06: Wound Healing

Types of events that make up wound healing

• Physical

• Chemical

• Cellular

Three stages of wound healing

• Inflammatory/lag

• Proliferative

• Maturation and remodeling

Purpose of the inflammatory phase

• Eliminate microorganisms

• Neutralize irritants

• Promote removal of dead/dying tissue (debrides itself)

What determines how much inflammation is produced by a wound

The degree of the insult

How long is the inflammatory phase of wound healing

0-5 days

Purpose of the increased vascular permeability that happens during the inflammatory phase of wound healing

Allows chemotaxis of circulating immune cells and release of cytokines and growth factors

Why does a wound open directly after it happens

Muscle pull

Purpose of hemorrhage during the inflammatory phase

• Fills the wound

• Cleanses the wound

• Provides cells for debridement

Physiologic events that stop hemorrhage from a wound

Small blood vessels constrict and a thrombus/clot forms

Functions of the clot other than hemostasis

• Localizes inflammation

• Glues wound edges

• Scaffold for cell migration

Processes that allow for WBCs to get from circulation to the site of a wound

Margination and diapedesis

First inflammatory cell on the scene during cellular wound debridement

Neutrophils

Second inflammatory cell on the scene during cellular wound debridement

Monocytes → macrophages

Functions of macrophages during cellular wound debridement

Cleans up the wound and remodels via tissue formation and angiogenesis

Function of platelets during cellular wound debridement

• Recruits neutrophils and monocytes

• Produces growth factors

Function of lymphocytes during cellular wound debridement

Arrives with macrophages so they have something to present to

When does the proliferative phase of wound healing start

5 days after the injury (after the 0-5 days of the inflammatory phase)

Three processes associated with the proliferative phase of wound healing

• Fibroblast proliferation

• Capillary infiltration

• Epithelial proliferation and migration

What is the end result of fibroblast proliferation and capillary infiltration during the proliferative phase of wound healing

Granulation tissue

What is produced by fibroblasts during wound healing

Fibrous tissue (collagen, elastin, and proteoglycans)

What mediates the infiltration of capillaries to a wound

Low oxygen tension and chemotactic factors

What does normal granulation tissue look like

Bright red and fleshy with cobblestone appearance

Function of granulation tissue

• Fills the defect from the wound

• A barrier to infection

• Scaffold for epithelialization

• Provides fibroblasts for wound contraction

What type of collagen is initially deposited by fibroblasts

TIII

What type of collagen is eventually left behind to provide wound strength after remodeling

TI

TIII v TI collagen

TIII is disorganized, TI is arranged horizontally with more cross linking

How do skin cells know how to stop growing during the epithelialization part of the proliferative phase of wound healing

Contact inhibition

Cells that mediate wound contraction

Myofibroblasts

Why is wound location and granulation tissue SO important for wound healing

Tension inhibits wound healing

When does the maturation and remodeling phase of wound healing begin

When collagen has been adequately deposited, 17-20 days → years

How much of the wound’s final strength is present after 3 weeks of healing

20%

How much of the original strength can be regained by a wound

80%

Which tissue can regain 100% of its strength after a wound

Bladder tissue

Why is a scar pale

Decreased number of capillaries in the area

Factors that can maximize wound healing (limited list from this lecture)

• Bandages

• Vitamin A

• Oxygen

Function of vit A for wound healing

Used for patients that are on corticosteroids because it reverses the effects of steroids

THE primary and most common factor that delays wound healing in our animals

Foreign bodies