G1/S and G2/M checkpoint checks DNA before and after replication respectively.
Inflammation results in angiogenesis
Vascular endothelial cell growth factor(VEGF) and NO results in increased vascular permeability.
Separation of pericytes from Basement membrane.
Basement membrane breaks down and facilitates the formation of vessel sprout ( results from endothelium proliferation).
FGFs cause migration, proliferation, and maturation of endothelial cell towards the site of injury.
Remodeling of the endothelial cell to form capillary sprouts/tubes( guided by pericytes towards injury).
Elongation of vascular stumps.
Recruitment of pericytes and smooth muscle cells to form the peri-endothelial cells results in maturation of vessel.
Finally, blood vessels sprouts will fuse with other sprouts to build new circulatory systems.
For 2-3 days, the proliferation of fibroblast and endothelial cells results in the formation of granulation tissue(the hallmark of tissue repair)
Microscopy of granulation tissue shows leaky new small blood vessels(product of angiogenesis) that permits leakage of plasma proteins in extracellular space resulting in edema.
Increased accumulation of collagen
Granulation tissue converted to pale avascular scar composed of spindle-shaped fibroblast, dense collagen, fragments of elastic tissue, etc
By the end of one month, scar formation completes and inflammation ceases.
Q) List steps involved in the healing of a wound by the Primary union or First Intention
A)Steps involved in the healing of a wound by the Primary union or First Intention are
Healing by 1st intention means healing of a clean and uninfected surgical incision in the skin joined by surgical sutures which involve the minimal death of the epithelial cell and connective tissue and minimal disruption of the basement membrane.
Formation of a blood clot with trapped RBCs, fibrin, fibronectin and complement components in between sutured margins in the first 24 hrs.
Clot stops bleeding.
Dehydration of the external surface of clot leads to the formation of scab over the wounds.
Neutrophil infiltrates at margins.
Neutrophils release proteolytic enzymes which clean out debris.
Basal cells of epidermis at both cut ends turn mitotic.
Epithelial cells from both edges of wound proliferate.
These cells migrate across the wound.
After 2 days neutrophils are replaced by macrophages.
Epithelial cells fuse in midline and continuity is re-established.
Within 3-7 days granulation tissue begins to invade incision space.
Granulation tissue grows to fill the wound by 5-7 days.
Surface epidermis becomes evenly thickened.
Acute inflammatory response subsides.
Leukocyte infiltrates, edema and angiogenesis disappear during the 2nd week.
Increased accumulation of collagen.
Granulation tissue converted to pale avascular scar.
Wound gradually achieves 80% of its tensile strength of normal skin with few months.
Q) List steps involved in the healing of a wound by the secondary union or second Intention
A) Steps involved in the healing of a wound by the secondary union or second Intention are
Healing of wound by secondary union means healing of a cutaneous wound with a large defect (such as in a laceration and contusion), irregular margins and extensive loss of cells and tissue with more exudate and necrotic tissue.
Large clot/scab is formed
Bleeding is stopped
Severed inflammatory rxn
Abundant granulation tissue at the site of the wound
Extensive deposition of collagen
Myofibroblasts mediate wound contraction(characteristic of healing by secondary intention). This decreases the gap between dermal edges of the wound and reduces the wound surface area.
Type I collagen is responsible for the development of strength
10% after the 1st week
First increases quickly and then slow down during the next 4 weeks
70-80% at the end of 3rd month
Q) How does healing of a wound by the secondary union and primary union differ?
Clean surgical wound
Scanty granulation tissue
Abundant; fills the gap
Complications are rare
Infection and suppuration
Healing results in neat linear scar
Healing results in irregular contracted scar
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