Bone Flashcards
What is happening in the bone during disuse?
osteoblast number and activity is decreased, osteoclasts remain unchanged
bone is continuously resorbs but new bone is not laid down as normal
Ca2+ release from bones is an indication of what?
bone is being resorbed and calcium is being liberated from the bones
How does parathyroid hormone (PTH) respond to calcium levels in the blood?
PTH levels fall when calcium levels are high (i.e. during immobilisation), they rise when calcium levels fall (i.e. during mobilisation)
Why is a rest period between loading important for the modelling of bone?
Cells that signal loading in bone become desensitized after a period of repeated loading. Rest allows them to recover their sensitivity and thus signal loading and induce bone formation again.
When do females gain the most bone?
pre-menstration
Why are females are greater risk of fractures due to falls later in life?
females typically have lower bone mineral density post-menopause
what is bone safety factor?
maximum force the bone can withstand/the force bone needs to withstand everyday life
bones have a capacity just higher than what they need for everyday activities to withstand rupture.
How does bone fail during fatigue loading?
the bone is loaded and unloaded repeatedly within its elastic region. Over time the bone looses stiffness and retains deformation after unloading. Finally, the bone fails because of the accumulated microdamage.
What structures stop bone fracture propogation?
central canals, volkmann’s canals, lacunae, cement lines and the way bone is formed into lamellae within the osteons, the arrangement of collagen fibrils
How is trabecular bone weakened over time?
the loss of struts- while a small fracture in a strut can be repaired through remodelling, a complete break through a strut cannot be repaired and that strut is no longer contributing to structural support during compressive loading
What is the difference between cortical and cancellous bone?
- arrangement: cortical bone is arranged in a single direction whereas cancellous is arranged multi-directionally
- functions: cortical bone functions as a lever whereas cancellous bone functions as a shock absorber
- cortical bone has a higher elastic modulus (stiffer), cancellous bone has a lower elastic modulus (more compliant- can deform 50% of its original length before deformation)
Why do we need both modelling and remodelling of bone?
remodelling is a continuous process throughout lifetime to maintain bone, modelling is due to mechanotransduction and allows bones to become better suited for loading
How would changing the polar moment of inertia affect a bones loading capacity?
a larger polar moment of inertia (larger diameter/thinner cortex) increases a bones ability to absorb compressive forces
