Tissue Repair

Tissue Repair

• It is the process of healing after tissue injury.
• It begins as soon as the injury begins.
• It starts with the inflammation.

The steps are

• Stage of Hemostasis
• Stage of Inflammation
• Stage of Regeneration
• Stage of granulation tissue formation
• Stage of remodeling

Types of wound healing 
Healing by primary intention

• Small wound
• Clean wound
• Minimal contamination
• The original tissue regenerates and heals
• Minimal to no scarring
• Functionally excellent
• Occurs in tissue with labile and stable cells.

Healing by secondary intention 

• Large, gaping wound with tissue loss
• Infected wounds
• Wounds with the foreign bodies inside
• Heals with fibrosis
• Function is impaired because of scar contracture.
• Occurs in tissues with the permanent cells.

Stages of repair 
Stage of Hemostasis 

• Vasoconstriction
• Platelet aggregation
• Clot formation

Stage of inflammation

• Signs of inflammation
• Neutrophils recruit in the first 24 hrs
• Then they are replaced by macrophages after 3 days to week

Stage of fibrosis 

• The damaged tissue is replaced by granulation tissue
• It is mediated by different factors
• Cytokines by macrophages like IL1 and TNF 
• Growth factors like TGF, VEGF, PDGF, EGF
• Granulation tissue has active fibroblasts and they are producing different ground substances
• There is angiogenesis
• Healthy granulation tissue looks pink in color with the serous discharge.
• The formed collagen is collagen type III in this phase.

Stage of remodeling 

• The scar becomes smaller due to contraction
• It is mediated by myofibroblasts 
• Excess tissue debris is collected by the phagocytes
• There is regeneration of the normal tissue if possible.
• It takes months to years.
• Contracture of the scar causes functional anomalies.

Repair in specific organs 

Liver

• regeneration of hepatocytes

Brain 

• Gliosis 
• Hydrocephalous ex vacuo

Heart

• Fibrosis

Nerves 

• Wallerian degeneration 
• Nerve regeneration along the nerve sheath if the sheath is intact.

Factors effecting wound healing 

Local factors

• Infection
• Foreign body in the wound 
• Wound shape and size
• Site in the body

General factor 

• Built
• Nutrition
• Co-morbid conditions
• Rest and exercise 
• Habits like smoking and alcohol
• Age 

Hypertrophic scar

• Large scar 
• Injury site 
• Up to 6 months 
• Excess fibroblast 
• Stops after sometime, no Rx
• Type III then type I

Keloid 

• Scar that is very large and growing 
• May extend away from injury site
• More than six months
• Due to genetic predisposition
• Rx needed, steroid or radiotherapy
• Type III excess