in the hard callus phase of fracture healing?
1-3months
Osteoblasts differentiate from periosteum cells
Lay down woven & trabecular bone = Hard callus
When can callus be seen on xray
6 weeks
What happens in the remodelling phase of fracture healing?
Up to years
Osteoclasts & Osteoblasts slowly remodel bone to close it to its original shape
Trabecular bone replaced with stronger compact bone
Desceibe tendon healing
Fibroblasts produce type 3 collagen
Large amounts of disorganized collagen produced over weeks
Gradually remodelled over 18months to type 1 collagen
Describe nerve healing
Neuropraxia: Pressure on nerve self resolving over minutes-hours
Axonotmesis: Traction on a nerve, axon degenerates but surrounding tissue intact. Nerve regenerates up to 2cm/month
Neurotmesis: Connective tissue is lost. Neural integrity lost. Recovery limited but can improve with surgical repair
Describe cardiac healing
Necrotic muscle invaded by granulation tissue & fibroblasts- replaced by scar
Impairs ventricular function e.g no longer contractile
Describe brain healing
No fibroblasts in the brain
Necrotic area removed by gliosis leading to volume loss
Neuroplasticity allows some regain of function
What factors lead to chronic wounds?
Infection
Ischaemia
Oedema
Under perfusion
Hypoxia
Further tissue damage
Lack of nutrients
What is the purpose of inflammation?
- Deal with cause
- Remove damage
- Initiate healing
What are the 4 mechanisms of inflammation?
- Acute phase response
- Complement cascade
- Kinin: Kallikrein system
- Prostaglandins & eicosanoids
What substances are released by cells in response to inflammation?
Macrophages: TNFa
Mast cell: Histamine
How do endothelial cells take part in the inflammatory process?
Endothelial cells stimulate release of NO & Prostacyclin causing vasodilation
What effect does vasodilation have on neutrophils?
Migrate towards endothelial surface. Roll along the surface and then stick to it
Endothelial cells contract and full apart allowing neutrophils to move between them and out of the vessel into the tissues
How are monocytes attracted to an area of inflammation?
Stimulate by release of cytokines
