all right hello all this is Dr. Alsup again and in this video we will be discussing
factors that affect bone so really what we're getting into are the specific
structures such as minerals, vitamins, hormones that can play a role in terms of bone resorption
or bone deposition but also importantly bone remodeling so we talked a little bit about
that in a previous video so we'll let's talk about these specifics in a bit more detail
okay so you can't talk about this without obviously talking about the minerals that
are playing such a huge role here and this should really make intuitive sense we know that we really
can't have that extracellular matrix without these important minerals in particular and that's why
i have an asterisk here is calcium calcium is going to play a huge role with phosphorus
playing a lesser role and i do have a few other ions here magnesium fluoride manganese that will
play a much smaller role but it's really these two that i want us to to remember are going to
play a role so you're going to have these kind of stored within bone and then in certain scenarios
either it's going to stay stored within bone or it could be released from bone
to to increase but blood calcium levels so we'll talk about some of the things that will cause
that to occur in a moment so really focus in on these two here okay now let's move on to vitamins
now and vitamins are going to be very important there's more than just the two that we're going to
talk about that will play a role but i really want us to focus in on vitamin c as well as vitamin d
because they're going to play the bigger roles okay so let's start with vitamin c this is needed
for the production or the synthesis of collagen and we know collagen is hugely important as the
organic material that's going to play such a big role in terms of the extracellular matrix
so if you have an insufficiency of vitamin c that can have pretty great effects in
terms of bone growth or even delay in terms of fracture repairs so vitamin d is very important
vitamin c excuse me vitamin d is a hugely important one um so the active form of vitamin
d is referred to as calcitriol okay and calcitriol is produced by this sequential action of numerous
organ systems so it's going to kind of start in terms of the skin it's going to have various
different functions throughout the liver and the kidneys so it's really kind of
the sequential action of the skin liver and kidneys that are going to create calcitriol
and you're going to discuss that development in these various organ systems in other blocks but
what we want to talk about here in terms of calcitriol is that it can play a big role in
terms of increasing blood calcium levels okay so increasing blood calcium levels um and it
can do this by increasing calcium absorption by the small intestines or the kidneys or calcium
resorption from the skeleton to releasing calcium as well as phosphate ions from the reservoirs
that occur in bone so vitamin d and its active form calcitriol can play a hugely important role
now let's get into the fun stuff let's talk hormones now and we're going to start with
calcitonin sometimes you hear it just abbreviated to CT which is not the same thing as that
similarly named calcitriol that we just talked about a moment ago so calcitonin calcitriol are
very different structures so calcitonin is a hormone it is going to be secreted
by the endocrine thyroid gland the thyroid gland your largest endocrine and calcitonin is going
to inhibit bone resorption okay so inhibiting bone resorption or in other words it's going to inhibit
osteoclasts from breaking down bone and releasing calcium into the bloodstream so it's really going
to um it can play a role in terms of decreasing blood calcium levels calcitonin plays a huge role
in childhood but a lesser role when we get into adulthood okay so this is the
one that's really going to inhibit bone resorption now parathyroid hormone or PTH
which is secreted by parathyroid glands that are located on very in very close association with
the posterior thyroid gland so it's not the same thing as the thyroid gland and this is
really evident in terms of what the hormones do so whereas calcitonin would inhibit bone resorption
parathyroid hormone will promote bone resorption and thus increase blood calcium levels
okay so they have opposite roles basically in terms of the hormones that are secreted
by those very closely associated glands all right so PTH will promote bone resorption by osteoclasts
which will allow calcium to be released into the bloodstream or into as well as
inhibiting collagen synthesis by osteoblasts so it can actually inhibit bone deposition
it also has as you can see here important roles in terms of the gastrointestinal and renal systems
and there'll be more to come on that but really these two hormones play very opposite roles in
terms of what will happen with blood calcium levels or whether osteoclasts are going to be
inhibited or if they're going to be promoted all right um so that's so that balance is really
important the delicate balance but that balance will play a role in terms of just making sure
that the the appropriate blood calcium levels are present in the body okay other hormones
can play a role in bone growth and remodeling but they're not playing quite as huge a role as this
does throughout life but they can play really big roles at certain periods of life so one of these
one of these examples are going to be sex hormones such as estrogen and testosterone both of which
can stimulate osteoblasts so particularly in terms of time where there is bone length growth so it's
going to play a really important role there so it can promote osteoblast activity into adulthood
it also can play a role in terms of bone remodeling throughout life
now human growth hormone or hGH is going to be a hormone that's secreted by the pituitary gland
it really just plays a role in terms of general growth of all body tissues so obviously that
includes bone as well so i thought i would mention that here other factors can affect bone growth and
remodeling like exercise weight-bearing activity can really stimulate osteoblasts and that aging
process to change and but also bone remodeling generally osteoclast activity tends to outpace
osteoblast activity so you really need to work through methods that will increase osteoblast
activity such as weight-bearing activity so to really keep away from having that
decreased bone mass with the inequity of osteoblast and osteoclast activity
all right excellent so those are the big picture concepts that i wanted to get across regarding
bone or what's affecting bone so let's review a question all right so if blood
calcium levels are low which hormone may be secreted in order to maintain homeostasis
so these are for all hormones you have calcitonin, human growth hormone, PTH, or testosterone
and really pause the video try to figure this out on your own and when you're ready let's hone in on
certain parts of this stem so it says blood calcium levels are low
okay so what needs to happen is that there needs to be an increase in blood calcium levels
and really one of these hormones will initiate osteoclast activity that will
break down bone and allow for calcium that's stored in bone to be released into the bloodstream
and really only one of these is going to do that and that is c parathyroid hormone or PTH
and so this will serve to increase blood calcium levels by initiating osteoclast activity
the others are going to be examples of things that will play a bigger role in terms of bone growth
it can initiate osteoblast activity but pth is really the major one in terms of
functioning to hopefully keep it homeostasis if blood calcium levels are low to cause for
blood calcium to be released into or cause calcium to be released into the bloodstream
and that can be a good thing you want that you need calcium in order for say muscles to
to contract appropriately or for neurons to be able to communicate with one another so
that's a very natural important thing it's when you have too much osteoclast activity with
without that kind of even osteoblast activity as well and that's where you
get out of homeostasis and we'll talk about a few examples of that in upcoming videos
okay excellent so these are all really cool things that we are introducing here and in
certain cases particularly some of those hormones they'll come back in later portions
of the course as well when you get to those organ systems i want to thank you for your
time and attention and as always always please reach out if you have any additional questions