Compare compact bone to trabecular
compact has haversian system with osteons and circumfirential lamellae
trabecular: has spicuateled
•80-90% of volume is calcified
•Fulfills mainly a mechanical and protective function
•15-25% of volume is calcified
•Fulfills mainly a metabolic function •~20% of bone
Cortical and trabecular bone are constituted of the same cells and the same matrix elements, but there are ______ differences.
structural and functional
Where does most of the bone breakdown happen? whats the timeline for this process?
in trabecular bone
2 weeks to breakdown, months to rebuild
Explain process of bone remodeling
Have osteoclasts lead teh way followed by blasts laying out new bone behind them
12 BRUs activated each minute, with annual turnover rate of 25%. l High turnover rate because of
the higher surface-tovolume ratio; accounts for 80% of turnover
3 BRUs activated each minute, with annual turnover rate of 2-3%.
l Lower turnover rate; accounts for 20% of turnover
l Less vascularity
Osteoid laid down in discrete layers, 3µm thick
l Lamellae deposited in curved sheets that follow the contour of the trabeculae
buidling of trabecular bone
Osteoblasts plus blood vessels follow osteoclasts through hollowed-out tunnel
l Concentric lamellae laid down
Cortical bone growth
what is the heirarchical structure in bone?
collagen moleculre (type I) --> collagen fibril--> fibers--> lacuna--> haversian canal
the heirarchical structure of bones supplies them with what characteristics?
stiff, strong, tough and ductilie
resist damage, can be bent but also resist it and can bend before it bbreaks
What is the role of cement lines in bone?
both parallel and perpendicular
the perpendicular are better at resisting fracture
Why do we say that bone has dual physiology?
• Mechanical physiology – Loading – Unloading
• Mineral balance physiology – Ca balance – Phosphate balance
A skeletal disorder characterized by
– Compromised bone strength predisposing to
– An increased risk of fracture
WHO Definition of Osteoporosis
Bone strength reflects the integration of two main features:
– Bone density (easily measured)
– Bone quality (not as easily measured with presently available tools)
Long bones are slightly curved and are loaded primarily by_____
• There is tension on 1 side of the bone and compression on the other
• Vertebrae are loaded primarily in ____and ____
compression and torsion
•Past vertebral deformity is_____ predictive of future vertebral fracture than a 1 SD change in spinal BMD
•Past vertebral deformity is_____ predictive of hip fracture as a 1 SD change in spinal BMD
•These risks are_____ of age and BMD
What can we see on histology of bone with osteomalacia?
see lots of osteoid and unmineralized shit
Medications to ts osteoporosis
The interfaces between lamellae, and between osteons are called ______ and can absorb and dissipate force while preventing a crack from passing from one lamella to its neighbor.
While osteoporosisis a recognized clinical diagnosis, conceptually it is problematic. People do not suffer from low bone mineral density (BMD) unless they suffer____. Whether fractures occur depends on many factors in addition to BMD. For these reasons, it is more correct to consider osteoporosis as a risk factor for fracture, j
dual energy X-ray absorptiometry (DXA).A T-score ___ in a postmenopausal woman or a man over 50 is defined by the World Health Organization as the densitometric criterion for osteoporosis
A key difference between osteomalacia and osteoporosis is that in the latter, the quantity of _____is insufficient and its architecture is impaired
In adults, osteod volume is normally under 5% of the bone surface, but in osteomalacia, the osteoid surface is increased, sometimes dramatically so. PTH is typically elevated, as mineral deficiency drives
The bone isoform of ______ (tissue non-specific alkaline phosphatase, encoded by the TNSALP gene) and_____ (N-terminal propeptide of type 1 collagen) are typically elevated, as osteoblasts are working properly and secrete all their usual products.
Antiresorptives work by limiting the initiation of new bone remodeling units to tx osteoporosis ,why does this work?
Since bone formation takes longer than bone resorption, inhibiting the process of remodeling at its inception allows the remodeling space to be filled.
For simple nutritional deficiency leading to osteomalacia, what can we do to tx pts?
improving diet or giving supplements to provide sufficient vitamin D and Ca is sufficient therapy.
It is important to note that the elemental Ca content of supplements varies, based on the molecular weight of the anion.
CaCO3 is___% elemental Ca
while Ca citrate is only___% elemental Ca.
tamoxifen, raloxifene are both examples of
Estrogens and Selective Estrogen Receptor Modulators (SERMs, e.g.
h estrogens and SERMs can prevent the increased remodeling