Thyroid hormone, primarily T3, exerts its effects by entering target cells, converting T4 to T3, and then binding to nuclear receptors that regulate gene expression, ultimately influencing cellular metabolism, growth, and function across various organ systems.
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all right Ninja nerds in this video
we're going to talk about the thyroid
hormone and it's exert its effects
exerted on multiple different Target
tissues all right so before we do that
we need to first see so we we if you
guys have already seen our video on the
synthesis of thyroid hormone you guys
are caught up because right now we have
thyroid hormone circulating in the
bloodstream right and if you remember if
we have thyroid hormone it was bound to
this protein that was made by the liver
and this protein if you remember was called
called
thyroxine binding globulins right it was
made by the liver and it was
transporting in it
T3 and T4 our thyroid hormone before we
look at how it's affecting all these
different types of Target organs we have
to look and see how it's actually
working in this cell what are the
mechanisms by which this hormone is
exerting its effects on these cells so
let's see
here let's say that we have T3 and T4
right here's what we got to look at T4
is going to be one of the ma more major
components in the blood okay so T4 is
one of the more major components within
the blood now watch what happens to this
T4 and again T4 is called
thyroxine T4 or
thyroxine has the ability to pass
through the lipid biler so look it
actually moves right through the lipid
Bay when the thyroid hormone gets into
this target tissue when it moves through
the lipid bilayer there's a specific set
of enzymes in this area one of these
enzymes that work specifically within
this area is called five Prime
Prime
D iio denas so it's called five Prime
deiodinase and what is this enzyme doing
it's removing an iodine off of what the
thyroxine specifically on the five Prime
carbon so this enzyme is removing a
specific iodine residue all right so now
let me actually show you exactly what's
happening here with T4 and this five
Prime deonat let me show it over here in
a better diagram so let's say here
here's my tyrosine amino acid if you
guys remember it was represented by that
big circle and here was another tyrosine
amino acid which was repres represented
by that big circle right now if I were
to be really really specific this circle
is technically a six carbon ring so I
could say 1 2 3 4 5 6 right same thing
over here 1 2 3 4 5 6 and if you
remember we had iodines popping off but
what actually what carbons are they
popping off well hey this is confusing I
have 1 2 3 4 5 6 1 2 3 4 5 6 these can't
be 1 2 3 4 5 6 and these can't be 1 2 3
4 5 6 I actually have to say this is
One Prime 2 Prime three prime four Prime
five Prime six Prime that way I
differentiate between these two so
technically the iodines are on the
three the five over here and then
they're on the thre Prime and the five
Prime so if I'm using an enzyme called
five Prime deiodinase I'm pulling off an
iodine which carbon am I removing it off
of this five Prime so imagine my hand is
going to rip this thing off that's what
this enzyme is doing it's ripping this
off when it rips it off of the five
Prime carbon guess what T4 turns
into it turns into
T3 the active form this is the active
form of the thyroid hormone the trio
thyronine right now there is another
enzyme that can rip it off the fifth
carbon what would he be called five diod
theas if that happened if I RI this
iodine off the fifth carbon this
wouldn't be T3 it would be what's called
reverse T3 which is inactive okay that's
inactive we have to remember that I know
it's something so small but it's very
very important five Prime deiodinase
rips the iodine off of the five Prime
carbon to make it T3 which is the active
if it's five deiodinase he pulls it off
the five carbon and turns them into
reverse T3 which is inactive okay now
that we know that we've got our active
form how is this going to exert its
effects it's going to come over here you
see there's a receptor waiting for him
look here's your
T3 he's waiting to start binding onto
this pocket there's a little pocket
let's say that this thing right here is
Factor well or even a receptor right so
this is going to act like a receptor but
it has a transcription Factor portion so
look what happens T3 comes over here and
binds on to this pocket but he can't
exert his effect on the DNA until
something else comes over here and binds
on this pocket guess what else comes
over here and binds retinoic acid
retinoic acid he comes over here and
binds into this pocket so what two
things are binding into this pocket one
is T3 binds right into that pocket the
other one is retinoic acid binds right
into the pocket then this transcription
factor is now active and it can move
into the nucleus and stimulate a
specific Gene sequence a hormone
response element so look what's going to
happen now it's going to come in
here and it's going to stimulate a
specific Gene sequence when it
stimulates that specific Gene sequence
this Gene will then undergo
transcription you know it'll undergo
translation and what will be the overall
result it'll result in
eventually protein synthesis look at
this protein that we're drawing here so
what is this thing here called This is a
protein so what was the overall result
T4 got turned into T3 T3 and retinoic
acid sometimes they even denote it just
in case you see it in the literature
it's also called
rxr it's just a short term abbreviation
for retinoic acid because this a
heterodimer binds into the actual
hormone response element the gene
transcribes the actual Gene to make mRNA
gets translated to make proteins look
what these proteins are going to do love
these proteins they're going to get
plugged into the membrane all across the
membrane look at this protein right here
this protein right here and we'll put
one more here just cuz they're
fascinating proteins look what these
proteins are going to do they love to
pump three sodium ions out of the cell
and they love to pump two potassium ions
into the cell so what would this one be
pumping out guys say it out aloud with
me three sodiums pumping out and then
two potassiums pumping in three sodium
out two potassium ions in these are
sodium potassium ATP Aces what did I
just say ATP Aces they require ATP so
for this step right here ATP has to
react and get converted into
ADP same thing here ATP would have to
react here and get converted into ADP
and and then same thing here ATP would
have to react here and get converted
into ADP what do you notice guys I'm
using a lot of energy I'm using a lot of
energy to power these pumps guess what
thyroid hormone's doing he's increasing
the expression of these proteins on our
body cells if we make more of these
proteins we have more sodium potassium
pumps if we have more sodium potassium
pumps we start burning the ATP so in a
result what's going to happen to the ATP
levels here you're going to have a
decrease in cellular
cellular
ATP now if you if you guys think about
it since we already know this I'm going
to erase this guys since you already
know that ATP is a product of
metabolism if our if our ATP is going
down that's not a good thing why because
then we can't power the muscles we can't
power these pumps we can't power a lot
of cellular activities so what do we
need to do then we need to start burning
more fuel so what's going to happen
happen if you have a decrease in
cellular ATP what's that equation guys
for cellular respiration it goes C6 h126
plus six oxygen to yield what is it 6
CO2 plus six water right and then as a
result you're making ATP in heat right
this is a result of that
reaction well the ATP is decreasing so
we need to make more ATP so what are we
going to do we're going to provide more
fuel so what's going to happen then
we're going to start burning more
carbohydrate molecules or fat molecules
or protein molecules right and we're
going to use more oxygen for this
Pathway to occur so what starts
happening to the amount of oxygen it's
going to increase in usage so there's
going to be an increase in oxygen
usage and if there's an increase in
oxygen usage it's not just good for
burning carbohydrates but also good for
burning all different types of uh
macromolecules so in in summation what's
going to happen to the overall
metabolism or the metabolic rate it's
going to go up okay not that bad right
guys so increase in metabolic
rate and if you think about it if this
metabolic this reaction is occurring
excessively what else am I going to
produce a lot of a lot of heat and so
when you're producing a lot of heat what
else are you going to notice you're
going to get a little hot right so again
it's going to have a increase heat
production as a result of an increase in metabolic
