Term
| how are connective tissues classified? |
|
Definition
Based on the composition and organization of
the cells and ECM |
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Term
| what is the structure of bone? |
|
Definition
Cellular component
Extracellular Matrix
glycosaminoglycans, hyaluronic acid,
and water
Type I collagen
Mineralized hydroxyapatite crystals
Ca10(PO4)6(OH)2 |
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Term
| what is the function of bone? |
|
Definition
Site for muscle attachments
framework for skeletal motion
Protection of internal organs
Storage site for calcium and phosphate |
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Term
| what are the two phases of material of bone? |
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Definition
organic phase - weak flexibile material, gives flexibility and resilience.
inorganic phase - strong brittle material, makes bone hard and rigid. |
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Term
| What are the CELLS of bone tissue? |
|
Definition
Osteoblast – bone FORMING
cell
Osteocyte – osteoblast cell that
has become surrounded by
mineralized matrix; sit in
spaces called lacuna; have
extensive cell processes
Osteoclast – bone
RESORBING cells
Osteoprogenitor cell – a resting
cell that can become an
osteoblast with the appropriate
stimulus |
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Term
| what is the osteon/haversian system? |
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Definition
| Fundamental structural unit of bone |
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Term
| what is the coritcal compact bone? |
|
Definition
80% of skeletal weight
Composes the diaphysis in long
bones, surrounds cuboid bones
Laid down in concentric layers |
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Term
| what is cancellous (spongy/trabecular) bone? |
|
Definition
Found at metaphysis, epiphysis of long
bones, in cuboid bones
Thin calcified plates/“struts”: trabeculae
laid down in response to stress
no osteons/Haversian system
Houses red/yellow marrow
Metabolic turnover 8X > cortical bone |
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Term
| how do cortical bone and trabecular bone differ on a stress strain curve? |
|
Definition
| cortical is extremely stiff and extremely strong. Trabecular bone.......????????? |
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Term
|
Definition
Layer of dense connective tissue that
covers outer bone surface except
articular surfaces
Well vascularized to provide blood
flow to bone below through
Volkmann’s canals
Two layers
Outer fibrous layer
Inner cellular layer (contains
osteoprogenitor cells) |
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Term
| what happens when you damage the periosteum? |
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Definition
| early trauma may decrease bone grwoth long term because of the osteoprogenitor cells being damaged. |
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Term
| How does intramembranous ossification work? |
|
Definition
1. Ossification center - Active proliferation of mesenchymal
cells into osteoblasts
2. Osteoid center forms
a. Osteoblasts begin to lay down osteoid (organic part)
b. Osteoblasts retreat or are trapped as osteocytes
3. Woven bone and periosteum form
a. osteoid calcifies to form spicules of spongy bone (form
trabeculae)
b. Increased vascularity
4. Bone remodeling occurs: compact bone |
|
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Term
| how does endochondral ossification work? |
|
Definition
cartilage serves as the precursor
extremity bones and vertebrae
Mesenchymal cells →chondroblasts→hyaline cartilage →
bone
Primary and secondary ossification centers |
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Term
| athletes who may have damage to epiphyseal plates... |
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Definition
| gymnasts can damage these plates a lot and it stops them from growing as much as they were pre-programmed to. |
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Term
| what are the types of bone? |
|
Definition
Immature (Woven) Bone
Not uniform orientation of the collagen fibers
Found in: Embryo and newborn, fracture callus,
metaphyseal region
Mature (Lamellar) Bone
Uniform parallel orientation of collagen fibers
Begins to form 1 month after birth, replaces woven bone
Found in: trabecular lamellae, outer and inner
circumferential lamellae, interstitial lamellae, osteons
with concentric lamellae |
|
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Term
| What is wolff's law of bone? |
|
Definition
Bone is laid down where
needed and resorbed
where it is not needed
Continues throughout life
and adapts to the
mechanical demands
placed on it
Remodeling rates in
trabecular bone >
remodeling rates in
cortical bone |
|
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Term
| How is bone remodeling activated? |
|
Definition
Parathyroid hormone (PTH) and vitamin D trigger
recruitment/activation of osteoclasts and osteoblasts
for greater bone growth
Osteoclasts disappear when resorption is complete |
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Term
| how does resporption of bone work? |
|
Definition
3-12 osteoclasts are needed to cut long resorption
cavities (Howship’s lacunae)
50-100 /day
cuts a hole about 1000-10000 m in length |
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|
Term
Stress fracture – microscopic fissures in bone
50% involve tibia (running/jumping)
25% metatarsals (distal 2nd, 3rd, 5th) 10% fibula, 10% navicular |
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Definition
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Term
| what are the stages of fracture healing? |
|
Definition
| inflammatory phase, reparative healing phase, remodeling phase |
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Term
| what is the time frame of bone healing? |
|
Definition
Stage 1: Inflammation (first 1-2 weeks)
Bleeding from the fractured bone and
surrounding tissue causes the area to swell
(hematoma)
Stage 2: Soft callus (Weeks 2-6)
Pain and swelling decrease, the site of the
fracture stiffens and new bone begins to form
(cannot be seen on x-rays).
Stage 3: Hard callus (Weeks 6-12)
New bone begins to bridge the fracture (can
be seen on xrays).
Stage 4: Bone remodeling (Weeks 12 through
up to 2 years)
The fracture site remodels itself, correcting
any deformities that may remain. |
|
|
Term
| what are the steps of fracture healing |
|
Definition
1.) Inflammatory Phase
Induction (stimulus for bone regeneration) - caused by:
Decreased oxygen, bone necrosis
disruption of & creation of new bioelectrical potentials
Inflammatory response - days 2- 9 following injury:
phagocytes clear necrosed bone
a fibrin mesh forms ,“walls off” fracture, “scaffold”
capillaries grow; arises from periosteum
adult bone usually endosteum; in children periosteum
2) Fibrocartilagenous (soft) callus (FCC) Formation
Fibroblasts produce collagen, osteoblasts produce bone on
outer edges
Serves as a “splint”
3.) Hard Bony Callus Formation & Ossification
Ossification (mineralization) 2-3 weeks through 3-4 months
Alkaline phosphatase secretion (blood serum levels)
In non-Immobilized fractures, more “cartilage” than bone is laid down
must later be replaced by normal cancellous bone
Fractures should be reduced (immobilized) within 3-5 days
4.) Bone Remodeling
Months to years (mechanically stable at 40 days)
Excess material inside bone shaft is replaced by more compact bone
Final remodeled structure is influenced by optimal bone stress |
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Term
| what is the purpose of the bone callus? |
|
Definition
Biomechanical function:
Reduce initial movement and intra-gap
strains so the bone fragments can unite
with bony bridges.
Enlarges cross-sectional area of the
bridging tissue
Increases mechanical stiffness |
|
|
Term
| what are some therapeutic implications for treating fractures? |
|
Definition
Active ROM exercises to joints above and below
immobilized region
Resistive ROM exercises to muscles not
immobilized
Following immobilization:
gentle but progressive resistance exercises of all
immobilized joints
compare to non-injured counterparts (strength
discrepancy < 15% = return to vigorous activity) |
|
|
Term
| what factors affect bone healing> |
|
Definition
Age
Fractured Femur Healing Time
infant: 4 weeks
teenager: 12 to 16 weeks
60 year old adult: 18 to 20 weeks
Early vs late Immobilization
Maximum bone fragment contact
Adequate blood supply/nutrition/hormone levels
Weight bearing exercise for long bones in the late
stages of healing |
|
|
Term
| how does GH affect bone formation/density? |
|
Definition
stimulates protein synthesis/cell growth
dysregulation
pre-puberty (gigantism/dwarfism)
post-puberty (acromegaly) |
|
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Term
| how does thyroxine affect bone formation/density? |
|
Definition
Increases cell metabolism/osteoclast
activity |
|
|
Term
| how do androgens affect bone formation/density? what about estrogen specifically? |
|
Definition
Androgens and Estrogens
Increase osteoblast activity-increase bone growth
faster than epiphyseal cartilage can divide
Cause of growth spurt, eventual closure of
epiphyseal plate
Specifics of estrogen
Initiate faster closure of epiphyseal plate vs
androgens
Stimulate osteoblast activity |
|
|
Term
| how does calcitonin affect bone formation/density? |
|
Definition
Release by C cell of thyroid gland
Decreases osteoclast activity
(decrease bone Ca
2+
release)
Increases osteoblast activity
(increase bone Ca2+ uptake) |
|
|
Term
| how does parathyroid hormone affect bone formation/density? |
|
Definition
Release by parathyroid glands
Decreases osteoblast / increase
osteoclast activity
Increase calcitrol synthesis,
increase Ca
2+
absorption in small
intestine
Decreases urinary Ca2+
excretion, increase phosphate excretion |
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Term
| what does Anisotropic mean? |
|
Definition
| connective tissues respond in different ways depending on the way force is applied |
|
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Term
| what are some of the mechanical factors affecting properties of bone? |
|
Definition
influenced by length, CSA, and amount of
bone tissue around axis
Strain-rate dependent
Other variables to consider
amount of load
number of repetitions
frequency of loading
remodeling process
Repetitive low loads -->
microfracture |
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|
Term
| can muscle contractiion reduce, eliminate, or change tensile stresses on bone? |
|
Definition
| yes, of course! example : glut med affect on femoral head angle. |
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|
Term
|
Definition
“soft bones”
Encompasses many disorders,
osteoid is not mineralized
Insufficient dietary Ca
2+
Insufficient vitamin D/
insufficient sun exposure |
|
|
Term
|
Definition
children’s version of osteomalacia
Increased pathology secondary to
expected bone development
Signs – bowed legs, pelvic/rib/skull
deformities |
|
|
Term
|
Definition
Bone marrow
inflammation
Caused by neutrophil
accumulating (pusforming) bacteria
enters via wound
(compound fracture) or
migration from nearby
infection |
|
|
Term
|
Definition
Reduced bone mass,
architectural deterioration
with increased fragility and
fracture risk
Osteoclastic increase with TNF activity to
produce RANK ligand
(Receptor Activated Nuclear factor B)
Expression of RANK ligand on stromal
cells or osteoblasts binds to
macrophages
CONVERSION OF MACROPHAGES TO
OSTEOCLASTS
Age-related changes in bone density in all
individuals, contribute to development
Peak at mid-30s, loss of 0.7%/yr
PEAK BONE MASSis important
determinant
Hormonal, activity, gender factors –
women at increased risk |
|
|
Term
| what are some causative factors of osteoporosis? |
|
Definition
Hormonal replacement –
Estrogen replacement reduces
bone loss (risks??)
Testosterone may be a factor in
senile osteoporosis
Genetic factors - Vitamin D
receptors (VDR) -decreased
bone density
Mechanical factors – weightbearing
Nutrition – calcium, vitamin D
not well understood |
|
|
Term
| what parts of the skeleton are hyaline cartilage? |
|
Definition
covers the ends of all bones in synovial joints
costal cartilage
forms the structural framework for the larynx,
trachea, bronchi
nasal septum
fetal skeleton |
|
|
Term
| how does hyaline articular cartilage work? |
|
Definition
Bears and distributes loads across a joint
Shock absorber
High water content resists compression well
Increases the area of load distribution
Reduces friction, helps with ease of motion
No intrinsic blood vessels, nerves, or lymph vessels |
|
|
Term
| what is the structure of hyaline cartilage? |
|
Definition
75% water
15% collagen
5% proteoglycans
5% chondrocytes
chondrocytes in lacunae.
ECM = type 2 collagen, water, proteoglycans, glycoproteins. |
|
|
Term
| what are the zones of hyaline cartilage? |
|
Definition
Superficial Tangential Zone -Contains no cells
Middle Zone
Deep Zone
Tidemark
Calcified Cart. -Anchored to subchondral bone |
|
|
Term
|
Definition
Glycosaminoglycans+ Protein core
(GAG’s)
Hyaline cartilage contains
more PG than most joint
structures
Aggrecan
Bound to form large PG
aggregates
Contains GAGs
Chondroitin sulfate
Resists compression
Keratin sulfate |
|
|
Term
| what are some mechanical properties of hyaline cartilage |
|
Definition
Anisotropic material
Viscoelastic tissue
Large elastic region
Returns to former shape
following large
compressive loads.
loads are supported by the
collagen-PG matrix and by
resistance to fluid movement
through the matrix
porous structure
excellent lubricating properties
coefficient of friction is
very LOW |
|
|
Term
|
Definition
| gradual change in shape with a constant load. |
|
|
Term
A woman approximately 60 yrs old is placed on
estrogen replacement therapy secondary to
decreased bone mineral density discovered during
her annual MD visit. Bone mineral density was to
be retested every year for the next 3 years.
Please draw the stress-strain curves of her femur
prior to and following the 3 years of ERT, and if she
had not received the ERT after 3 years.
Why are the curves different . .. Or are they? |
|
Definition
| post ERT curve would still be lower. you are going to lose bone mass, no matter what, but with ERT you lose less bone. rate of bone loss decreases. |
|
|
Term
|
Definition
Degenerative joint disease – degeneration of
articular cartilage
Primary – idiopathic
Secondary – known joint pathology (deformation,
metabolic alterations)
Clinical features
Develop gradually, affect one to few joints
Asymptomatic until > 50 yrs
Symptoms – joint stiffness, deep aching pain > with
repeated use, swelling/effusions |
|
|
Term
| what is the pathogenesis of osteoarthritis? |
|
Definition
Articular cartilage damage
1) Friction-free environment
2) Weight bearing joints
Turnover of chondrocyte
and relation to:
Weight bearing
Genetic factors
Histological features –
fibrillation, erosion |
|
|
Term
| what are some properties of elastic cartilage? |
|
Definition
Has normal components of hyaline cartilage matrix + elastic fibers
•Matrix does not calcify
type 2 collagen. elastic fibers. |
|
|
Term
| what are the properties of fibrocartilage |
|
Definition
Chondrocytes in matrix + dense connective tissue
composed of chondrocytes, Type I (and II) collagen,
and matrix (proteoglycans and water)
found between joints with very little motion
hold joint together, contributes to stability
Type 1 collagen
Combination of dense connective tissue and hyaline cartilage
Resistant to both tension,compression and shear forces
Present at insertion site for tendons and ligaments where
resilience is needed to help absorb sudden physical impact
merges smoothly into the neighboring tissues, typically
tendons or articular hyaline cartilage. |
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