This content provides a concise overview of the hypothalamic-pituitary-thyroid axis, detailing the hormonal cascade from the hypothalamus to the thyroid gland and the subsequent effects of thyroid hormones (T3 and T4) on various target organs, along with their negative feedback regulation.
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all right ner so we talked about the
thyroid gland in super great detail we
covered things in so much detail that
what I wanted to do in this video was
just give us a nice little overview of
that entire video so let's go ahead and
Dive Right In so if you look here we're
going to start the hypothalamus so if
you remember in the hypothalamus there
was specific neurons right that were
actually releasing the specific chemical
and what was that chemical that they
were secreting that chemical was called
thyrotropin releasing hormone and if you
want the nucleus was called the par
ventricular nucleus right what was that
TR doing it was flowing through the
hypophysial portal system which was just
a vascular connection right here right
so here's a little vascular connection
it was flowing through that where down
into the anter pituitary and in the
anterior pituitary there was some
specific cells right there what were
these cells here called these were
called thyrotropes right and these
thyrotropes were responding to the TR
and what were they secreting they were
secreting what's
called thyroid stimulating hormone right
so the first step was TR Second Step was
TSH what's the next thing well now we
have the thyroid gland well what has to
happen is the thyroid stimulating
hormone is going to circulate down
through the blood to the thyroid gland
and then it's going to act on the
thyroid gland when it acts on the
thyroid gland if you remember we said
that the overall result of this was the
production of T3 and T4 which stands for
our thyroid hormone right and then we
said that it's transported in the
bloodstream through the thyroxine B
globulins right and exerts its effects
on various different Target organs which
we're going to talk about in a brief
second here what I want to do is so now
that we understand this what's called
hypothalamic pituitary thyroid axis
let's say something real quick about
what happens whenever you have too much
or too low how does this affect it so if
you think about it for a second let's
say that your TH levels are high your
thyroid hormone levels are high what
does that do so let's draw here in
red it can actually circulate back up to
the hypothalamus and exert what's called
a negative feedback mechanism what does
that mean it inhibits the
paraventricular nucleus from making TR
if you don't make a lot of TR what do
you not make a lot of TSH if the T TSH
levels drop do you make as much T3 and
T4 no okay so high T3 and T4 negative
feedback low TR low TSH and then as a
result low T3 and T4 what about the
opposite if you have low T3 and T4 what
is it going to do it's going to exert a
negative feedback mechanism on the
paraventricular nucleus cause excessive
amounts of TR produce excessive amounts
of TSH and then the high amounts of TSH
will stimulate the increase in T3 and T4
so simple as that all right now that
we've done that let's look at the
effects of T3 and T4 on these various
Target organs and like I said we've
already gone into all of them in great
detail so we're just going to get the
overall look what was its effects on
bone it just promotes normal bone growth
so it promotes normal bone
growth and
maturation so it helps with being able
to promote normal bone growth and
maturation guess what else it does it
promotes normal muscular system
development and function so it promotes normal
normal muscular
muscular
function and
development okay what about on just
normal body cells do you remember it
increased the basil metabolic rate by
increasing the sodium potassium ATP AC
so it increases your basil metabolic
rate it increases the oxygen
usage and then it actually can cause
more metabolism right what are some of
those metabolic pathways that it it does
so it can actually do what's called
lipolysis it can actually do what's called
called
glycolysis and it can even do another
process which is called glucon neo
genesis so it's actually a hyperglycemic
hormone right because it has the ability
to increase blood glucose levels via
gluconeogenesis and it can break down
substance because your basil metabolic
rat is increasing you want to break down
a lot of glucose so there's a lot of
glycolysis and helps to break down fat
oh one more that I want to mention here
which is really really important is
helps with what's called
LDL uptake so LDL is a cholesterol it's
called lipo density low density
lipoprotein and it actually is bad
cholesterol so if we what it helps to do
is get a lot of that bad cholesterol out
of the blood and into our liver cells
right so it helps to increase the LDL
uptake which helps to lower the actual
cholesterols within the
plasma okay so that's its effects there
what does it do on the Heart It promotes
normal
cardiac output right so cardiac output
and different types of other functions
right all right what about in the brain
it promotes normal nerve development so
it promotes the actual increase in the
synapsis so what does it do it increases the
myelination it increases the
dendrites so all of these things are
helping to do what increase the actual
nervous system development and function
so it helps to be able to promote these
activities what does it do on the GI
tract it promotes normal GI motility and
function so it promotes motility so
contractions so it promotes
motility and secretions of the GI
tract and then again what does it do to
the scan it promotes the normal
hydration of the skin so it promotes
promotes normal
normal
hydration of the skin okay so if we
understand this this is the basic
overall function of thyroid hormone so
what happens TR is regulating the
production of TSH by the anterior
pituitary TSH is acting on a thyroid
gland to produce thyroid hormone and
thyroid hormone can produce bone growth
and maturation normal muscular function
and development increase our basil
metabolic rate and oxygen usage and it
can undergo lipolysis mechanisms
glycolysis mechanisms gluconeogenic
mechanisms and it can increase the
uptake of ldls low deny Lio proteins
promotes normal cardiac output and
pumping functions increases the synapsis
and the myelination and the dendrites
within our central nervous system and it
helps to promote normal motility and
secretions of the gastrointestinal tract
and promotes normal hydration of the
skin tissue so in that in a n sh that
gives us the functions of thyroid
hormone and also again knowing what
happens when there's elevated levels of
thyroid hormone what does it do it works
through a negative feedback mechanism to
inhibit the paraventricular nucleus to
stop making TR but if the thyroid
hormone levels are low it'll work
through the negative feedback mechanism
to stimulate the pair of ventricular
nucleus to make TR and then more TSH and
then more thyroid hormone all right
engineer so this was an overview on the
thyroid hormone I hope this made sense
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