Wound Healing Flashcards
Wound healing, cells are classified by capacity to proliferate.
What are the 3 categories?
- Continuously dividing cells (Labile)
- Quiescent Cells (Stable)
- Non-dividing cells (Permanent)
Cells that divide throughout entire lifespan at regular rate, give rise to more differentiated cells
Labile cells (continuously dividing)
Continuously dividing cells called “labile cells” are also known as what?
Examples?
- “Stem Cells”
- RBCs
- Bone marrow
- Cells of intestine
Type of cells which can easily repair defect in skin wounds or mucosal ulcers
Continuously dividing cells
“Stable cells” -Do not divide regularly, but can be stimulated to divide if necessary
Quiescent cells
Type of cells which form in parenchymal organs: liver or kidneys
Quiescent cells (stable)
Loss of liver parenchyma after a partial hepatectomy stimulates what?
Mitosis of remaining liver cells to replace the loss. Once it has regenerated the cells become stable again and stop dividing
“permanent cells” do not have capacity to proliferate under any circumstances
non-dividing cells
Type of cells which include:
- neurons
- myocardial cells
non-dividing cells
How do myocardial cells repair themselves if they can’t divide?
Fibrous scarring
Neurons (brain cells) is irreversible as they can’t divide, how do they repair?
Gliosis
4 most important cells in wound healing
- Leukocytes
- Macrophages
- Connective Tissue cells
- Epithelial cells
Plays a brief role in scavenging the initial site of injury
PMNs
Stays at site of injury and healing, produces mediators which act on connective tissue
Macrophages
Have hybid properties of smooth muscle cells and fibroblasts
Myofibroblasts
Contracting of these cells occurs within the first few days of healing, reducing defect, holds margins of tissue in close approximation
Myofibroblasts
These cells:
- enable proliferating epithelial cells to cover surface defect
- restore integrity of surface epithelium
myofibroblasts
- Precursors of blood vessels
- Proliferate like sprouts from small blood vessels at margins of wound
Angioblasts
- Appear 2 - 3 days after incision
- By 5th or 6th day, entire field is permeated w/ newly formed sprouts from blood vessels
Angioblasts
Cells that produce most of extracellular matrix including:
- Fibronectin
- Collagen
Fibroblasts
Provide tensile strength to connective tissue matrix and “glue” substances to cells
Fibronectin
Wound initially consists of ___ which is laid down by fibroblasts
Type III collagen (young/immature collagen)
- Most common form of collagen
- replaces type III collagen
- increases strength of all tissues
Type 1 collagen
When does collagen acquire it’s full strength?
- When laid down in extracellular spaces (several weeks after injury)
- When collagen fibers are cross linked w/ each other (dense meshwork)
Healing of sterile surgical wounds occurs by what?
First Intention: site initially contains coagulated blood that forms scab
Scab of sterile incision site is invaded by PMNs, then what?
Macrophages (which promote ingrowth of myofibroblasts, angioblasts, and fibroblasts)
Vascularized connective tissue rich in macrophages and (myofibroblasts, angioblasts, and fibroblasts)
Granulation tissue
Initially the wound contains many myofibroblasts, but they disappear. Initially filled w/ extravasated blood will later become?
Edematous and filled w/ granulation tissue
Composition of matrix changes from Fibronectin and Collagen Type III, to what?
Predominantly Collagen Type I
Final collagenous structure
Scar
Epithelial cells cover margins of the wound within what time period?
3 to 7 days
Granulation tissue filling skin defect in wound is transformed into scar within what time period?
3 to 6 weeks
Sharp, sterile, surgical wounds heal by what?
First Intention (primary union)
Large defects and all infected wounds heal by what?
Secondary intention
Wound contraction cannot be accomplished by myofibroblasts, so granulation tissue remains exposed
Large defects
Wound healing is prolonged, some wounds never completely heal
Secondary intention
Wound healing complicated by local or systemic influences
Delayed wound healing
6 most important determinants of wound healing
- Site of wound (skin heals well compared to brain) 2. Infection (sterile wounds heal faster than infected wounds) 3. Mechanical (margins closed neatly, no movement, no FB) 4. Age 5. Circulatory status 6. Nutrition/metabolism (vitamin C)
- Sluggish formation of granulation tissue in DM patients
- Inadequate collagen production in patients using corticosteroid hormones
Deficient scar formation
Separation of wound margins (occurs in DM patients/corticosteroid use bc/ not enough tensile strength)
Wound dehiscence
Leads to formation of Keloids (hypertrophic scars)
Excess scar formation
Keloids are composed of which type of collagen?
Type III Collagen
