Flashcards in Tissue repair and Wound Healing Ch.3 Deck (83):
continuously dividing, never enter G0 phase
- surface epithelia, skin, oral cavity, GI tract, uterus
- mature cells derived from adult stem cells
- bone marrow stem cells
stable tissues, resting in G0 phase
- low level of replication
- liver, kidneys, pancreas, smooth mm
- stem cells in sebaceous glands
- almost never divide, always in G0
- neurons and skeletal and cardiac mm.
totipotent stem cells
- seen in early development of embryo
- can make every tissue of the body as well as placenta
pluripotent stem cells
- found in embryo within inner cell mass of blastocysts
- can be taken from embryo and cultured to form any adult tissue
found in fetus and adult
- make several different cell lines
- ex. stem cells found in bone marrow
lineage committed SC
- close to final differentiation
induced pluripotent SC (iPS cells)
differentiated cells that can be turned into ES cells by transduction of genes encoding ES cells transcription factors
a) non-stem cell transforms into a different type of cell (similar to metaplasia)
b) already differentiated stem cell creates cells outside its already established differentiation path
a) Genes from a host cell (a bacterium) are incorporated into the genome of a bacterial virus (bacteriophage) and then carried to another host
what are the major SC's found in bone marrow?
1. Hematopoietic Stem cells: HSC’s
i. Generate all of blood cell lineages
ii. Can reconstitute bone marrow
2. Marrow Stromal Cells: MSC’s
i. Multipotent cells that can generate chondrocytes, osteoblasts, adipocytes, myoblasts and endothelial cell precursors
ii. Can migrate to tissues and generate stromal cells
what SC's are found in liver?
Oval cells: located in the canals of Hering aka “biliary duct system”
i. Bipotential progenitors capable of making hepatocytes and biliary cells
ii. Only function when the hepatocyte proliferation is blocked: results in compensatory neoplasia
SC's found in brain?
Neural stem cells: NSC's
i. Can regenerate neurons, astrocytes, and oligodendrocytes
ii. Found in dentate gyrus and subventricular zone
SC's found in skin?
a. Skin stem cells:
i. Located at hair follicle bulge, interfollicular areas and sebaceous glands
ii. Differentiate into epidermis
iii. Stimulation signals from Wnt pathway
SC's in intestines?
a. Intestinal stem cells:
i. Found in crypts
do skeletal and cardiac muscles divide?
skeletal mm. myoctyes don’t divide after injury. Growth and regeneration of mm. occurs by replication of satellite cells
a. Limbal Stem cells: LSCs
i. Located in b/w epithelium of cornea and conjunctiva
ii. Regenerate the cornea
what is the cell cycle?
G0= resting phase
G1=growth in mass
S= chromosome duplication
G2= continued growth
checkpoints of cell cycle?
G1/S checkpoint: monitors the integrity of DNA before replication
G2/M checkpoint: checks DNA after replication
- Progression through these checkpoints is tightly regulated by CDK’s and RB protein
- CDK inhibitors prevent progression through the cycle when DNA damage is sensed
- If DNA damage is too severe then cells are apoptosed or placed in a state of “senescence” through p-53 mechanisms.
3 types of signaling?
1. autocrine: cells signal to themselves
2. paracrine: cells signal to neighbors
3. endocrine: signal sent to distant targets
a chemical substance that encourages a cell to commence cell division, triggering mitosis.
Platelet derived growth factor (PDGFβ)
***brings inflammatory cells in!
- activates fibroblasts, smooth muscle cells, and monocytes
for their proliferation and migration
- also stimulates angiogenesis and wound contraction
Fibroblast Growth Factor (FGF)
- mitogenic for most mesenchymal cells
-induces endothelial cell to release proteolytic enzyme
***chemotactic for fibroblasts
- stimulates angiogenesis
***wound contraction and
** wound repair
epidermal growth factor (EGF)
- mitogenic for epithelial cells, fibroblasts, glial cells
and SMC (important in skin)
****stimulates granulation tissue formation
Transforming Growth Factor (TGFβ)
* TGFbeta is most important fibrogenic agent - causes fibroblast migration and proliferation and increased collagen synthesis
- alpha TGF : simulates replication of hepatocytes and epithelial cells
- Beta TGF acts as either a growth stimulator or a growth inhibitor (does many different things)- chemotactic for PMNs
Vascular Endothelial Growth Factor (VEGF)
- central role in the growth of new blood vessels
- increases vascular permeability
cytokines important in healing?
***IL-1 and TNF *** induce fibroblast proliferation
and collagen synthesis.
- TNF can also stimulate angiogenesis. (activates macrophages)
what causes monocyte chemotaxis?
FGF = chemotactic for fibroblasts
TGF-Beta = chemotactic for PMNs
growth of new vessels: VEGF!
pathways, what do cytokines bind? growth factors?
growth factors: bind receptors with intrinsic tyrosine kinase activity (PI3 kinase pathway, MAP-kinase, IP3 pathway)
cytokines: bind receptors without intrinsic tyrosine kinase activity (JAK/STAT pathway)
* note: most things bind GPCR's, initiating a CAMP pathway
regeneration vs. compensatory hyperplasia
- Regeneration = constitution of original form
- Compensatory Hyperplasia = restoration of physical mass
-The liver is “regenerated” after partial hepatectomy not through true regeneration (which would result in the same size and shape of lobes as previously) but through compensatory hyperplasia.
-compensatory hyperplasia results in the growth by enlargement of the lobes that remain after the operation- resulting in the restitution of functional mass rather than the reconstitution of original form
injury to hepatocytes and injury to hepatocyes/matrix
The extracellular matrix is very important for regeneration and repair. If this is damaged then it results in scarring.
→ Injury to Hepatocyte cells: Regeneration occurs
• Leads to proliferation of residual cells within the intact matrix. Tissue remains organized
→ Injury to Hepatocyte cells AND matrix: Repair by scarring occurs
•Leads to deposition of CT: proliferation of residual cells within the disrupted matrix
•Will see nodular regeneration
•Fibrous structural proteins confers tensile strength.
* elasticity *
•Provides the ability to recoil and return to a baseline structure after physical stress.
•needed in blood vessels, lungs, etc.
**DIFFUSE STROMA, fills in gaps
• Helps regulate ECM structure and permeability
• Modulate cell growth & differentiation
• Maintain cell morphology
* ON CELL SURFACE, attachment to outside stroma
• Include fibronectin, laminin and vitreonectin.
• Link ECM components to cells via cell surface integrins.
* ADHESION and Mechanical signaling
• A family of cell surface receptors mediating adhesion of cells to ECMs
cadherins and integrins link the cell surface with the cytoskeleton through binding to actin and intermediate filaments
how does signaling through matrix proteins occur?
- Integrins bind things to the matrix, thus if the matrix is pulled, then it can induce mechanical signaling through the integrins. They will initiate the production of intracellular messengers that can directly mediate nuclear signals.
- Syndecan: signals pulling and stretching of the basement membrane, attached to actin cytoskeleton
- Hyaluron chains: located on cell surface and can stimulate the cell through mechanical transduction
what is BM mostly made of?
Basement Membrane is mostly Collagen Type IV, with large amounts of proteoglycans!
Collagen Type I
tendons and bones
o found in hard and soft tissues
o defects with osteogenesis imperfecta
Collagen Type II
type II: found in cartilage
Collagen Type III
present in hollow organs and soft tissues, necessary for repair but eventually replaced by Type I
Collage type IV
found in basement membrane
Collagen type VII
important in the skin – anchors dermal-epidermal junction
INDUCED BY VEGF (also can be induced by HIF and TGF)
1. Proteolytic degradation of basement membrane
2. Migration of endothelial cells
3. Proliferation of endothelial cells
**Angiogenesis can result from pre-existing vessels or can result from mobilization of EPC’s from the bone marrow. Regardless of initiating mechanism, vessel maturation involves the recruitment of pericytes and smooth muscle cells.
important for lymphatic proliferation
how are tip cells stimulated?
VEGF drives tip cells and tells cell to continue replicating
NOTCH tells neighbor via paracrine signaling to be done growing
-Tells tip cell to STOP replicating, allows vessels to mature
-decreases sprouting and EC proliferation
-increases vessel lumen size and vascular organization
-Tells tip cell to GO ahead with replicating, growth of new vessels
-Increases sprouting, EC proliferation and survival
-Decreases vascular organization
6 steps to wound healing?
1. formation of blood clot
2. formation of granulation tissue
3. cell proliferation and collagen deposition
4. scar formation
5. wound contraction
6. CT remodeling
-Appears soft, pink and granular
-Large amount of collagen producing fibroblasts
-New-thin walled capillaries (angiogenesis)- VEGF
-Inflammatory cells in a loose ECM with edema
-This forms when repair by parenchymal regeneration cannot be accomplished
-Granulation tissue acts as a scaffolding for Epithelial cells to proliferate across
-Eventually epithelium is regenerated and Granulation tissue is removed, however there will always be a small amount of scarring
- stimulated by EGF
roles of granulation tissue?
-Anti-infection and protection of wound
-Filling incision or wound
-Replacing necrotic tissue, effusion
-Vessels provide conduit for nutrients for cells
how does cell proliferation and collagen deposition occur?
-Fibroblasts: divide and secrete collagen (Initially collagen in wounds is type III, then becomes Type I)
- stimulated by FGF
-Eventually results in fibrosis with CT matrix
-Scar tissue is pale and avascular tissue
-Composed of collagen, fragments of elastic tissue, ECM and inactive fibroblasts
-Advantages: provides a resilient permanent patch and provides tensile strength of tissue after healing
- see massive amounts of collagen layed down in scarring
-Occurs due to myofibroblasts that are layed down
-Greater with second intention wounds
how do macrophages debride and remove injured tissues?
Primary Union/ First Intention:
-Approximation via suturing
-Will see little angiogenesis, little fibroblast deposition, small granulation, will have very little evidence of a scar
-Heals nearly completely in weeks
-Can be accomplished with surgical sutures or surgical glue
steps of healing first intention:
•Clotting—contact with collagen & tissue factors from injured cells
•Thrombin—attracts macrophages and --> fibroblast replication
•Degranulation of platelets --> PDGF= growth factor, mitogen &
chemotaxin for fibroblasts
•Scab formation: clotting and dried clot
•Contracts wound by shrinking (dehydration)
•Migration of cells (within 24 hours) – inflamm. cells and fibroblasts
•Regeneration (3 days) – fibroblastic proliferation
•Early scar (7-10 days) – nearly healed
•Scar maturation (1 month-2 years)
Secondary Union/ Second Intention:
-Healing of a large wound
-Large amount of granulation tissue, scar tissue, and wound contraction. Lots of angiogenesis.
-Debridement may be necessary
-Myofibroblasts: needed to contract he wound along with fibrin
-Inflammation is more intense because there is more necrotic debris, exudate and fibrin to remove
-Fibrin deposition seals the wound
-Scab plus epithelial layer are re-instated and the wound heals while granulation tissue remains
necessary for wound contraction, needed in secondary union wounds!
Vitamin C deficiency
inhibits collagen synthesis and retards healing
results in delayed healing
inadequate blood supply, results in decreased healing
have anti-inflammatory effects and inhibit collagen synthesis
an exaggeration of contraction usually seen with burns
excessive scar formation, that extends beyond original injury.
"proud flesh" or "exuberant granulation"
- excessive granulation that blocks re-epithelialization
when sutures break or pull through the skin and results in skin separation. Comes from primary intention, turning into secondary intention
when the sutures are lost and the deeper viscera protrudes through the wound
what cytokines drive scarring?
IL-1, IL-4, IL-13
what leads to fibrosis? chemokines responsible?
- persistent stimulation and chronic inflammation lead to activation of macrophages
- macrophages secrete growth factors (PDGF,FGF, TGF-B) which results in proliferation of fibroblasts, endothelial cells and fibrogenic cells
- macrophages secrete cytokines (IL-1, 4, 13) which results in increased collagen synthesis
- there is decreased metalloproteinase activity, resulting in decreased collagen degredation
- all of these things result in fibrosis
Deposition of collagen is enhanced by decreased activity of metalloproteinases: which breakdown the collagen. These proteins are often seen in the beginning of healing when protein needs to be removed.
alpha 1 antitrypsin
is produced in liver and functions to protect the lungs from neutrophil elastase, an enzyme that can disrupt CT.
- genetic disorder that causes defective production, leading to decreased A1AT in the blood and lungs, and deposition of excessive abnormal A1At protein in liver cells. This causes emphysema or COPD, as well as liver disease.
- normal blood levels of a1at vary, but with this deficiency it is very low.
- develop liver cirrhosis b/c its not being excreted properly
- Cigarette smoke is very harmful for these individuals because it increases the inflammatory reaction in the airways, and attracts neutrophils, further damaging the lung’s elastase.
what do you see with A1AT deficiency?
-On CXR, see widened chest, decrease in tissue = emphysema
-Ultrasound of gallbladder = gallstones
-Liver ultrasound = see fibrosis
-ALT/AST is elevated = hepatic necrosis/inflammation
-Pulmonary function tests decreased
-Liver biopsy looks nodular: regenerative hepatocytes (due to destroyed scaffolding of liver)
phenotype of A1AT deficiency? what accumulates?
- results in alpha-1-antitrypsin-z building up
- this is an abnormal protein inclusion and will result in setting off caspase C and leading to apoptosis
- necrosis is also seen, which leads to inflammation and fibrosis of the liver
- accumulation of mutant 1ATZ in the ER results in activation of the caspase cascade both via the ER and mitochondrial pathways
- autophagy will occur and will see residual bodies in this disease
- phagosomes induce cell necrosis
- necrosis leads to repair process, new hepatocytes form from oval cells
- development of regenerative nodules, continued stimulation can lead to DNA damage and neoplasia
- see repair with scarring (cirrhosis) due to fibroblast proliferation and collagen deposition
- can see panniculitis (fat necrosis) with diffuse plaques on the extensor surfaces
major remodeling protein from macrophages
MMP and collagenases
what can inadequate formation of granular tissue or assembly of scar lead to?
wound dehiscence and ulceration
what is the most important fibrogenic agent?
- causes fibroblast migration and proliferation, increased collagen, and decreased degredation of ECM due to inhibition of MMPs