Term
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Definition
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Term
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Definition
| another term for the formation of bone |
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Term
| what are the two methods of ossification? |
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Definition
intramembranous
endochondra |
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Term
| what is the result of intramembranous ossification? |
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Definition
| production of flat bones (of skull and most of clavicle) |
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Term
| what is the result of endochondral ossification? |
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Definition
| responsible for producing most of the skeleton |
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Term
| what does endochondral ossification create bone out of? |
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Definition
| bone develops from hyaline cartilage model |
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Term
| when does endochondral ossification occur? |
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Definition
| six weeks fetal development to early 20s |
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Term
| what are the first two steps for intramembranous ossification? |
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Definition
1. An area of the embryonic connective tissue (mesenchyme) condenses into a layer of soft tissue with a dense supply of blood capillaries. The mesenchymal cells enlarge and differentiate into osteogenic cells, and regions of mesenchyme become a network of soft sheets called trabeculae.
2. Osteogenic cells gather on these trabeculae and differentiate into osteoblasts. These cells deposit an organic matrix called osteoid tissue—soft collagenous tissue similar to bone except for a lack of minerals . As the trabeculae grow thicker, calcium phosphate is deposited in the matrix. Some osteoblasts become trapped in the matrix and are now osteocytes. Mesenchyme close to the surface of a trabecula remains uncalcified, but becomes denser and more fibrous, forming a periosteum. |
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Term
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Definition
| deposit soft osteoid tissue and then calcify it into bone |
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Term
| what do calicified trabeculae become? |
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Definition
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Term
| how is compact surface bone formed? |
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Definition
| filling in the spaces between trabeculae (forming spongy bone) with osseous tissue |
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Term
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Definition
| embryonic connective tissue |
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Term
| what are the last two steps of intramembranous bone development? |
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Definition
3. Osteoblasts continue to deposit minerals, producing a honeycomb of bony trabeculae. Some trabeculae persist as permanent spongy bone, while osteoclasts resorb and remodel others to form a marrow cavity in the middle of the bone.
4. Trabeculae at the surface continue to calcify until the spaces between them are filled in, converting the spongy bone to compact bone. This process gives rise to the sandwichlike arrangement typical of mature flat bones. |
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Term
| how is the primary ossification center formed in endochondral ossification? |
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Definition
| formed by chondrocytes in the middle of the cartilage model that enlarge |
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Term
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Definition
| small space containing an osteocyte in bone or a chondrocyte in cartilage |
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Term
| how is marrow cavity formed in endochondral bone development? |
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Definition
| cartilage lacunae (the small spaces containing chondrocytes in cartilage) break down as the chondrocytes enlarge to form the primary ossification center |
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Term
| what happens to the chondrocytes as their lacunae break down to form the primary marrow cavity? |
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Definition
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Term
| how do stem cells enter the primary marrow cavity? what happens once they're there? |
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Definition
enter via blood vessels
differentiate into osteoblasts and osteoclasts |
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Term
| what do osteoclasts do in endochondral bone development? |
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Definition
| dissolve cartilage remnants and enlarge the marrow cavity, which grows toward the ends of the bone. |
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Term
| what is the secondary marrow cavity? when does it start to form? |
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Definition
| ossification proceeds from secondary ossification center that appears near birth in the middle of the epiphysis. This creates a secondary marrow cavity at ends of new bones and leaves a layer of articular cartilage over the end of th ebone |
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Term
| do primary and secondary marrow cavities ever connect? |
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Definition
| no, they remain separated by a cartilaginous epiphyseal plate |
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Term
| how do bones become longer? |
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Definition
| by interstitial growth of cartilage in a transitional zone |
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Term
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Definition
the transitional zone in interstitial cartilage growth
lies between the primary marrow cavity and the cartilage of an epiphysis or epiphyseal plate |
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Term
| what are the five zones of the metaphysis in order of farthest to closest to marrow space? |
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Definition
1) zone of reserve cartilage
2) zone of cell proliferation
3) zone of cell hypertrophy
4) zone of calcification
5) zone of bone deposition |
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Term
| when are epiphyseal plates depleted/stop appearing completely? |
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Definition
depleted from the end of adolesence into the 20s
do not appear in adults 30 and older |
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Term
| what occurs in the zone of cell proliferation? |
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Definition
| chondrocytes multiply and form longitudinal columns of cells |
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Term
| what occurs in the zone of cell hypertrophy? |
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Definition
| chondrocytes in this zone enlarge |
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Term
| what occurs in the zone of calcifications? |
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Definition
| the matrix becomes temporarily calcified |
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Term
| what occurs in the zone of bone deposition? |
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Definition
| lacunae break down, chondrocytes die, and bone is deposited |
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Term
| what is the significance of epiphyseal plate depletion in late adolesence/early 20s? |
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Definition
| a bone cannot grow longer (a person cannot grow taller either) once the epiphyseal plates are depleted and the gaps between the epiphyses and the diaphyses close |
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Term
| what are epiphyseal lines? |
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Definition
| surface markings on bone where epiphyseal plates used to be before they undergo depletion in late adolescence/early 20s |
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Term
| what is appositional growth? |
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Definition
| growth of bone thickness and width; adds more matrix to the surface |
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Term
| to what other ossification process is appositional growth similar? |
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Definition
| appositional growth is similar to intramembranous ossification |
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Term
| what are the roles of calcium and phosphate in bone development? |
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Definition
| raw materials for calcified ground substance |
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Term
| what is the role of vitamin A in bone development? |
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Definition
| promotes formation of glycosaminoglycans (protein-carb fibers) |
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Term
| what is the role of vitamin C in bone development? |
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Definition
| promotes collagen cross linking |
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Term
| what is the role of vitamin D in bone development? |
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Definition
| necessary for calcium absorption by small intestine and reduces urinary calcium loss |
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Term
| what hormones stimulate bone growth? |
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Definition
calcitonin
growth hormone
estrogen
testosterone
thyroid hormone
insulin |
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Term
what does calcitonin do?
where does it come from?
who does it primarily affect? |
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Definition
a hormone secreted by the thyroid gland
stimulates osteoblast activity
functions chiefly in children and pregnant women
little significance in nonpregnant adults |
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Term
| how does growth hormone contribute to bone development? |
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Definition
promotes intestinal absorption of calcium
proliferation of cartilage at the epiphyseal plates
elongation of bones |
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Term
| how do sex steroids (estrogen and testosterone) contribute to bone development? |
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Definition
stimulate osteoblasts
promote growth of long bones, esp. in adolesence |
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Term
| what factors promote bone deposition? |
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Definition
thyroid hormone
insulin
local growth factors
parathyroid hormone (main player) |
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Term
| where are local growth factors produced? |
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Definition
| from within the bone itself |
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Term
| what stimulates the four small parathyroid glands to secrete PTH? Why? |
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Definition
Secrete PTH in response to a drop in blood calcium level
PTH stimulates osteoblasts which then secrete an osteoclast-stimulating factor that promotes bone resorption by the osteoclasts, thus maintains an appropriate blood calcium level
also reduces urinary calcium loss
promotes calcitrol synthesis |
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Term
| what is anchondroplastic dwarfism a result of? |
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Definition
| a spontaneous mutation that can arise any time DNA is replicated (dominant mutant allele) |
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Term
| do bones change throughout lifetime? |
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Definition
| yes, they are remodeled to accommodate bodily growth and changes in force applied to the skeleton |
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Term
| what is Wolff's law of bone? |
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Definition
| osteoblasts and osteoclasts reshape bones throughout life to adapt to the stresses placed on them |
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Term
| how does bone repair a fracture? |
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Definition
callus formation at the fracture site is composed of clotted blood. it eventually is replaced by connective tissue and cartilage
endochondral ossification follows |
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Term
| how long does it take for endochondral ossification to replace the cartilaginous plug of a fracture? |
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Definition
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Term
| which method of bone formation is referred to as being direct and why? |
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Definition
| intramembranous ossification- because there is no cartilaginous template as in endochondral ossification |
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Term
| which method of bone formation is referred to as being indirect and why? |
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Definition
| endochondral ossification- because a cartilaginous template is formed prior to ossification |
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Term
| Explain the sequence of intramembranous bone formation? |
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Definition
1. mesenchymal cells condense into a connective tissue membrane
2. mesenchymal cells differentiate into osteoblasts, osteoid is secreted and forms bone spicules
3. calcium phosphate salts are incorporated into osteoid matrix, osteoblasts are surrounded and become osteocytes
4. spicules continue to develop, the spaces inbetween form the marrow cavity, the outer and inner membranes undergo compaction
5. remodelling |
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Term
| What types of bones are normally formed by intramemrabous formation? |
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Definition
| flatbones, ie. of the skull |
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Term
| what is meant by endochondral ossification? |
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Definition
| bones are formed by a cartilage model |
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Term
| where does endochondral ossification initially occur? |
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Definition
| in the primary ossification center |
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Term
| which type of bone normally exhibits endochondral ossification? |
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Definition
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Term
| what is the first step in endochondral ossification? |
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Definition
| a fetal template of hyaline cartilage is formed |
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Term
| why is the first step in endochondral ossification important? |
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Definition
| must have template of cartilage for ossification to occur, the template is a model for what is to come |
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Term
| what is the critical second step in endochondral ossification? |
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Definition
| calcification of the perichondrium |
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Term
| where is the primary center of ossification located? |
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Definition
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Term
| what occurs at the primary center of ossification? |
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Definition
| osteoclasts resorb bone spicules to form marrow cavity, osteoblasts form new bone |
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Term
| how does the marrow cavity form in endochondral ossification? |
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Definition
| by the action of osteoclasts resorbing bone spicules |
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Term
| where do the secondary centers of ossification occur? |
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Definition
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Term
| what is the region dividing the primary and secondary centers of ossification called? |
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Definition
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Term
| what steps form the general process involved in growth of long bones? |
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Definition
| continued production of cartilage at the epiphyseal plate in the metaphysis region causes elongation - endochondral ossification |
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Term
| what type of bone growth is responsible for increase in width? |
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Definition
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Term
| what type of bone growth is responsible for increase in length? |
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Definition
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Term
| why do long bones stop growing in length? |
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Definition
| hormonal control of cartilage production at the epiphyseal plate stops |
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Term
| how does the stopping of long bones growing in length occur? |
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Definition
| the epiphyseal plate stops producing new cartilage cells, the ossification front from the primary ossification center ossifies the plate which is then resorbed by osteoclasts |
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Term
| what is formed as a result of the stoppage of long bones growing in length? |
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Definition
| a confluent marrow cavity |
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Term
| how is the stoppage of long bones growing in length controlled? |
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Definition
| hormones: gonadal and growth |
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Term
| what is involved in the healing of bone fractures? |
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Definition
| callus formation: clotted blood replaced by connective tissue, then endochondral ossification |
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