Regeneration and Repair Flashcards
what processes are involved in wound healing
injury
haemostasis
inflammation
regeneration
regeneration
regrowth of cells to the point where theres minimal evidence of injury
can be physiological- making new RBC
when is regeneration possible
minor injuries
-superficial skin incision/abrasion
Where do new cells come from
stem cells
totipotent
produce all cell types
-embryonic stem cells
multipotent
produce several cell types
haematopoeitic stem cells
unipotent
produce one cell type
where are stem cells
epidermis- basal layer
intestinal mucosa-bottoms of crypts
liver - between hepatocytes
labile tissue
Continuous replication of cells
Eg epithelium, haematopoietic tissue
continuously going through cell cycle
stable tissue
Normally low level of replication
But can undergo rapid replication if
required
Eg Liver, kidneys, pancreas, bone, ✓ endothelium, smooth muscle…
left cell cycle but can re-enter
permanent tissue
Cells do not replicate
Eg neurons, skeletal muscle,
cardiac muscle
cannot re enter cell cycle
fibrous repair
the replacement of functioning tissue with a scar
how does a scar form
bleeding and haemostasis
inflammation
proliferation
remodelling
bleeding and haemostasis
Prevention of blood loss
Seconds – minutes
inflammation
Acute then chronic
Digestion of blood clot
Minutes – days
proliferation
Proliferation of: Capillaries (angiogenesis) Fibroblasts Myofibroblasts Extracellular Matrix
Granulation Tissue
(days – weeks)
granulation tissue
functions
- fills the gap
- capillaries supply oxygen and nutrients
- contracts and closes the defect
remodelling
Maturation of scar:
Reduced cell population
Increased collagen
Myofibroblasts contract
Fibrous Scar
(weeks – years)
fibroblast
spindle shaped nucleus
cytoplasmic extensions
secrete collagen and elastin form extracellular matrix
myofibroblast
Between a fibroblast and smooth muscle
Very similar appearance to fibroblast
Express intracellular actin
Can contract
Wound contraction
how are regeneration and repair controlled
Contact Inhibition. Isolated cells replicate until they
encounter other cells. Cadherins bind between cells. Inhibit further proliferation
Polypeptides that act on cell
surface. Causes cell to enter cell cycle
and proliferate. Helpful for healing
Primary intention- healing skin
Incised wound Apposed edges (sutured) Minimal clot and granulation tissue Epidermis regenerates Dermis undergoes fibrous repair
secondary intention- healing skin
Significant tissue loss Unapposed edges (Infection/ulcer/abscess) Abundant clot, inflammation and granulation tissue Considerable wound contraction required (Myofibroblasts) Dermis requires significant repair Epidermis regenerates from edges
fracture healing
1) haematoma surrounds the injury- granulation tissue
2) soft callus- fibrous tissue and cartilage- woven bone
3) Hard callus- woven bone gradually organized into lamellar bone
4) remodelling- lamellar bone remodelled to original bone
complications of fibrous repair- insufficient fibrosis
wound dehiscence
complications excessive fibrosis
keloid scar
complicatons adhesions
fibrous bands that can cause obstructions of tubes
complications loss of function
replacement of specialised tissue by fibrous tissue
complications excessive scar contraction
fixed flexion deformaties- contractures
stages of fibrous repair
Phagocytosis of necrotic tissue debris
● Proliferation of endothelial cells: angiogenesis (the physiological process through which new blood
vessels form from existing ones)
● Proliferation of fibroblasts (collagen) and myofibroblasts (wound contraction)
● Now called granulation tissue
● Granulation tissue becomes less vascular
● Fibrous scar formed
● Contraction of fibrils within myofibroblasts
● Scar matures and shrinks
