Bone Flashcards
Function of bone
support/protect, produce RBCs, facilitation of movement, storage of minerals
Three structural components of bone
Diaphysis, Metaphysis and Epiphysis
where is spongy bone located
epiphysis
where is red bone marrow
the spongy bone
where is yellow bone marrow
the diaphysis or the shaft of the bone
Composition of bone
Extracellular matrix and cells
Bone cells
fibroblasts, osteoblasts, osteocytes, osteoclasts, osteogenic
fibroblasts
produce collagen and other components of the ECM
osteoblasts
form new bone, synthesize and secrete the collagen matrix and calcium salts
located in the epiphyseal plate, endosteum and periosteum
osteocytes
lo longer forming bone cells there just maintain the mineral concentration, these are entrapped in the matrix
osteoclasts
actually “eat” the osteocytes, to reabsorb bone
are found on bone surfaces and at injury sites
Osteogenic Cells
differentiate into osteoblasts
located in the deep periosteum and the bone marrow
types of bone
cortical and cancellous
what are the thin plates in the spongy bone
what is the function of them?
trabeculae; to distribute contact stresses and absorb dynamic loads
the arrangement of them show how the stress is applied
What does it mean that trabeculae is anistropic?
the bone withstands force in different directions but not all the same amount. The bone will be stronger in some directions than others
periosteum
outer fibrous layer
contains nerves, blood vessels and lymph, encases the endosteum so tendons and ligaments attach here, thinner
endosteum
contains the central canals and surrounds the bone marrow
Woven bone
collagen fibers are irregularly arranged to form a pattern of alternating coarse and fine fibers
FOUND IN NEWBORNS OR CALLUSES
Lamellar Bone
mature bone; makes up most of the adult skeleton
Osteogenic layer
the innermost layer
contains fibroblasts, stem cells and osteoblasts
decreased healing here
sharpeys fibers connect to the deeper layers of bone
Compact bone and blood supply
vessels run up/down through the Haversian canals or central canals
Cancellous bone and blood flow
blood vessels in the periosteum and blood in the marrow cavities
has very good blood supply
Types of loads that occur on bone
tension, compression, shear, torsion and combined loading
what type of force is bone the most capable of resisting
compression
Wolff’s Law
Bone remodels in response to external stresses, weight bearing and muscular tension
Cortical bone is ____ than cancellous bone (looser or stiffer)
stiffer
cortical bone can withstand more ___ than cancellous bone but less ____ than cancellous bone
stress, strain
before failing, cancellous bone can sustain ____ % strain
75% strain
Cancellous bone stress and strain
LOW STRESS HIGH STRAIN
Cortical bone stress and strain
HIGH STRESS LOW STRAIN
fails if strain is >2%
High loads over a short time will produce
high stress, low stiffness and greater load before fracture
low loads over long periods of time will produce
not as stiff or strong, fractures under lower loads, HIGH STRAIN
What happens when bone is immobilized
the bone is reabsorbed but not produced
there is decreased collagen synthesis and mineral content (regional osteopenia)
and weakened connections of tendons and ligaments
cancellous bone healing
there is little or no callus formation
healing occurs through direct osteoblastic activity
Cortical bone healing steps
- inflammation
- soft callus (blood clot replaced by fibrous tissue/cartilage)
- hard callus (woven bone deposited on both sides of fracture site, eventually forms a collar around the bone)
- remodeling of bone until it is lamellar
Aging effects
bone density starts to decline at the age of 30
post-menopausal at risk for osteoporosis due to loss of estrogen
bone stiffness decreases and has a decreased load to failure
effect of repeated loading
can cause permanent strain and bone failure due to less stiffness, more deformation and a lower load to failure
