Term
| A 10 year old boy is diagnosed with achondroplasia. What are some characteristics of the disease? |
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Definition
1. long bones are thick and short
2. epiphyseal cartilage is abnormal; poor growth due to inadequate chondrocyte proliferation and early and irregular calcification
3. it is hereditary
- failture of normal endochondral bone formation; most common form of dwarfism
- large head and mid face hypoplasia
- normal appositional bone deposition
- premature growth plate closure |
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Term
What is not true of immature (reticular bone)?
a. lacks compact bone
b. irregular collagen pattern
c. has more cells than mature bone
d. replaces cartilage in long bones
e. lacks osteoclasts |
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Definition
| e. osteoclasts are important in immature bone because resorption occurs to remodel the bone and enable deposition of mature bone. |
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Term
which is not correct?
a. metaphysis - region borders growth plate
b. secondary growth centers - only one per bone
c. osteoclast - stimulation by PTH
d. osteonection - binds Ca and collagen I
e. alkaline phosphatase - hydrolysis of bone inhibitors |
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Definition
| b. two or more growth centers occur in long bones |
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Term
| What roles does cartilage play in bone formation? |
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Definition
1. forms a temporary skeleton
2. provides growth plate |
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Term
| Mesenchymal cells form which cells that proliferate in cartilage? bone? |
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Definition
cartilage - chondroblast and chondrocyte
bone - osteoprogenitor cells |
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Term
| osteoprogenitor cells - where are they found? |
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Definition
found in periosteum, endosteum, and bone marroe
- bipotential stem cells to make fat or chondroblasts as well as bone
- made throughout life to make bones |
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Term
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Definition
| secrete macromolecular organic components of bone (GAG's etc.) |
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Term
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Definition
| transformed osteoblasts - respond to mechanical signals - mature cells |
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Term
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Definition
| multinucleated cells which resorb bone and are made from monocytes |
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Term
| what is the distance after which osteonal bone is required? |
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Definition
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Term
| Describe immature (primary) bone. |
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Definition
| cancellous (spongy) with trabeculae, reticular with no lamina, unorganized collagen, many cells and irregular staining |
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Term
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Definition
| cancellous or compact with osteons, lamellar, layered and polar collagen, few cells, and even staining |
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Term
| what is the difference between intramembranous and endochondral bone formation? |
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Definition
| intramembranous - bone forms in CT and is NOT preceded by cartilage |
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Term
| what is the prerequisite for ALL bone formation? |
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Definition
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Term
| Osteoblasts secrete what? |
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Definition
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Term
| What constitutes osteoid? (4) non-mineralized bone |
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Definition
1. collagen type I = 90% of organic content for strength
2. proteoglycans
3. non-collagenous proteins
4. glycoproteins |
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Term
| what triggers mineralization? |
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Definition
1. alkaline phosphatase which hydrolyzes inhibitors like pyrophosphate
2. Ca[P} product increases so calcium phosphate deposits in solid phase
3. presence of nucleation sites such as collagen I and vesicles |
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Term
| mineralization occurs with ______ and ____ is deposited on ____ and ____ |
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Definition
extracellular deposition of hydroxyapatite forming crystals to make the major INORGANIC component of bone
= hydroxyapatite is deposited on collagen I and matrix vesicles (secreted by osteoblasts) |
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Term
| What is the formula for hydroxyapatite crystals? |
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Definition
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Term
| What are three things that facilitate mineralization? |
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Definition
1. osteonectin
2. growth factors, especially TGF-Beta
3. hormones like calcitonin, estrogen, and androgens |
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Term
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Definition
| glycoprotein that binds Ca and collagen I and mediates deposition of hydroxyapatite onto collagen fibers - like chondronectin in cartilage |
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Term
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Definition
| key inducer of collagen and stimulator of alkaline phosphatase production and other bone matrix components (growth factor) |
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Term
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Definition
| inhibits osteoclast resorption and increases mineralization |
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Term
| estrogens and androgens ____ mineralization; PTH ___ osteoclasts and ____ mineralization |
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Definition
increase
- increases
- decreases |
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Term
| Why is bone resorption necessary? |
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Definition
1. bone grwoth is appositional so resorption shapes the bone to minimize bone mass
2. bone is a storage site and minerals are resorbed and replaced when needed |
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Term
| What are the key regulators of resorption? |
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Definition
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Term
| What do osteoclasts do? where are they found? |
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Definition
function: secrete organic acids to decalcify bone and secrete hydrolytic enzymes to digest organic matrix
found in the absorption cavity (Howships lacuna) |
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Term
| What stimulates osteoclasts? |
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Definition
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Term
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Definition
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Term
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Definition
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Term
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Definition
| needle like calcification of bone that later becomes trabeculae |
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Term
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Definition
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Term
| When does intramembranous ossification begin? |
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Definition
| 9 weeks into fetal period or end of second month of gestation |
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Term
| Where is intramembranous ossification found? |
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Definition
| in many flat bones and in membranes formed by mesenchyme; NOT preceded by cartilage |
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Term
| What is the order of intramembranous ossification? |
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Definition
1. capillaries grow into bone tissue and the surrounding mesenchymal cells become osteogenic and differentiate into osteoblasts
2. matrix is secreted
3. matrix calcifies and osteoblasts become osteocytes to form canaliculi
4. spicules form and enlarge into trabeculae
5. immature bone is replaced by mature lamellar bone
6. 2 plates of bone/tables develop on the periphery
7. tables are separated by diploe |
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Term
| Where is endochondral ossification? |
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Definition
| long bones and irregular bones |
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Term
| what is the cartilage model? |
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Definition
| precedes ossification as a temporary skeleton growing interstitially and appositionally with chondrocytes and chondroblasts |
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Term
| When does endochondral ossification begin? |
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Definition
| end of second month of gestation |
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Term
| Describe steps of endochondral ossification |
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Definition
1. growth first starts at perichondrium when capillaries penetrate, the innter cells begome osteoblass and ossification begins
2. bone collar develops
3. capillaries invade at midpoint of shaft and chondrocytes hypertrophy
4. cartilage calcifies and disintegrates to form primary center of ossification - diaphysis
5. bone grows in length and width and resoprtion also ccurs on the endosteal surface
6. secondary centers of ossification with vascular invasion - epiphysis
7. primary and secondary centers separated by growth plate and cartilage proliferates |
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Term
| What are the zones of cartilage cells in the epiphyseal plate? |
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Definition
1. resting/reserve cartilage
2. proliferating
3. hypertrophying
4. degenerating |
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Term
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Definition
| region where ossification is occuring as cartilage erodes (includes entire spongy area beneath growth plate) |
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Term
| What accelerates the fusion of the epiphysis and metaphysis? |
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Definition
| testosterone and estrogen |
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Term
| Where does bone deposition occur? (3) |
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Definition
1. periphery of bony epiphysis
2. metaphysis
3. under periosteum in diaphysis |
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Term
| where does bone resorption occur? (3) |
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Definition
1. internal (endosteal) part of diaphysis
2. metaphysis at junction of diaphysis
3. under periosteum at distal part of metaphysis |
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Term
| When does ossification occur during the embryonic period? |
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Definition
membranous - centers evident at 9 weeks
endochondral - centers evident at 8 weeks
- starts in clavicle, mandible, and arms |
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Term
| Where does ossification occur during the fetal period? |
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Definition
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Term
| What bony development occurs in childhood? |
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Definition
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Term
| What bony development occurs in adolescence? |
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Definition
| other epiphyses and some fusion of primary and secondary ossification centers |
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Term
| what bony development occurs in young adults (ages 20-22) |
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Definition
| complete fusion of all bones |
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Term
1. parietal and frontal bones develop by which forms of ossification?
2. long bones
3. temporal and occipital bones? |
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Definition
1. membranous
2. endochondral
3. mixed |
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Term
Rickets (kids) and osteomalacia and late rickets (adults)
- causes |
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Definition
due to vit D deficiency or poor absorption or metabolism
congenital - impaired phosphate metabolism or phosphate deficiency
**POOR MINERALIZATION - organic components are normal |
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Term
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Definition
poor calcification
- skeletal deformities such as bowed legs due to excess osteoid |
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Term
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Definition
Vitamin C deficiency
- insufficient organic compoentn |
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Term
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Definition
decreased collagen, thin bones, weak bones
POOR PREBONE FORMATION
- |
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Term
Dwarfism
- 2 types
- causes |
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Definition
1. pituitary - inadequate growth hormone and too few chondrocytes
2. achondroplasia - failure of normal endochondral bone formation (hereditary)
- problem with cartilage growth plate
- most common form of dwarfism |
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Term
| What are the steps of bone fracture repair? (5) |
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Definition
1. clot formation
2. periosteal, endosteal and marrow cells proliferate
3. cartilage is laid down
4. callus formation and primary immature bone is formed
5. mature bone formed in remodeling |
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