Wound Healing Flashcards
What is different about the skin blood supply in cats and dogs vs humans?
The presence of direct cutaneous vessels as opposed to perforating musculocutaneous vessels
What does The presence of direct cutaneous vessels in cats and dogs allow?
Elevate and mobilise large skin flaps.
What is key to preserve to create a successful skin flap?
Preservation of the deep dermal plexus
In full thickness skin wounds, what is the source of epithelial cells which cover the wound?
stratum germinativum
What are the epidermic hair bearing areas?
stratum corneum and the stratum germinativum
The hypodermis is below the dermis.
What does this contain. How does it differ in the head, neck and trunk.
Adipose tissue and loose connective tissue
A thin panniculus muscle is present in the head,neck and trunk
How is the skin supplied with blood?
Direct cutaneous vessels which run parallel to the skin within the hypodermis.
What do the terminal branches of the direct cutaneous vessels form?
A rich capillary plexus - deep dermal (/ subdermal) plexus
In areas of skin with a panniculus muscle, where does the subdermal plexus run?
Above and below panniculus muscle
What is the main collagen type in skin?
Type 1
The skin is viscoelastic and exhibits hysteresis, what is this?
The stress-strain curve is non-linear.
What is mechanical creep? What causes this in skin?
The skin undergoes time-dependent plastic strain while under constant stress, meaning it is stretched beyond its inherent extensibility.
Thought to be due to the realignment of collagen fibres.
What is stress relaxation? What is it thought to be due to?
a decrease in the level of stress under the same amount of strain.
The breakage of collagen fibres and permanent plastic strain. Breakage of elastin fibres leads to a loss of the skin’s elastic recoil under constant strain.
When does first intention healing occur?
when the wound edges are sutured.
When does second intention healing occur?
When there is tissue loss and the wound edges cannot be apposed. This type of healing is also referred to as open-wound healing.
When does third intention healing occur?
When there is a delay in closing the wound, typically because of concerns about infection or devitalisation.
What chemical is release by cells in wounds?
Cytokines
What functions do cytokines have? (3)
- Autocrine
- Paracrine
- Direct the synthesis of compounds for wound healing
What are the 3 phases of wound healing?
- Inflammatory
- Proliferative
- Maturation and remodelling
What are the key steps of the inflammatory phase? (3)
- Haemostasis
- Recruitment of inflammatory cells into the wound
- Debridement.
Inflammatory phase:
What does a blood clot contain? and what is it the basis for?
Fibrin and fibronectin
Basis of the provisional extracellular matrix
Inflammatory phase:
What does the provisional extracellular matric allow?
Cells t migrate into the wound - ats as a scaffold.
Inflammatory phase:
What do platelets within the clot release and results in (3)?
Vasoactive compounds
- vasodilation, cytokines (chemotactic for WBC)
Inflammatory phase:
How do WBC leave circulation and enter wound? (2)
Margination and diapedesis
Inflammatory phase:
What is the first inflammatory cell at the wound?
Neitrophil
Inflammtory phase:
What do neutrophils release?
What do neutrophils have a role in? (3)
- Proteinases debride necrotic tissue
- bacterial killing (phagocytosus)
- Production of free radicals
What is free radical production reliant on?
Oxygen (hence need for perfusion)
Inflammatory phase;
What happens to neutrophils after a few days?
Apoptosis
Inflammatoty phase:
What cell follows neutrophils?
Monocytes
Inflammatory phase:
What is the role of monocytes? (3)
- Phagocytosis
-Wound debridement, - Produce cytokines which are chemotactic for proliferative stage
What is the primary cell in wound within 48-96 hours?
monocytes
… are responsible for activation of the clotting cascade, formation of the provisional extracellular matrix and release of chemotactic cytokines.
Platelets
… are responsible for debridement of necrotic tissue and bacterial killing.
Neutrophils
.. are the dominant cell in the wound by 48-96 hours and have a role in wound debridement and the recruitment of cells involved in the proliferative phases of wound healing.
Macrophages
What days of wound healing is the proliferative phase?
5-20
What is the hallmark of the proliferative phase?
Granulation tissue
What does granulation tissue contain? (4)
Macrophages
Fibroblasts
Capillary buds
A ground substance.
What 4 processes are involved in proliferative stage?
Angiogeneis
Fibreoplasia
Epithelization
Wound contraction
What does angiogenesis develop in result of? (2)
Growth factors
Wound factors e.g. Low O2 tension
Proliferative phase:
What is fibroplasia?
Fibroplasia is the proliferation of fibroblasts at the margin of the wound and their migration across the fibrin scaffold of the wound bed.
Proliferative phase:
What do fibroblasts produce to aid migration? (2)
Proteolytic enzymes:
Plasminogen activator Matrix metalloproteinases (MMPs)
Proliferative phase:
What do fibroblasts initially produce to form a loose extracellular matrix?
Fibronectin
Proliferative phase:
Following the production of fibronectin, what is produced following this? (round 4-5 days after wounding)
Collagen type III
Why is the production of collagen type III a critical period of wound healing?
Wound gains tensile strength
How long does the fibroblastic phase of proliferative phase last?
2-4 weeks
After fibroplasia phase (proliferative phase); the fibroblasts and capillaries decrease - what is then complete?
Net collagen synthesis
What is epithelialisation?
Epithelialisation is the restoration of an epithelial surface.
When does epithelialisation begin?
1-2 days
Epithelialisation (proliferative):
What is the source of epithelial cells:
A) full thickness wounds?
B) Partial thickness wounds?
A) Wound edges
B) Dermal adnexa
In a sutured wound, how long does it take for a small dermal gap to bridge? (Epithelialisation)
48 hours
Wound contractions (proliferation phase):
What happens to the fibroblasts?
Fibroblasts within the wound develop smooth muscle properties and become myofibroblasts.
When does wound contraction start?
Days 5-8
When does wound contraction decline?
6 weeks
After how long does The wound does not support further epithelialisation or contraction and becomes a chronic granulating wound
2-4 weeks
… is the formation of a new capillary network across the wound.
Angiogensis
… is the proliferation of fibroblasts and the production of type III collagen, which provides early wound strength.
Fibroplasia
… is the mobilisation and migration of epithelial cells across the wound to restore an epithelial surface.
Epithelialisation
… is the centripetal movement of the skin edges to shrink and close the wound.
Contraction
What is the main aim of the matruation and remodelling phase?
Strengthening collagen
Collagen type III to type I
Maturation and remodelling phase - Collagen degradation by collagenase enzymes is balanced by?
Tissue inhibitors of metalloproteinases (TIMPs)
Net collagen synthesis:
A) When is it complete after injury?
B) How long does maturation continue for?
A) 4-5 weeks
B) 12-18 weeks
What is the wound strength of skin ay 10-14 days?
5-10%
What is the wound strength at 3months?
80%
What is the wound strength at 3-4 weeks?
25%
What is pseudohealing?
Sutured wounds appear healed once epithelialisation is complete. However, they may not yet have gained enough tensile strength to guarantee apposition once skin sutures are removed. = dehiscence
What is the difference between dog and cat wound healing at 7 days?
Feline sutured wounds have been shown to be slower to heal, being only 50% as strong
Why is a cat wound slower to heal?
Lower cutaneous perfusion in the first week after surgery, followed by a more rapid gain during the second week
What is different with cat granulation vs dogs?
Cats produce less granulation tissue than dogs, with a peripheral rather than central distribution.
What was the difference in wound area by contraction/epithelialisation over 21 days?
Reduction greater in dogs
How do dog wounds close?
Central pull and epithelization
How dog cats wounds close?
Contraction of wound edges
In both cats and dogs, it is important to preserve ……. in second intention healing, but less so in first intention healing.
Subcutaenous tissue
What are the layers of the GI tract? (4)
Mucosa
Submucosa
Musularis propria
Serosa
What collagen does submucosa of GIT contain?
I
II
V
What layer provides tensile strength to GIT
Submucosa
During GIT closure, why must we not over tighten sutures? (we should anticipate)
Anticipate oedema which occurs in the mucosa and submucosa layer
During GI closure, what forms rapidly at the outer serosal layer providing the watertight seal?
Fibrin seal
During GIT healing, what produces collagen in the proliferative phase? (2)
Fibroblasts
Smooth muscle cells
When is wound breakdown of GIT most likely to happen?
days 2-5
In terms of healing phases, why is GIT dehiscence most likely to happen day 2-5?
Collagen lysis during the inflammatory or lag phase results in a net loss of wound strength.
After day 2-5 of GI wound - what is gained?
tensile strength
What factors affect GIT wound healing? (3)
- shear stress due to increased intraluminal pressure during peristalsis and transport of ingesta;
- the presence of aerobic and anaerobic bacteria;
- adequate oxygen delivery.
How long does re-epithelialisation take following injury of uroepithelial cells?
2-4 days (there is a rapid increase in mitotic activity)
How long does it take for collagen synthesis to reach its peak in the urinary bladder post surgery?
5days
How long does it take for the urinary bladder to regain 100% of its unwounded strength?
21 days
After surgery - how long does it take for the urinary bladder collagen synthesis to return to normal?
70 days
Why is the fascial healing inflammatory phase prolonged?
This is thought to be due to the longer distances cells must migrate to reach the relatively avascular and acellular wound edges.
How long do fascial wounds have no inherent strength for?
7 days
What does fascial wound strength depend on?
Suture material
What is the wound strength of a fascial wound after 3-4 weeks?
50%
Fascial wound:
Where should sutures be placed in relation to wound edges?
3mm
Why should sutures avoid 3mm from edges of fascia wounds?
There is a zone of collagenolysis and matrix degradation at the wound edges.
What systematic factors DELAY wound healing? (4)
- Poor immune function
- Chemotherapy
- Radiotherapy
- Age
Name local factors which impact wound healing (5)
- Wound perfusion
- Necrotic tissue/Foreign material
- Haematoma/seroma
- Bacteria contamination
- 1ry wound closure if preferred to 2ry
