module 9 bone formation Flashcards
axial skeleton
80 bones
skull
vertebral column
thorax
appendicular skeleton
126 bones
upper and lower extremities
shoulder girdle
pelvic girdle
bone cells
osteoblast
osteocyst
osteoclast
osteoblast
derived form mesenchymal cells produce type 1 collagen responde to parathyroid hormone produce osteocalcin synthesize osteoid (nonminderalized bone matrix)
osteocyte
transformed osteoblast surrounded in osteoid as it hardens from deposited minerals
- maintain bone
- help regulate Ca and Phos.
- stimulated by calcitonin
- inhibited by PTH
osteoclast
from hematopoetic tissue (monocyte/macrophage lineage)
major reabsorptive cell of the bone
large, multinucleated cells
contain lysosomes filled with hydrolytic enzymes
bone maxtrix
organic part: 25% - collagen - proteoglycans - glycoprotines inorganic part: 65% - calcium - phosphate -- crystals of these minerals called hydroxyapatite
osteoid
organic matrix
- collagen fibers extend along parallel lines of tension: give bone tinsel strength and some flexibility.
proteoglycan
part of osteoid
polysaccaride that binds between collagen fibers and surrounds cells.
may transfer mechanical info within matrix
Inorganic matrix
mineral content bound and embedded in in matrix gives bone hard, rigid structural strength reservoir for the body calcium and phosphorus
basic unit of bone
osteon or the harersian system
haversian canal
blood vessels and nerve fibers run through this
-surrounded by mineralized matrix: lamellae
lucunae
small cavities bordering the lamellae that contain a bone cell, osteocyte.
canaliculi
small channels that connect adjacent lamellae, allows nutrients to move through
2 bone types
cancellous/trabecular/spongy
compact/cortical
cancellous/spongy bone
network of thin plates and rods: trabeculae
- found within ends of long bones, vertebral bodies, flat bones (pelvis)
- trabeculae laid in response to stress and shaped to accommodate loads placed on bone
- enclosed in shell of compact bone
compact/cortical bone
resistant to compression
dense in structure
laid in concentric layers
periosteum
tough fibrous memrane that covers all bone
- highly vascularized
- provides nutrition via volkmann canals
- inner layer contains osteoblasts
- covers entire bone except for the ends which are covered by hyaline (articular) cartilage
long bones
medullary cavity: central cavity is present
- endosteum: thin membrane that lines inside of cavitiy
- – contains osteogenic cells
- in children: filled with red marrow
- in adults: largely yellow marrow
- – red marrow primarily in flat bones of adults
endochondral ossification
longitudinal bone growth, evident in embryonic development, fracture healing, some bone tumor growth.
- mesenchymal cells differentiate into chondrocytes which produce a carilaginous “model” of bone
- mineralized starting at center (primary assification)
endochondral secondary ossification
centers form near ends of long bones ( epiphyses)
- future site of bone growth into teen years.
intramembranous ossification
flat bones grow by circumferential growth process
- vascularized fibrous tissue becomes mineralized as the mesenchymal cells present differentiate into osteoblasts.
continuous bone growth
bones increase in length only through growth within cartilage plate followed by endochondral ossification
epiphyseal plate
allows for lengthening of diaphysis and metaphysis
- site of continuous growth
growth and thickening of cartilage cells of the plate move the epiphysis away from the metaphysis
- calcification and replacement of cartilage occur on metaphyseal surface
metaphysis
between diaphysis and epiphysis
zones of epiphyseal plate
calcifying cartilage
maturing cartilage
proliferating cartilage
resting cartilage
calcifying cartilage zone
thin line of condrocytes
weakest part of plate
condrocytes no longer active due to calification of matrix
resting cartilage zone
maintain adherence of plate to epiphysis
proliferating cartilage zone
young
demonstrates most active cell growth
maturing cartilage zone
contains enlarged and mature cartilage cells as they migrate towards the metaphysis
osteoblast within periosteium
responsible for growth in width of bones via intramembranous ossification
thyroxine hormone
decreased levels lead to dwarfism
GH
decreased levels lead to dwarfism
increased levels lead to giantism
estradiol hormone
during puberty causes more rapid maturation and fusion of plates
- can limit growth spurts of puberty, and early sexual maturity, especially in girls, leading to shorter stature
bone remodeling phases
1: activation phase
2: resorption phase
3: formation phase
activation phase of remodeling
osteoclasts are responsible for bone breakdown
- has receptor for RANK L that stimulate bone reabsorption
- stimulated by IL-10 and bisphosphonates
reabsorption phase of remodeling
osteoclasts form a cutting cone, resorb bone, and leave behind and elongated cavity
- compact bone: resorption cavity follows longitudinal axis
- spongy bone: resorption cavity parallels the surface of the trabeculae
formation phase of remodeling
new bone laid down by osteoblasts lining the walls of the resorption cavity
- successive layers laid down
- new trabeculae formed in spongy bone
RANKL
secreted by osteoblast
receptor on osteoclast
- when activated cutting and resorbing of bone continues
OPG
secreted by osteoblast
receptor antagonist for RANK receptor
deactivates osteoclast
RANKL expression
increased by - IL: 1, 11, 17 - PTH - prostaglandin - glucocorticoids decreased by - IL-4 - estradiol
OPG production
increased by - IL: 1, 13, 18 - estradiol - leptin - mechanical strain Decreased by - PTH - prostaglandin - glucocorticoids - cyclosporin
calcium homeostasis
- majority of Ca stored in bone
- blood concentration tightly controlled
- PTH maintains serum Ca levels by increasing bone reabsorption as well as Ca reabsorption in renal tubules
- Vit. D increases bone mineralization by increasing Ca absorption in GI tract
- in Ca defeciency can stimulate bone resorption to maintain blood concentration
calcitonin
inhibitor to bone resorption
5 stages of fracture healing
hematoma formation fibrocartilage formation callus formation ossification consolidation/remodeling
hematoma formation, fx healing
size depends on amount of damage
offers some stability to fractured ends
inflammation
fibrocartilage formation, fx healing
3 days- 2 weeks
granular tissue containing blood vessels, fibroblasts, osteoblasts
callus formation, fx healing
2-6 weeks
cartilaginous callus
formation of bone at periosteal surfaces to unite outer ends
if this stage is delayed or interrupted final stages do not occur
Ossification, fx healing
3-6 months
space in bone bridged and fractured ends united
callus slowly replaced by spongy bone
consolidation/remodeling, fx healing
6 weeks - 1 year
medullary canal established
bone resorbed and deposited along stress lines to meet mechanical requirements
