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osteo refers to bones and / osis means
pores so osteoporosis is when there's a
higher breakdown of bone in comparison
to the formation of new bone which
results in porous bones meaning a
decrease in bone density to the point of
potential fracture looking at a
cross-section of a bone there's a hard
external layer known as the cortical
bone and a soft internal layer of spongy
bone or trabecular bone that is composed
of trabeculae the trabeculae are like a
framework of beams that give structural
support to the spongy bone the cortical
bone in turn is made up of many
functional pipe-like units called
osteons which run through the length of
the bone in the center of these osteons
there are hollow spaces called haversian
canals which contained the blood supply
and innervation for the bone cells
around the haversian canals there are
concentric lamellae which look a bit
like tree rings the lamellae have an
organic part which is mostly collagen
and an inorganic part called
hydroxyapatite which is mostly calcium
phosphate in between neighboring
lamellae there are spaces called lacunae
which contain bone cells called
osteoclasts bone may appear inert and
unchanging but it's actually a very
dynamic tissue in fact spongy bone is
replaced every three to four years and
compact bone is replaced every 10 years
in a process called bone remodeling
which has two steps bone resorption when
specialized cells called osteoclasts
break down bone and bone formation which
is when another type of cells called
osteoblasts form new bone bone
remodeling as a whole is highly
dependent on serum calcium levels which
in turn are kept in the normal range by
a balance between parathyroid hormone or
PTH calcitonin and vitamin d parathyroid
hormone is produced by the parathyroid
glands in response to low serum calcium
and it increases bone resorption to
release calcium into the bloodstream
on the other hand kal
tonin is produced by the thyroid gland
in response to high serum calcium so it
opposes the action of PTH therefore
promoting bone formation and decreasing
bone resorption finally vitamin D
promotes calcium absorption in the gut
so it increases serum calcium promoting
bone formation and decreasing bone
resorption the balance between these
regulatory factors results in a peak
bone mass usually by age 20 to 29 and
this usually occurs earlier in females
than in males factors that determine the
peak bone mass are genetics for example
people of African descent tend to have
greater bone mass and nutrition meaning
adequate vitamin D intake increases bone
peak mass finally strength training
increases peak bone mass as well as
hormones like estrogen and androgens
that inhibit bone resorption okay now
when osteoclasts break down bone faster
than the osteoblasts can rebuild it it
results in the lowering of the bone mass
and eventually in osteoporosis if we
zoom in to a cross-section of an
osteoporotic bone it will show normal
cells with a normal mineralization which
differentiates it from osteomalacia
where there's a lack of mineralization
so with osteoporosis abnormal findings
include fewer trabecula in the spongy
bone and thinning of the cortical bone
as well as the widening of the haversian
canals these bone changes increase the
risk of fracture and they're known as
fragility or pathologic fractures some
bones like the vertebrae
shoulder blades and ribs consist mainly
of spongy bone so they're in great risk
of fragility fractures
factors that accelerate bone mass loss
and increase the risk of osteoporosis
our low estrogen levels like after
menopause and low serum calcium
additional factors include alcohol
consumption/smoking drugs like
glucocorticoids which decrease calcium
absorption from the gut through the
antagonism of vitamin D and drugs like
heparin and alpha rock scene another
factor is physical inactivity as seen in
astronauts in a zero-gravity environment
where they just don't use their muscular
skeletal system as hard as when they're
on earth as a result bone deposition
decreases due to a lack of stress while
resorption increases
there are also diseases that can cause
osteoporosis like Turner syndrome
hyperprolactinemia Klinefelter syndrome
Cushing's syndrome and diabetes mellitus
now the two most common types of
osteoporosis are postmenopausal
osteoporosis encina osteoporosis in
postmenopausal osteoporosis decreased
estrogen levels lead to increased bone
resorption with cena osteoporosis on the
other hand it's believed that
osteoblasts just gradually lose the
ability to form bone while the
osteoclasts keep doing their thing
unabated
so bone resorption usually overtakes
bone formation around the eighth decade
of life people with osteoporosis don't
usually have symptoms until a fracture
occurs the most common type of fractures
are vertebral fractures also known as
compression fractures and that occurs
when one or more bones in the spine
weaken and shatter vertebral fractures
caused back pain height loss and a
hunched posture femoral neck fractures
and distal radius fractures can also
occur and they're often associated with
postmenopausal osteoporosis osteoporosis
is usually diagnosed with a dual energy
x-ray absorptiometry or DEXA scan which
tests for bone density the test compares
an individual's bone density to that of
a normal adult which yields the result
or the t-score a t-score less than or
equal to negative two point five is die
gnostic of osteoporosis treatment for
osteoporosis usually relies on
bisphosphonate drugs like alendronate
and resent Renee if osteoporosis is
really advanced teriparatide a
recombinant parathyroid hormone can be
used
now even though parathyroid hormone
stimulates bone resorption it's been
found that intermittent injections with
teriparatide activates osteoblasts more
than osteoclasts therefore increasing
bone formation interestingly a thiazide
diuretic like hydrochlorothiazide can be
used to treat osteoporosis as well
hydrochlorothiazide boosts calcium
retention in the kidney and directly
stimulates osteoblast differentiation
therefore decreasing mineral bone loss
finally medications like DiNozzo map
which is a monoclonal antibody that
inhibits osteoclasts and raloxifene
which is a selective estrogen receptor
modulators
can be used for postmenopausal
osteoporosis all right as a quick recap
osteoporosis refers to decreased bone
density on account of increased bone
resorption compared to bone formation in
osteoporosis there is thinning of the
cortical bone widening of the haversian
canals and a decrease in the number of
trabecula in the spongy bone there are
two common types of osteoporosis
these are senile osteoporosis and
postmenopausal osteoporosis the most
common type of fracture in osteoporosis
is a vertebral compression fracture
diagnosis is done with the dual energy
x-ray absorptiometry or DEXA scan where
a t-score equal to or less than negative
two point five equals osteoporosis
first-line treatment relies on
bisphosphonate drugs like alendronate
Andrews Engine 8
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