Ageing skeleton Flashcards
what does osteoprotegerin bind to
irreversibly binds to free RANK-L, preventing it from binding to osteoclast precursors and therefore inhibiting bone resorption
what is RANK-L released by and what is the function
osteoblasts and osteocytes, this binds to RANK on the surface of osteoclast precursors which causes them to form osteoclasts which migrate and bind to the bone surface to begin bone resorption
what is bone-remodelling
removal of small increments of bone and replacement with new
cyclical process, constantly resorbs bone in response to local or systemic triggers
most bone exists in a state of quiescence
what is bone remodelling done in response to
removal of micro-damaged bone
healing macro-damaged bone
response to changing loads
storage and release of calcium
how is bone remodelled
osteoclasts migrate to the site of activation, resorb bone then undergo apoptosis
osteoblasts on the bone surface the lay down new osteoid which is later mineralised to form solid bone, restarting the cycle
what does bone resorption allow for
calcium hydroxyapatite crystal breakdown and release of ionic calcium into the systemic circulation, opposite occurs when osteoid is mineralised
what does PTH do
triggers an increase in RANK-L secretion, and therefore more bone resorption and increased serum calcium levels
what is the action of calcitonin
produced by thyroid
has direct inhibitory effect on osteoclast activity resulting in less bone resorption, less calcium release and a lower serum calcium
when does peak bone mass occur
mid-20s
on average men have a higher PBM than women
after about 40yrs bone mass starts to gradually decline in both sexes
what happens to bone mass during menopause
during menopause circulating oestrogen levels decrease significantly, causing the protective effect to be lost and a rapid decrease in bone mass
what occurs after menopause
rate of decline of bone mass slows, slwoer than the average rate of decline of an average male, but due to the period of rapid decline the average bone mass of a female may drop below the fracture threshold
what is the fracture threshold
rough upper limit of bone density before osteoporotic insufficiency fractures occur
(fractures that occur with normal or low-energy forces)
what is the action of oestrogen on osteoblasts
act directly on them to limit the amount of RANK-L they release
means rate of resorption is similar to formation and bone mass is preserved
during menopause this inhibitory action is lost and osteoblasts secrete increased amounts of RANK-l, recruiting more osteoclasts and creating an imbalance in formation and resorption
what is osteoporosis
structure of bone is the same but there is much less of it
