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


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