When to start human growth hormone
Specific Hormones | Functions of Growth Hormone (hGH)
welcome back to the endocrine system on
catalyst University my name is Kevin
tole cough please make sure to like this
video and subscribe to my channel for
future videos and notifications in this
video we're going to be discussing the
functions of growth hormone or as it's
called in humans human growth hormone or
HGH now before we get into the specific
functions of HGH let's review a little
bit about how growth hormone is released
so up here at the very top of this image
we have the hypothalamus and then this
thing hanging down is the pituitary
gland and on the left side of it this is
actually the anterior pituitary gland so
recall that the hypothalamus generates a
growth hormone releasing hormone or GH r
h GH rh enters the hypothalamic
hypothesis pardal system this network of
blood vessels that carries GH rh down to
the anterior pituitary gland and GH rh
there stimulates the anterior pituitary
gland to generate HGH or human growth
hormone and another name for this that
you'll often see is somatotropin so if
you see this this is referring to growth
hormone and from the anterior pituitary
gland growth hormone is released into
the blood into the general circulation
where it travels to target tissues
now we're gonna see that it's gonna have
effects on tissues like adipose tissue
skeletal muscle bone and the liver but
before we get into all these specific
functions I want to go over the major
goal of growth hormone because this
major goal is really going to dictate
all the specific functions they all sort
of come back to this so the major goal
of growth hormone is to provide adequate
nutrients for ATP synthesis and protein
synthesis so if we think about all sorts
of peripheral cells like let's say
skeletal muscles skeletal muscles are
composed of cells that are going to be
metabolically active
in order to conduct metabolism you have
to have nutrients like glucose fatty
acids right and why do you have to have
those nutrients to make ATP because ATP
is what's going to allow that cell to do
work so in order to have ATP you have to
have nutrients and in order to get that
nutrients you need something that's
going to stimulate the body to allow for
the availability of those nutrients so
if you want to do work you have to have
ATP and if you want ATP you have to have
nutrients and so growth hormone is going
to make some changes around the body to
increase the availability of those
nutrients and the first two tissues
we're going to look at are the liver and
adipose tissue
now adipose tissue is just your body fat
and the body fat of course is going to
contain lipids in the form of
triglycerides so the first effect that
growth Warren's gonna have is on adipose
tissue where it stimulates lipolysis now
in general lipolysis is a process that
breaks down those triglycerides into
individual fatty acids and then those
fatty acids are released into the blood
well that makes sense given the school
because those fatty acids could be taken
up by skeletal muscle or other cells
that are metabolically active and used
to make ATP so lipolysis and adipose
tissues the first function next we're
gonna stop at the liver and see several
functions here okay now the liver is
gonna play a major role in increasing
blood glucose because glucose can also
go to cells that are metabolically
active for ATP synthesis and the way the
liver is going to do that number one is
by activating gluconeogenesis so the
liver is the major organ that performs
gluconeogenesis which is the synthesis
of glucose from non carbohydrate
precursors and so if the liver is making
glucose by this method
it's then I'm gonna take that glucose
and dump it into the blood and therefore
that glucose is going to be available to
all sorts of peripheral tissues the
second thing the liver is going to do is
glycogenolysis recall that the liver is
one of the two
major organs that's going to store
glycogen remember glycogen is a polymer
of glucose and so glycogenolysis is
breaking that glycogen down into glucose
and of course just like in the case of
gluconeogenesis the glucose that's
created through glycogenolysis is going
to be released into the blood where it
can then go and travel to peripheral
tissues and those tissues can take it up
and make ATP okay so the liver is
increasing blood glucose through two
major mechanisms one is through
gluconeogenesis and the second is
glycogenolysis now growth hormones going
to stimulate the liver to do one more
thing and that's going to be to release
another type of hormone called igf-1
Celyn like growth factors we're going to
come back to that at the end of this
video
so really the effects that growth
hormone has on adipose tissue and the
liver is to increase the availability of
nutrients in the blood specifically
glucose from the liver and mainly fatty
acids from adipose tissue and all those
nutrients are gonna travel in the blood
to tissues like skeletal muscle and bone
where they're gonna be taken up utilized
in metabolic pathways to make ATP and
that allows the cells to do work and one
example of a process that's gonna take a
lot of ATP is protein synthesis it's
gonna take a lot of molecules of ATP
just to make one protein and obviously
skeletal muscles as we learned in A&P
one are composed of lots and lots of
proteins okay but it turns out that
growth hormones also going to have some
other specific effects on cells of
skeletal muscle and bone let's explore
those so in skeletal muscle growth
hormone is going to stimulate glucose
uptake the way it's going to do that is
by increasing the number of transporters
in the membrane of the skeletal muscle
cells these are called glucose
transporters and if the muscle cells put
more glucose transporters in their
membrane they can uptake more glucose
and that's stimulated by growth hormone
also amino acid uptake is increased by a
similar mechanism and in conjunction
with the increased amount of eight
TP from all the glucose uptake the amino
acids can be strung together into
proteins and so overall growth hormone
is going to increase protein synthesis
all over the body but especially in
skeletal muscles okay so hopefully that
makes sense now let's take a look at
bones growth hormone also is going to
have similar effects on bones
first of all growth hormones gonna
stimulate increased glucose uptake into
the bone cells it's gonna stimulate
increased amino acid uptake into the
bone cells and again with that increased
uptake of amino acids in conjunction
with increased ATP synthesis you're
gonna be able to synthesize more
proteins so protein synthesis increases
we're starting to see a trend with
growth hormone the other thing that
we're also gonna see in bone is that we
have an increase in bone mineral density
so the more growth hormone a person has
the more dense their bones are okay and
this is important in preventing
osteoporosis one of the reasons why as
we age we have an increased
susceptibility to osteoporosis is
because growth hormone levels naturally
decline with age and so if you have less
growth hormones circulating in your
blood at any given time over time your
bone mineral density may actually drop
okay so increase bone mineral density
and then also during puberty whenever
your bones grow in length
remember that involves cartilage and the
synthesis of cartilage is termed Kandra
genesis so growth hormone also
stimulates Kandra Genesis okay which
helps bones grow in length so overall
what the growth hormone is doing is
through the adipose tissue in liver it's
increasing the amount of circulating
nutrients and then those nutrients are
taken up by cells like skeletal muscle
and a bone also growth hormone augments
the uptake of those nutrients like
glucose and amino acids but then through
metabolic pathways we get more ATP and
then we can build more proteins
okay now growth hormone can also do two
other things one is growth hormone can
actually stimulate the liver to Jen
another hormone that's released into the
blood and those are IGFs or insulin like
growth factors one of the most common
insulin growth factors is igf-1 which
would be termed somatic in one so IGFs
are also called somatic meetin's those
IGFs travel in the blood to all sorts of
peripheral tissues and they exert
functions there by binding to the
insulin receptor and overall what the
IGF s do is they increase glucose uptake
by those cells they also increase amino
acid uptake and they increase protein
synthesis really just as we saw over
here in the case of skeletal muscle and
bone except it's not directly growth
hormone that's doing that for a bunch of
other cells
it's the IGF the second thing that these
do is they can actually exert negative
feedback on the release of growth
hormone releasing hormone and so what
they do is if there's too much
IG F in the blood those IGS can then
circulate back and inhibit the release
of growth hormone releasing hormone
because if we have plenty of IGF s-- in
the blood that signals that not only do
we have plenty of IGF s-- we have plenty
of growth hormone and we don't need to
get any more growth hormone released so
IGF scan inhibit the release of GH RH
it's also worth noting that there's
another inhibitory hormone called growth
hormone inhibiting hormone or G H I H
and this can also exert a similar effect
to IGFs it will actually inhibit the
release of growth hormone okay so
hopefully this video gave you a good
comprehensive look at what growth
hormone is doing like I mentioned at the
beginning of the video it's really just
making sure that the blood has plenty of
circulating nutrients and then it will
also increase the ability of a lot of
these cells to uptake those nutrients
which then allows them to make more ATP
and have more protein synthesis and then
of course growth hormone also stimulates
the liver to release insulin like growth
factors which have similar effects on
all sorts of other cell types now this
is a really important topic to
understand for growth hormone
because in the next video when we cover
the functions of thyroid hormones what
we're gonna see is actually that they
are very similar in function very very
similar there's a couple differences
between the functions but we'll cover
those when we look at the thyroid
hormones in the next video so please
make sure to like this video and
subscribe to my channel for future
videos and notifications thank you very
much
