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31 Cards in this Set
- Front
- Back
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2 processes by which mesenchymal cells form bone |
intramembranous ossification endochondral ossification |
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process by which direct bone formation of mesenchyme occurs |
intramembranous ossification |
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what bones undergo intramembranous ossification? |
cranial vault some facial bones parts of mandible and clavicle |
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describe the process of intramembranous ossification |
1. mesenchyme condenses to form bone blastema; this mass of cells differentiate into osteoblasts and they bury themselves into the bone matrix (osteoid), but osteocytes are not mineralized yet. 3. woven bone (primary bone tissue) is developed, but osteoclasts resorb it and the bone gets replaced by lamellar bone |
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the skeletal structures in which endochondral ossification occurs |
axial skeleton (excluding cranial vault) some facial bones appendicular skeleton
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describe the steps of endochondral ossification |
1. mesenchyme express SOX 9 to differentiate into chondroblasts, laying down a cartilage layer ( hyaline cartilage will serve as template for the long bone) 2. the perichondrium (cartilage producing layer) @ the diaphysis will transform into periosteum, which will lay down bone around cartilagenous model 3. the primary ossification center forms as a result chondrocyte differentiation |
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endochondral ossification is a predetermined program of what type of cell differentiation? how? |
chondrocyte differentiation.
chondrocyte proliferation @ diaphysis initiates the formation of the PRIMARY OSSIFICATION CENTER. The cells hypertrophy, secreting vascular endothelial cell growth factor to elicit BV from perichondrium. Then cartilage begins to calcify/mineralize. Then hypertrophic chondrocytes undergo apoptosis |
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after endochondral ossification, what anatomical region of the bone is cartilage restricted to? |
epiphyses--at the articular surface |
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where is the primary ossification center located on the bone and what anatomical direction does extend? |
It's in the middle of the bone shaft and it extends proximally and distally from the center
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where is the secondary ossification center located in bone and in what direction does it extend? |
at the epiphyseal ends; radially |
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how long is cartilage retained @ the growth plate? |
puberty |
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how is the secondary ossification center established? |
BV and mesenchyme infiltrate the epiphysis |
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from the direction of the growth plate to the diaphysis, name the different zones of the growth plate |
1. resting zone (reserve) 2. proliferative zone 3. pre-hypertrophic maturation zone 4. hypertrophic zone 5. calcification/vascular invasion |
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describe the appearance and function of resting zone below the growth plate on bone |
????????? |
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describe the appearance and function of a bone's proliferative zone |
cells (chondrocytes) sit in columns and discoid shaped
where chondrocytes expand and proliferate; this interstitial growth increases the length of the cartilage |
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describe the appearance and function of a bone's pre-hypertrophic maturation zone |
chondrocytes sit in columns and discoid shaped, but larger than cells in proliferative zone
where chondrocytes start to enlarge |
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describe the appearance and function of a bone's hypertrophic zone |
cells are large and the cartilage matrix b/w cells are attenuated
these chondrocytes send out signals to vasculature below (closer to diaphysis); cartilage matrix around hypertrophic cells begin to calcify |
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describe the appearance and function of a bone's calcification/vascular invasion zone |
the matrix is mineralized, this zone is closest to bone shaft's center
this region receives signals from hypertrophic chondrocytes to mineralize the cartilage matrix above it. Osteoclasts start chewing at transverse septae of calcified cartilage, leaving longitudinal septae as framework for osteoblasts to place woven bone. The osteoblasts resorb woven bone for lamellar bone to replace it
this area enlarges the bone marrow cavity
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which cell types "run" and "chase" during bone growth in length? |
osteoclasts "chase" chondrocytes "run" |
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what tissue layer functions as a surface growth plate (epiphyseal growth plate) during postnatal development?
What is it's purpose? |
articular cartilage layer around secondary ossification center: expands the region of epiphysis by providing chondrocytes for both lateral and vertical growth |
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Which bone formation process contributes to long bone growth in length? and long bone growth in diameter? |
endochondral ossification: length intramembranous ossification: diameter |
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at what life stage is bone modeling more common in? |
immature bone |
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describe the process of bone MODELING |
osteoclasts and osteoblasts work INDEPENDENTLY of each other to remove bone @ some sites and add bones @ other sites to alter bone shape and size |
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what 4 hormones are important for growth plate regulation?
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1. growth hormone (GH) 2. IGF-1 (insulin like growth factor) 3. thyroid hormone 4. estrogen
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what is the function of growth hormone in bone growth? |
GH regulates bone growth in length:
GH (secreted by anterior pituitary) stimulates IGF1 secretion from liver and recruits chondrocytes into the proliferation zone of the growth plate and stimulates the cells to synthesize IGF, which will stimulate chondrocyte proliferation and hypertrophy in growth plate |
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what is the function of IGF-1 in bone growth? |
IGF-1 regulates bone growth in length:
IGF-1 stimulates chondrocyte proliferation and hypertrophy in growth plate |
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what is the function of thyroid hormone in bone growth? |
TH regulates bone growth in length:
thyroid hormone promotes GH synthesis and promote chondrocyte hypertrophy |
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what is the function of estrogen in bone growth? |
it's critical for normal bone growth and growth plate fusion (both sexes)
they promote proliferation in growth plate they promote growth plate senescence as proliferative capacity of cells is exhausted |
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how does a pituitary tumor affect bone growth? |
pituitary tumor would produce excess GH before puberty, thus causing gigantism |
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how does hypothyroidism affect bone growth? |
it slows longitudinal bone growth and endochondral ossification b/c Thyroid hormone is insufficient in causing chondrocyte hypertrophy which contributes to lengthening of bone |
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(from lec 11/12)
what are the differences b/w intramembranous ossification and endochondral ossification? |
1. I.O. has only 1 ossification center, E.O has multiple 2. I.O-bone directly formed from mesenchyme; E.O. bone formed from pre-formed cartilage model
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