Healing By Primary Intention

Question 1

What occurs during seconds - minutes of injury?

Answer 1

Haemostatsis.

Severed arteries contract -> Narrow space fills with clotted blood -> Dehydration of surface clot and scab forms, acting as a natural dressing.

Question 2

What happens within minutes to hours of injury?

Answer 2

Inflammation - Triggered automatically without waiting for bacteria.

Neutrophils appear at margins to ward off bacteria.

If a wound is kept sterile, the leukocyte count is not high enough to to be considered pus.

Question 3

What happens before 48 hours after injury?

Answer 3

Migration of Cells.

Macrophages appear and scavenge dead neutrophils -> Secrete cytokines to attract cells like fibroblasts and endothelial cells -> Basal epidermal cells meet in middle underneath scab

Question 4

What happens three days after injury?

Answer 4

Regeneration.

Macrophages replace neutrophils -> Granulation tissue (fibroblasts and new capillaries) invade space -> Epithelial cells proliferate, thickening epidermal layer -> Epidermal cells undermine scab so it falls off -> Angiogenesis progresses

Question 5

What happens 7-10 days after injury?

Answer 5

Early scarring.

Wound is filled with fibres which form a fibrous mass -> epidermis keratinises but skin appendages don’t form -> White cell infiltrate, oedema and increased vascularity disappear.

Question 6

What happens 1 month - 2 years after injury?

Answer 6

Scar maturation.

Scar has many collagen fibres, few cells and few elastic fibres so little recoil -> As capillaries disappear, old scars appear white.