Tissue repair

What does tissue repair depend on

Key factors

• Ability of the tissue to divide

• Nutrition

• Severity of the wound

Minor vs Major Wounds

Minor wounds

• Involve only the epidermis

Major wounds

• Involve both epidermis and dermis

List the three stages of tissue repair

• Inflammation

• Organisation/proliferation

• Maturation/remodeling

Summary of what happens in inflammation

• Initial response to injury

• Prepares the area for repair

Summary of what happens in organisation/proliferation

• New tissue and blood vessels form

• Wound begins to fill and rebuild

Summary of what happens in maturation/remodeling

• Tissue strengthens

• Collagen reorganises

• Final repair and restoration of function

What is the purpose of inflammation

• Prepares the wound for repair

• Eliminates invading microorganisms

• Removes debris and dead tissue

What triggers inflammation

Damaged cells release inflammatory chemicals

• These chemicals initiate the inflammatory response

What happens to blood vessels

Increased permeability

• Fluid moves into the wound area carrying:

Macrophages → engulf debris & microorganisms

Clotting proteins → form a blood clot to:

• Stop blood loss

• Hold wound edges together

• Prevent further microbial invasion

Signs of inflammation

• Redness

• Pain

• Heat

• Swelling

What forms on the surface

A scab

• The clot dries and forms a protective scab

What is the purpose of the proliferative stage

• Synthesis of extracellular matrix, including collagen

• Restores blood supply to the wound

What replaces the blood clot

Granulation tissue

• Soft, pink tissue that fills the wound space

• Indicates active healing

What is granulation tissue composed of

Capillaries

• Grow across the wound

• Restore blood supply

• Bring oxygen and nutrients needed for healing

Fibroblasts

• Produce collagen fibres

• Bridge the gap in the wound

Macrophages

• Engulf cell debris

• Remove invading microorganisms

• Clear the blood clot

What do epithelial stem cells do in this stage

Epithelialisation

• Stem cells multiply

• Migrate over granulation tissue

• Begin to restore the epidermal surface

What is the purpose of the maturation stage

• Completes permanent skin repair through:

• Regeneration

• Fibrosis (scar formation)

What happens to collagen

Collagen remodelling

• Collagen is reorganised and tightened

• Helps pull wound edges together

What happens to granulation tissue

Replacement with scar tissue

• Existing blood vessels are compressed

• Granulation tissue is replaced by scar tissue → fibrosis

Properties of scar tissue

• Avascular

• Tough

• No elasticity or flexibility

• No hair follicles

• No sweat or oil glands

When does regeneration occur

If damage is minor OR epidermal stem cells are present

• Stem cells multiply under the scab

• Regenerate the epidermis

• Scab falls off

• Skin returns to pre‑injury appearance

When is scar tissue visible

Visible scar

• If repair occurs only by fibrosis

• Common in major wounds

Invisible or minimal scar

• If repair occurs by regeneration + fibrosis