2. Wound Healing
Healing is initiated when inflammation begins
Occurs via combination of Regeneration & Repair
3. Regeneration
Replacement of damaged tissue with native tissue
Types of tissue based on regeneration capacity 1-
Labile tissue - they are continuously regenerating i.e.
Bone marrow - hematopoietic stem cells/ CD34+ Skin -
stem cells in basal layer
Lungs – stem cells are type 2 pneumocytes
2-Stable tissue - they don't continuously regenerate but have the ability to regenerate if needed
i.e. regeneration of Liver & Proximal tubule of kidney
3-Permanent tissue - can't regenerate
i.e. Myocardium, Skeletal muscle & Neurons
4. Repair
Replacement of damaged tissue with fibrous scar
Occurs when regenerative stem cells are lost e.g., deep skin cut
Granulation tissue formation-- is the initial phase of repair --consist of 1-
fibroblast (deposit type 3 collagen) 2-
capillaries (provide nutrients)
3-myofibroblasts (contract wound)
Eventually scar formation happens, in which type 3 collagen is replaced with type 1 collagen
Type 3 collagen-- present in uterus, granulation tissue & keloids
Type 1 collagen-- present in bone, skin, tendons & most organs
5. Mechanisms of Tissue Regeneration &
Repair
Mediated by paracrine signaling
via growth factors secreted by macrophages that target fibroblasts
Interaction of growth factors with receptors
(e.g., epidermal growth factor)
results in gene expression and cellular growth
Examples
1-TGF alpha
2-TGF beta
3-Platelet derived growth factor
4-Fibroblast growth factor
5-Vascular endothelial growth factor
6. Normal & Aberrant Wound Healing
Cutaneous healing occurs via primary & secondary intention
Primary Intention
wound edges are brought together
e.g. suturing of surgical incision
Secondary Intention
edges are not approximated
granulation tissue fills the defect, myofibroblasts then contract the wound and forms a scar
Delayed Wound Healing
Due to
1-Infection (most common cause)
2-Vitamin C, Copper or Zinc Deficiency
3-Ischemia, Diabetes & Malnutrition
7. Hypertrophic Scar
Excess production of scar tissue that is localized to the wound
Caused by excess type I collagen
Keloid
Excess production of scar tissue that is way out of proportion to the wound.
Caused by
1-Excess type III collagen
2-More common in African American
3-Classically affects earlobes, face, and upper extremities
Wound Dehecence
Rupture of wound
commonly seen after abdominal surgery
