healing and repair Flashcards
in which type of inflammation is the tissue completely restored?
acute inflammation
which type of inflammation is associated with greater tissue destruction?
chronic
which type of inflammation can healing arise from?
both acute and chronic
- regeneration of infected tissue (acute)
- repair of tissue (chronic)
what is regeneration?
replacement with functional, differentiated cells
what is repair?
production of a fibrous scar and changes in tissue structure/architecture
what are the factors which influence whether a tissue is regenerated or repaired?
- severity
- location
- regenerative capacity
what are the three cell types on regeneration/repair?
- labile
- stable (conditional renewal)
- permanent
what is the function of labile cells?
- normal state is active cell division
- rapid regeneration
what is an example of labile cells in oral cavity?
keratinised epithelium
what are stable cells?
- variable rates of regeneration
- rapid proliferation in response to injury
what is an example of a stable cell in the oral cavity?
fibroblasts
what are permanent cells?
- unable to divide
- unable to regenerate
what is an example of a permanent cell in the oral cavity?
nerve fibre
what are the four stages in healing?
- coagulation phase
- inflammation phase
- proliferative phase
- maturation phase
describe the coagulation phase
- haemostasis
- clot formation (coagulation system – acute inflammation)
- mitosis of labile/stable cells (e.g., epithelial cells)
describe the inflammation phase
- macrophages/neutrophils phagocytose and degrade infectious agent
- stimulation of certain cells (e.g., keratinocytes/fibroblasts) to start regenerating and/or repairing tissue
describe the proliferative phase
- formation of granulation tissue
- fibroblasts are key players
- new connective tissue (rich in collagen)
- angiogenesis (formation of new blood vessels)
- growth factors are essential
what are the two phases of granulation tissue?
- vascular granulation tissue
- fibrous granulation tissue
describe vascular granulation tissue phase
- tissue is highly vascularised (allows flow of immune cells and plasma proteins)
- mix of proliferating capillaries, fibroblasts, immune cells
- new capillaries are relatively ‘leaky’ allowing cells and fluid into tissue
describe the fibrous granulation tissue phase
- more fibrous tissue
- over time capillaries regress and immune cells return to blood
- mature fibroblasts lay down collagen
what colour do macrophages stain?
purple
what colour do fibroblasts stain?
pink
what is angiogenesis?
formation of new blood vessels
what are the two mechanisms for which angiogenesis can occur?
- sprouting
- intussusceptive (splitting)
driven by growth factors (vascular endothelial growth factor)
VEGF gradient
what are examples of growth factors?
- cytokines
- hormones
what are growth factors?
- promote/inhibit cell growth and differentiation
- bind receptors on cell surfaces
- homeostatic production (balance in health)
- alteration in this balance causes dysregulated cellular proliferation and survival of abnormal cells
what are the functions of growth factors?
- promote cell survival
- locomotion
- contractility
- differentiation
- angiogenesis
what is fibrosis?
- deposition of collagen and formation of excess fibrous connective tissue
- driven by fibroblasts and macrophages
- arises with substantial or repeated damage eg chronic inflammation
- macrophages M1 or M2 control fibroblast function
describe the role of macrophages in fibrosis
- M2 macrophages are essential in healing and repair
- engulf/degrade
- produce growth factors eg TGFB, PDGF, VEGF etc
describe the maturation phase of healing
- disorganised granulation tissue remodelled by remaining cells
- collagen fibres are cross linked along tension lines
- re-epithelisation (growth factors)
- regain of tensile strength (up 80% of pre-injury strength)
- fibrous scar remains (in repair)
- tissue remodelling
what is primary intentions?
regeneration of tissue (acute)
what is secondary intentions?
regeneration and repair (chronic)
what are the phases of healing in a hard tissue eg bone?
- inflammatory phase
- repairing phase
- remodelling phase
describe the inflammatory stage of fracture healing
- hematoma formation (blood clot within the tissue) at fracture
- occurs within 48 hours
- acute inflammatory response – inflammatory infiltrate scavenge debris and dying tissue
- bone cells deprived of oxygen/blood supply die off
describe the repairing stage of fracture healing
- capillaries form into hematoma
- occurs within weeks
- fibroblasts produce collagen fibers
- osteoblasts form spongy bone
- granulation tissue forms (similar to soft tissue healing)
- granulation tissue becomes the fibrocartilage callus (soft callus)
- cells involved in bone remodelling (chondrocytes and osteoblasts) produce cartilage and bone
- remaining granulation tissue is ossified (turned to bone)
- formation of hard bone callus at fracture site (known as Fracture Callus or woven bone)
- cccurs within months
describe the remodelling stage of fracture healing
- osteoclasts and osteoblasts remodel the hard bone callus (resorption vs deposition of bone)
- cortical bone replaces woven bone.
- takes between months and years – may never fully repair
- angiogenesis essential in bone regeneration and repair
