Skin Wound Healing Flashcards
Define ‘repair’
Restoration of tissue structure and function after an injury. Regeneration and scar formation contribute in varying degrees.
Define ‘regeneration’
Replacement of normal tissue components and return to a normal state
Define ‘healing’
Results in scar formation if the tissues are incapable of complete restitution OR the supporting structures are severely damaged
What does repair require?
Cellular proliferation (epithelium, fibroblasts, stem cells), cellular interactions, cellular/EC interactions.
What are the 2 types of stem cells and where are they found in the skin?
- Found in the epidermal basale layer in bulb of hair follicle
- Transit amiplifying/prgenitor cells (TA) and stem cells (SC)
- Rapidly dividing TA cells take care of daily maintenance. Have a small and short lived contribution to wound healing
- Slow cycling SC make a greater and more sustained contribution
What is the role of the ECM?
- Mechanical support for tissues
- Substrate for cell growth and formation of tissue micro environments
- Regulates cell proliferation and differentiation
- Scaffolding for tissue renewal
- Storage and presentation of regulatory molecules
What are the 2 main types of skin wounds?
- Ulcer - severe injury resulting in complete loss of the surface, including the basement membrane. Heals from the bottom up and results in scar formation
- Erosion - mild, superficial injury to epidermis. The basement membrane remains intact
What are the phases of wound healing?
- Inflammation
- Granulation tissue formation
- Scar formation
Describe how wounds heal
- Inflammation
- neutrophils migrate to the site of injury, followed by macrophages
- lasts for about 3 days
- Formation of granulation tissue
- angiogenesis occurs from pre-existing vessels to increase blood flow to area
- tissue repair begins within 24hrs
- granulation tissue forms by 3-5 days via angiogenesis and fibroblast migration and proliferation at the site of injury. ECM is also deposited
- tissue has a soft, pink, granular appearance
- tissue is arranged with fibroblasts perpendicular to the blood vessels
- often oedematous, oedema can persist long after acute inflammation has resolved
- Scar formation
- granulation tissue gradually accumulates collagenous (EC) matrix which acts as a scaffold for the formation of scar tissue
- As healing progresses, the numbers of proliferating fibroblasts decreases and vascular regression occurs which gives scars a pale appearance
Draw a graph to show the phases of wound healing
What kinds of wounds heal by first intention?
Clean, uninfected surgical incision closed with sutures
How do wounds heal by first intention/primary union?
- Neutrophils migrate to fibrin clot, followed by macrophages
- Basal cells at cut edge of epidermis begin to show mitotic activity
- Epithelial cells migrate and proliferate across the dermis, depositing BM as they go. Meet in the middle under a scab. Epidermis thickens (hyperplastic)
- Fibroblasts migrate, proliferate and produce collagen. Angiogenesis occurs and granulation tissue forms
In early weeks:
- collagen continues to accumulate
- fibroblasts decrease in number
- leukocytes, oedema and vascularity decreases
Months to a year:
- scar forms - dense CT covered by normal epidermis
- dermal appendages that were destroyed (hair follicles) permanently lost
In what situation would healing by second intention occur?
Extensive tissue loss, dirty wound e.g. abscess, ulceration, larger wounds.
How do wounds heal by second intention?
- Same as by first intention except granulation tissue formation is rapid and lasts 1-2 weeks
- As granulation tissue is former, epidermis proliferates and a necrotic slough is formed (prevents inflammation and healing)
- A zone of hyperaemia occurs below the granulation tissue due to vascular regression. Ischaemic damage causes necrosis
- Granulation tissue maturation and wound contraction occurs for 2-6 weeks
- Granulation tissue contracts, pulling the edges of the wound together. Epithelial proliferation occurs accross the granulation tissue before the scab is shed
- Results in a pale, depressed scar with surrounding puckering caused by wound contraction
Draw graphs to show how wound healing differs between horses and ponies
