Repair - Tue Lec

how does the body respond to injury?

what are the 3 phases of wound healing?

1. inflammatory

2. proliferative

3. remodeling

what happens during the inflammatory phase of wound healing? who is playing a role?

• changes in blood flow and permeability

• clot formation, growth factor

• players; neutrophils, macrophages and lymphocytes

what happens during the proliferative phase of wound healing? who is playing a role?

• collagen deposition

• fibroblasts!

what happens during the remodeling phase of wound healing? who is playing a role?

• collagen crosslinking

• fibroblasts!

what are the inflammatory responses to wound healing?

1. clot formation

2. immune cells will be recruited; neutrophil, monocytes, lymphocytes

purpose of clot formation

1. stop bleeding

2. scaffold for migrating cells which are attracted to the growth factor, cytokines and chemokines released into the area

what is the fundamental structure of a blood cot?

protein fibrin that traps a mass of aggregated platelets

• platelets will shed from megakaryocytes

what are the 3 steps of clot formation?

1. vascular spasm

2. platelet plug formation

3. coagulation (clotting)

what are the 3 steps of the proliferative phase?

1. Neoangiogenesis / angiogenesis

2. fibroplasia - laying network of collagen (III)

3. epithelialization or proliferation of parenchymal cells

fibroplasia

fibroblast proliferation and synthetic activity (laying collagen III in wound)

epithelialization

epithelial cells from wound margins migrate inward to cover wound

what occurs during the end of the proliferative phase and throughout the remodeling phase?

1. tissue remodeling

2. wound contraction

3. increase wound strength over time

what happens to fibroblasts during wound contraction?

change in phenotype → now called myofibroblasts

• express more actin

• exhibit features of contractile smooth muscle cells

what happens to the wound as it gets stronger?

• leukocyte, edema and increased vascularity are diminished

• collagen remodeling from type III to type I

granulation tissue

new connective tissue (collagen III) that forms in a healing wound

• fill in with new blood vessels and tissue

• myofibroblasts contract wound and modify type III collagen to type I (stronger)

what are the 3 types of wound healing?

1st intention (Primary) Healing

2nd Intention (Secondary) Healing

3rd Intention (Tertiary) Healing = Delayed closure

Primary Intention healing

tissue surfaces have been closed (approximated)

• stitches, staples, or skin glue, or tapes

what is the purpose of primary intention healing?

allow healing prior to the formation of granulation tissue (scars will occur)

healing occurs by wound epithelialization and CT deposition

Secondary intention healing

• large wounds associated with tissue loss

• edges cannot be brought together! - granulation tissue will form

• open wound will close by contraction and epithelialization

Secondary vs. Primary Intention Healing

secondary;

• scar formation is greater

• repair time is longer

• higher risk of infection

tertiary intention healing

aka. delayed closure

occurs when there is a reason to delay suturing

• wounds require more CT (scar tissue)

example of tertiary intention

abdominal wound that is initially left open to allow for drainage but is later closed

identify picture

granulation tissue on the left and scar tissue on the right

left; type III collagen, neovascularization, edema, fibroblasts and macrophages

right: type I collagen, less blood vessels, few fibroblasts and macrophages

fibrosis

denotes excessive deposition of collagen and other ECM components in a tissue

• can impair the function of tissue

what are some undesirable consequences of wound healing?

1. keloids

2. contractures

3. adhesions

4. strictures

keloid

excessive collagen production causing protuberant scar

-do not regress over time

contractures

scar bridging a joint and restricting motion

adhesions

organized exudate bridging serosal surfaces

band of scar tissue that joins tow internal body surfaces that are not usually connected

strictures

circumferential scar in a tubular structure