bone Flashcards
structure of a long bone
spongy- crossbridge, no blood vessels going through so nutrients can just diffuse through
compact bone- provides strength
trabecular- provides strength in different directions, found in epiphyses, consists of network of struts and plates, in contact with red bone marrow
bone constituents
mineral- 70%- mostly hydrooxyapatite
protein- 28%- largely type 1 collagen
cells - 2%
- osteoblasts- bone forming cells dervied from mesenchymal stem cells
- osteocytes- mature osteoblasts, miantenance
- osteoclasts- multinucleated bone reabsorbing cells, dervied from haemotopoietic cell line
bone remodelling
osteoclasts- dissolve old bone
osteoblasts- secrete osteoid + mature into osteocytes
osteoid mineralised to form new bone
osteoid consists of collagen and other proteins
bone remodelling- stem cells
MSCs- can differentiate into cells that can give rise into different cell types and tissues- eg chondrocytes, fibroblasts and adipocytes (depends which signalling molecules are present)
HSCs (hematopoietic)- derive into a range of different cells in blood including osteoclasts
cell signalling
RANKL and OPg are released by osteoblast
RANKL- stimulayes activity of osteovlast (when bone is old)
OPG- reduce acitvity of osteoclast (when new bone is being formed)
bone metab with age
factors contributing
- impaired formation- MSC differentiation- greater predispisition than osteoblast lineage in older vells- reduced GH/IGF1- reduces bone formation, oestrogen deficiency- contributes to reduced bone formation
- increased reabsorption- due to oestrogen deficiency (RANKL expression increased), greater osetoclast responsiveness to RANKL, calcium or vit D deficiency/hyperparathyroidism
changes in bone remodelling with age
young person- bone reabsorption= bone formation
post menopausal women have increased reabsorption
stress riser (stress fractuure)- if bone breaks it can lose the cross bridge, producing structural changes in bone
after menopause, resoprtion increases more than formation
changes in corticol bone remodelling
corticol- dense and solid, surrounds marrow bone
young peson- large osteons and little intersitial bone
older person- smaller osteons and more interstitial bone
with reduced cellular activity there are smaller osteons and more space between osteons (interstitial space) which isnt being replaced as rapidly
= more bone damage
bone mineral density
BMD (g/cm2)= mass of bone (g) per unit area (cm2)
BMD increases throughout life then decreases with age both at the hip and spine
larger decreases in hip BMD compared to spine
differences also due to genetics, race, diet, nutrition, environment etc
trabecular bone has more rapid reduction in BMD
changes in bone shape
bone area and outside diameter are increasing, bone gets wider as you get older
adaptation to cope with the reduced bone mass as it makes the bone harder to break
contributes to chnages in thickness of bone- bottom of the bone remains thick (where force is applied) but the top of the bone is a lot thinner due to bone loss- reducing overall bone strength
changes between corticol and trabeular with age
young
- corticol- thick cortices and large osteons
- trabecular- good connectivity
old
- corticol- periosteal apposition increases diameter, thin cortices, smaller osteons
- trabecular thinning and loss (especially interconnecting struts)
factors influencing variation
genetic- number of SNPs have been associated with BMD but have modest effects
nutritional- levels of calcium and vitamin D
hormonal- sex steroids particularly oesrogens
mechanical- physical activity, body mass - putting on weight can increase force on bone + strengthen them
fracture incidence
young men have higher risk of hand, ankle and wrist factures at a higher age- due to higher risk at activities at a young age
number of fractures increasing in 50s and takes off from this age (more in women)
more likely to be fragility fractures- due to everyday activity
more occur at trabecular bone- upper arm, pelvis, hip etc
osteoperosis
systemic skeletal disease characterised by low bone mass and microarchitectural deteriorateion of bone tissue, with a consequent increase in bone fragility and susceptibility to fractor
1 in 2 for women
1 in 5 for men
typical fractures- hip, vertebral and forearm
fractures often lead to loss of movement and individuals dont make it make to fitness before injury
forearm fractures often first sign of osteporosis
osteoporosis + BMD
can be found out by BMD measure
T score- no. of SDs below average
osteopenia- T score for hip/spine= BMD<-1.0
osteoperosis- T score for hip/spine= BMD<-2.5
