Bone Flashcards
2 aspects of bone ECM
- mineral
2. Organic
Features of bone mineral
- 70% of wet weight
- provides rigidity and mineral storage
- Calcium and phosphorous
Features of bone organic
- osteoid
- 30% of wet weight
- provides resilence
Content of osteoid
- 90-95% is type 1 collagen
- glycoproteins
- proteoglycans
3 types of bone cells
- Osteoblasts
- Osteoclasts
- Osteocytes
Features of osteoblasts
- from progentor cells
- at surface of bone matrix
- produce and calcify osteoid
Gene resp. for osteoblast dev.
CBFA1
Features of osteocytes
- from osteoblast that were surrounded - in lacuna
- connected via canaliculli
- maintains bone matrix
Features of osteoclasts
- from bone marrow
- multinucleated
- breaks down bone
depressions for osteoclasts
howships lacunae
Wolf’s law
Bone - use it or lose it
Mech. of Ca increase
If Ca down > PTH up > osteoctyes osteolysis
AND > PTH up > osteoblast upreg CSF > more clast number and activity
2 types of bone
- spongy (cancellous)
2. compact
Feat. of spongy bone
- crossbridging of spicules adds strength
- org. of spicules reflects stress direction
- bone marrow filles spicules
locations of spongy bone
irregularly shaped bones and epiphyses of long bones
feat. of compact bone
- forms bone periphery
- osteocytes array in Haversian systems
location of haversian systems (osteon)
- parallel to axis of long bones
contentsof haversian canals (5)
- vessels
- nerves
- osteoblasts
- conn. tissue
- progenitor cells
what lies between rings of osteocytes
lamellae - adds to strength
function of multidirectional collagen fibers in osteo
resists torque forces
locations of woven bone
sites of rapid decomp. - breaks, young bones
feat. of woven bone
not in osteons - more random configuration
6 basic parts of bone
- periphery - compact bone
- diaphysis - the shaft - think compact bone collar with fat inside
- metaphysis - wide part of shaft, begins to be filled with red marrow
- epiphysis - the end - compact bone out with spongy inside
- periosteum - dense irregular tissue on ext. surface
- endosteum - thin layer of CT lining marrow cavity
Path of intramembranous ossification
prog. cells>CBFA1>osteoblast>secrete matrix>osteocyte>spicules enlarge>compact bone>some vessels trapped> haversian canals
main feature of endochondrial ossification
begins with hyaline cartiledge which is replaced
steps of endochondrial ossification
- chondrocytes at center hypertrophy>calcification
- osteoblast dev. from prog. cells>bone collar
- chondrocytes secrete VEGF>penetration of vessels
- osteoclastic breakdown of cart.
- prog. cells in CT accompany vessels>osteoblasts
- vessels branch toward end cart.
- process repeats at 2ndry centers
- tips of spicule trimmed by clasts to open up diaphysis
- spicules at end of bone remain, but will be turned to bone
how bones grow width
- intramembranous ossification
- blasts diff. on outside to make new collar
- clasts work on inside to thin collar
how bones grow length
- At epiphyseal cart. / growth plate
- cart. grows interstitially and replaced by bone
5 zones of epiphyseal plate
- zone of reserve - quiet chondrocytes attaching plate to bone
- zone of proliferation - rapid prolif. @ right angle to length of bone
- zone of hypertrophy - chondrocytes enlarge and begin to lay down matrix between them
- zone of calcification - marix begin to calcify and chondrocytes apop.
- zone of ossification - blood vessel penetrate on diaphyseal side
