regeneration and repair Flashcards
what is regeneration
- regrowth fo cells
- minimal evidence of injury
- only possible with minor injuries like superficial skin incision/abrasion
- physiological regeneration e.g production of blood cells in BM
where are stem cells found
epidermis
intestinal mucosa - bottom of crypts
liver - between hepatocytes
how can tissues be classified according to regeneration ability
labile tissue - continuous replication of cells. e.g epithelium, hematopoietic tissue
stabile tissue -low level of replication but can undergo rapid replication id required. e.g liver, kidneys , pancreas, bone , endothelium , smooth muscle
permanent tissue- cells do not replicate. e.g neurons, skeletal muscle, cardiac muscle.
what does necrosis of permanent tissue cause
fibrous repair (scar )
what does necrosis of labile/stabile tissue cause
if the collagen framework is intact then regeneration will occur.
if the collagen framework is destroyed and there is on-going chronic inflammation there will be a scar
how does a scar form
1) Bleeding &haemostasis- prevention of blood loss. occurs in seconds-mins
2) inflammation- acute then chronic. digestion of blood clot. minutes-days
3) proliferation- of capillaries, fibroblasts,myofibroblasts, extracellular matrix. forms granulation tissue (days - weeks)
4) remodelling- maturation of scar: reduced cell proliferation, increased collagen , myofibroblasts contract. fibrous scar forms in weeks- years.
what is the function of granulation tissue
physical barrier to fill the gap preventing microbes, toxins etc from entering.
capillaries supply oxygen and nutrients
contracts and closes the defect
structure and function of fibroblast
spindle shaped nucleus (elongated nucleus) cytoplasmic extensions function - secrete collagen and elastin and form extracellular matrix.
what is a myofibroblast
between a fibroblast and smooth muscle
express intracellular actin
can contract leading to wound contraction
how are regeneration and repair controlled
cells communicate with each other to stimulate/inhibit proliferation
1) direct cell-cell-cell-stroma contact - cadherins bind between cells inhibiting proliferation. also isolated cells can replicate until they encounter other cells.
2) local mediators (e.g growth factors)- GF are polypeptides that act on cell surface causing cell to enter cell cycle and proliferate.
3) hormones
what are the types of healing of skin
primary intention- incised wound. apposed edges. minimal cloth and granulation tissue. epidermis regenerates . dermis undergoes fibrous repair and there will be a small scar.
secondary intention-significant tissue loss. unopposed edges. abundant clot, inflammation and granulation tissue. considerable wound contraction required by myofibroblasts. dermis requires significant repair ad epidermis regenerates from edges
how does a fracture heal
1) haematoma surrounds the injury- granulation tissue
2) soft callus (1 week)- fibrous tissue and cartilage, woven bone (primary bone)
3) hard callus (several weeks )- woven bone gradually organised into lamellar bone.
4) remodelling(months-years)- lamellar bone remodelled to original outline of bone.
local factors affecting wound healing
size location blood supply local infection foreign bodies
systemic factors affecting wound healing
age
Comorbidities- like anaemia, hypoxia,hypovolaemia
obesity - alteration in metabolism due to obesity and increased pressure by surrounding tissue on wound.
diabetes- exces sugar in blood so damage in blood vessels
vit deficiencies
malnutrition
what are the complications of fibrous repair
insufficient fibrosis- wound dehiscence( opening up of previous wounds), occurs in obesity, elderly, malnutrition and steroid use as skin becomes thin
excessive fibrosis- keloid scar
adhesions- fibrous bands that can cause obstruction of tubes.
loss of function- replacement of specialised tissue by fibrous tissue.
disruption of architecture
excessive scar contraction causing constriction of tubes.
