Wound Healing

Question 1

What are the 3 phases of wound healing?

Answer 1

Inflammatory, proliferative, and remodeling

Question 2

When does the inflammatory phase start and how long does it last?

Answer 2

Starts within 6-8 hours and it lasts 3-4 days

Question 3

What are the major steps of the inflammatory stage?

Answer 3

Platelets come to the site of wound first and release factors –> Fibrin is the first ECM component that gets deposited, vasodilation occurs, the influx of neutrophils within the first 48 hrs, macrophages arrive after neutrophils and aid in phagocytosis debride and preparing for proliferative phase

Question 4

What factors do platelets release at the site of a wound?

Answer 4

ADP, clotting factors, PDGE, EGF, fibrinogen, fibronectin, TGFalpha, and TGFbeta

Question 5

What is the role of fibrin and fibronectin in wound healing?

Answer 5

Fibrin is the first ECM component deposited and fibronectin helps provide the matrix for fibroblasts to rebuild. Also, essential to the poress of clotting and coagulation

Question 6

What is the role of the neutrophils in wound healing?

Answer 6

They are attracted by fibrinogen/fibrin products, C5a, and other cytokines and they are involved in the clearance of bacteria and debridement

Question 7

What cells are absolutely required for wound healing?

Answer 7

Macrophages

Question 8

What is the role of macrophages in wound healing?

Answer 8

Secrete growth factors, set the stage for proliferative stage (growth factors increase fibroblasts and ECM development)

Question 9

When does the proliferative phase start?

Answer 9

Starts between 5-7 days after initial wound

Question 10

How long does the proliferative phase usually last?

Answer 10

May last up to 1 month

Question 11

What broad events occur during the proliferative phase?

Answer 11

Reepithelializiation (starts within 24 hrs), the formation of granulation tissue (3-5 days), fibroplasia (3-14 days), wound contraction (myofibroblasts 1-2 weeks), neovascularization/angiogenesis (starts the first week)

Question 12

What factors mediate reepithelialization?

Answer 12

EGF, KGF, IGF-1 and other growth factors

Question 13

How do keratinocytes migrate into wound bed?

Answer 13

Keratinocytes from adjacent skin “leapfrog” over each other. This is done via the breaking down of desmosomes and lateral mobilization. Collagenases produced by macrophages help with this migration

Question 14

What is granulation tissue made up of and is its purpose?

Answer 14

Macrophages, fibroblasts, and vessels –> deposits extracellular matrix scaffolding for repair.

Question 15

What molecule is required for granulation tissue and what ultimately replaces it?

Answer 15

Fibronectin is required for granulation tissue formation and it is later replaced by type III and I collagen

Question 16

What happens during fibroplasia?

Answer 16

Deposition of collagen and other ECM components by fibroblasts (they migrate in 2 days after wond creation and require the fibronectin framework for migration/travel). Myofibroblasts also help contract the wound

Question 17

What occurs during the remodeling phase?

Answer 17

Scar matrix formation by fibroblasts (produce collagen/fibronectin/hyaluronic acid) and region of granulation tissue (endothelial cells are first to undergo apoptosis and macrophages are last; then collagen remodeling

Question 18

What is scar strength at 1 week, 2 weeks, 4 weeks, 3 months, and 1 year?

Answer 18

1 week = 5%

2 weeks = 10%

3 weeks = 20%

3 months = 50%

1 year = 80%