hello all this is dr alsup and in this video we will be discussing the factors that can
affect bone growth not only in juveniles but as well as remodeling a bone in adults
excuse me so these factors that we're going to discuss can speed up bone growth or slow them down
and we will talk some basics here we will also talk a little bit about bone remodeling as we have
spent considerable time discussing bone growth but bone remodeling plays such a vital role in
a healthy functioning skeletal system throughout life so we should give it its due here as well
all right so let's begin our discussion of factors that affect bone growth with the all
important minerals and we know minerals this is going to make intuitive sense because minerals
are vital in extracellular matrix calcification so that organic material is good and all but you
need those minerals to calcify or harden in order to have a robust hard bone that we know and love
so in particular calcium i have this little asterisk here so you know that that's a good
one but also phosphorus is going to play a role in making the extracellular matrix hard
other minerals such as these described here like magnesium fluoride manganese they'll
play smaller roles in strengthening and forming the extracellular matrix
so in other words really hone in on calcium here and to a lesser extent
phosphorus in terms of the importance of the extracellular matrix calcification
all right vitamins also are important to bone and more than just the two that we have here
are going to play a role but i do want to kind of pull our focus to two vitamins vitamin c and
vitamin d vitamin c is needed for the production or synthesis of a collagen
which we know is very important in the organic materials of the bony extracellular matrix
so if there's an insufficiency of vitamin c it can stunt bone growth or delay fracture repair
now let's talk vitamin d and vitamin d is going to come up over and over again throughout the course
the active form of vitamin d is called calcitriol
where do i have that written here yeah here it is calcitriol and um this involves
the it's pretty complex first of all calcitriol is complex uh it involves the skin and kidneys
of which you will discuss some of those details in those upcoming lectures later in the course
but calcitriol for our purposes there it's going to help in terms of building bone by allowing
increased absorption of calcium from other areas so particularly that gastrointestinal tract
into the blood so calcitriol is going to play a role in terms of increasing absorption of calcium
now let's talk hormones because some of these are extremely important in calcium homeostasis
which can initiate certain bone cells so starting with calcitonin or ct which is not the same thing
as that similarly named calcitriol so calcitonin is a hormone secreted by the thyroid gland
which you can see here on this image the thyroid gland is actually your largest endocrine gland
and calcitonin will inhibit inhibit bone resorption all right so inhibit bone breakdown
or in or in other words inhibiting osteoclasts so from breaking down the bone and releasing calcium
into the bloodstream so keeping the calcium stored in bone the parathyroid hormone or pth
which is secreted by the parathyroid glands which are actually located just posterior to
the thyroid gland you can see that this is a posterior view here this is an anterior view
so on the back of the pair of the thyroid glands you'll have the parathyroid glands
so the parathyroid hormone or pth actually has the opposite effect of calcitonin it will promote bone
resorption so it will that bone resorption by the osteoclast so allowing calcium to be released into
the blood um so calcium uptake can increase in certain certain other organs particularly in terms
of the intestines bth will also actually promote the formation of calcitriol so kind of coming
full circle there so key here calcitonin and parathyroid hormones kind of have opposite effects
so the balance between these hormones is delicate but it's very important in terms
of calcium homeostasis other hormones can play a role in bone growth um
specifically sex hormones estrogen and testosterone both of which can stimulate
osteoblasts particularly during those times that we like to refer to as a growth spurt but it will
also promote osteoblast activity into adulthood so during bone remodeling and it can play a role in
terms of slowing bone resorption and lastly human growth hormone secreted by the pituitary gland
causes just general growth to all body tissues including bone so need to include it here as well
other factors can affect bone growth like exercise in which weight-bearing exercise can stimulate
osteoblasts and the always intimidating aging process in which osteoclastic activity tends
to outpace osteoblast activity thus decreasing bone mass so this brings up a bone remodeling
which occurs throughout life and is simply put the replacement of old bony tissue with new fresh bony
tissue and this is a very natural process you want this to happen you want it to occur throughout
life and it will involve the functioning of both osteoblasts as well as osteoclasts and you want
these working in unison things get dangerous when one set works faster than the others
so you want that that natural delicate balance between the osteoblasts and osteoclasts
spongy bone is replaced considerably faster than compact bone it takes a while to
fully replace compact bone in certain areas all right in our next video we will discuss aging in
bone and osteoporosis which typically typically occurs when these components are not working in
unison so those osteoblasts and osteoclasts or certain ones are working slower than you need
but before we do that let's review a concept question if blood calcium levels are low
which hormone may be secreted in order to maintain homeostasis is it a calcitonin
b human growth hormone or hgh c parathyroid hormone or pth or d testosterone all right a
key here in the stem is that blood calcium levels are low all right so the blood calcium levels are
lower wanting to maintain homeostasis so in this case the body needs to move calcium out of storage
which we know the storage is occurring in bone and get it into the blood so we need to break
down bone or initiate osteoclast activity so which hormone as these are all hormones will do this
and hopefully you are settled on the fact that c or para thyroid hormone is the correct answer
this is what's being secreted by the parathyroid glands and this will initiate osteoclast activity
the other hormones that are your distractors here will typically initiate osteoblasts
not osteoclasts so c parathyroid hormone is the correct answer okay i love love love this
question it is pretty indicative of the type of question you may see on the exam thank you for
your time and attention here and please always feel free to reach out if you have any questions