This content provides a detailed anatomical and functional overview of the hypothalamic-pituitary axis, focusing on the distinct origins and hormonal roles of the posterior and anterior pituitary glands.
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all engers what we're going to do in
this video is we're going to talk about
the hypothalamic and the pituitary axis
so if you look here at this diagram
first off let's kind of get some Anatomy
straightforward here if you look I'm
taking a piece of the hypothalamus in
the pituitary gland out of this overall
diagram here so if you look here I have
the cerebrum right or the tlon then I
have the cerebellum midbrain pwn medulla
spinal cord right what I'm doing is I'm
taking this piece out right here where
the hypothalamus and the mammilary
bodies in the infundibulum and the
posterior and anterior pituitary gland
are and we're zooming in on it so again
this whole chunk of gray matter right
here is the
hypothalamus this stalk part here that's
connecting the hypothalamus to the
actual pituitary gland is called the
infundibulum and then again back here is
going to be the poster pituitary gland
they also call the neuro hypothesis and
this one right here is going to be the
anterior pituitary gland or the adino
hypothesis all right first off before we
even get into anything real quick I want
to make sure that we understand where
this is actually situated so you know
this area right here there's a there's a
bunch of nuclear that are actually kind
of clustered together here hypothalamus
then you have What's called the thalamus
right there and then right back here
you're actually going to have another
part of it which is going to be the
epithalamus which is made up of the
pineal gland and the habenula and
habenular commiss and stri medular whole
bunch of different structures here that
are making up the diyon so he is the
hypothalamus is a bunch of gry matter
nuclei situated anterior to the thalamus
right anterior and a little bit inferior
to the thalamus so now we know where the
hypothalamus is and again the pituitary
gland is hanging from the hypothalamus
connected by the infundibulum one more
thing and then we're going to go ahead
and Dive Right In if I were to zoom in a
little bit bit more over here real
quickly I'm going to say here's the hypothalamus
hypothalamus
infundibulum I'm going to draw two
components here one is actually going to
be the poster pituitary gland the other
one I'm going to draw in blue this is
going to be the anter pituitary gland
now why am I talking about this really
quickly and why did I draw out another
color the poster pituitary gland the one
in black here that's actually going to
also be called the neural hypothesis
it's made up of neural tissue okay they
also call pites right so again it's made
up of nervous tissue this blue part
right here the anterior pituitary or the
Adeno hypothesis is made up of a
glandular cuboidal likee epithelial
tissue and it actually comes from the
actual ferx so it comes from the mucosa
of the ferx it's actually derived from a
Keys
pouch okay so it actually is derived
from the actual FX and it actually buds
off from the ferx and actually combines
with the posterior pituitary to
collectively form the anterior posterior
pituitary gland or together we call the
pituitary gland or another name for the
pituitary gland is the hypothesis okay
so now that we got that straight that's
good so again we know that the anterior
pituitary is glandular cuboidal
epithelia tissue derived from the ferx
Via what's called wrath Keys pouch and
we know that the poster pituitary gland
is actually neural tissue it's made up
of py so it's not really even considered
to be um a separate type of gland it's
not really considered to be an endocrine
gland it's actually a part of the actual
brain if you think about it okay now
that we've done that let's go ahead and
dive in let's first focus on the poster
pituitary gland and their hormones and
then we'll look at the anterior
pituitary so up here in the hypothalamus
there's some specific nuclei what is a
nuclei nuclei are going to be a group of
cell bodies right so in other words this
is the cell body here and you might have
dendrites coming off of it right so the
group of cell bodies collectively
together is called a nucleus in the
central nervous system and then there's
what's called attract and a tract is a
bundle of axons grouped together in the
central nervous system so in the
hypothalamus I have a bunch of nuclei
situated all over the hypothalamus we're
going to focus on very few of them we're
going to focus on this one specifically
first so what is this blue nucleus
called this blue nucleus is actually
called the Supra
Supra optic
optic
nucleus so it's called the supera optic
nucleus so the super optic nucleus is is
again a group of cell bodies
collectively joined together in a
specific area which is
unmyelinated and it's actually going to
be gray matter this is called the super
optic nucleus what does the super optic
nucleus do it makes a specific hormone
and and that hormone is actually going
to be carried down this what is this
this axon right here it's traveled down
the axon is transported down the axon by
specific types of motor proteins and as
you transport the actual vesicles down
here is these little vesicles containing
the specific hormone that's already been
pre-synthesized we're just Wai waiting
for a stimulus to release it that
hormone is called the anti dtic hormone
so okay now that we know we're going to
secrete what hormone are we making here
diuretic
hormone also referred to as short-handed as
as
ADH sometimes they even call it another
name I'll write that one down to it's
also called Vaso
Vaso
pressin so sometimes they also call it
vasopressin so again super optic nucleus
is secreting a specific hormone called
the anti dtic hormone but we said it's
already been presynthesized it's already
formed and sitting in these little
synaptic vesicles what triggers this
super optic nucleus to produce Action
potentials that move down the axon and
Trigger the release of this hormone
okay one big thing that actually can
trigger this effect here is is actually
going to be low blood volume so one of
the big ones is actually going to be low
blood volume all right so one big thing
is going to be low blood volume and if
you you have low blood volume what else
does that actually correlate with it
correlates with low blood pressure
because volume is a direct indicator of
pressure so low blood pressure will be a
very strong stimulus of these super
optic nucleus here okay what else
another big big big one is the plasma
osmolality okay so another one is the
plasma osmolality and specifically for
this one high plasma osmolality High plasma
plasma
osmolality so what does this mean by
high plasma osmolality well osmolality
is referring to basically the
concentration of solute inside of the
plasma and water so it's the
concentration of certain types of
electrolytes and solutes and water
inside of our blood plasma the higher
the plasma osmolality the less water
there is the more hypertonic it is the
lower the plasma osmolality what's that
mean that means that it's actually going
to be hypotonic so if it's again if it's
high plasma osmolality that means that
there's a lot of solutes very little
water it's hypertonic if it's a low
plasma osmolality what does that mean
that means that there's a lot of water
and less solutes so if there's a high
plasma osmolality that means that
there's very
little low
water High
solutes okay
this super optic nucleus actually has
specific things called osmo receptors
that are situated around it we're not
going to talk about those they that's be
called the subicular organ and the organ
vasculosum of lamin terminalis they're
basically osmo receptors that pick up
the plasma osmolality whenever it's high
it's going to stimulate this guy to send
action potentials down and release ADH
one other stimulus that's another
important one is also pain so pain also
has the ab ability to activate
the production of anttic hormone now
once we've produced this anttic hormone
it's going to go and exert its effects
on two different Target organs that
we'll talk about individually in another
video okay but again one more time pain
can stimulate the super optic nucleus
low blood pressure or low blood volume
and a high plasma osmolality which means
low water high amounts of solutes right
and who can pick up that change in
osmolality The osmo receptors like the
subicular organ or the Organo vascul
vasculosum of laminat terminalis and
where stimulated it sends the action
potentials down the axon and sends this
actual release of anttic hormone out all
right and then it's going to go affect
its Target organs what can inhibit so we
know it stimulates it what can inhibit
it one thing that can inhibit it is the
opposite effect so if you have what high
blood pressure if you have low plasma
osmolality what else is another really
big one alcohol so another really really
big effector of this is alcohol alcohol
actually has a inhibitory effect on ADH
okay so it has an inhibitory effect on
ADH and again what other things could
have an effect here like I said it could
be high blood pressure so I put High BP
or low plasma osmolality which I'm
denoting here as po
okay so again high blood pressure low
plasma osmolality and alcohol are some
very strong Inhibitors of anttic hormone
okay now that we've done that let's move
on to the next one what is this nucleus
that's situated right here called this
one is called the
the par
ventricular
nucleus okay so what is this one called
here this is called the par of
ventricular nucleus and both of these
are actually PA of ventricular nuclei
this one is and this one is so again
this these two could actually be having
their axons combined so I could actually
draw from this guy I could actually say
that these two axons are actually
combining here and when they combine
they form again what's that called
attract okay so these two guys could be
combining here all right so the
paraventricular nucleus it has these
axons that extend all the way from the
hypothalamus to the actual posterior
pituitary and it releases a very very
specific hormone in response that
because same thing like ADH the hormones
are stored in the synaptic vesicles in
the axon terminal so they're already
pre-formed and synthesized we just need
to stick stimulus to cause the release
so again what's this hormone that's
oxytocin okay so we call it oxytocin so
oxytocin is a very very important
hormone that again we'll talk about its
effects in an individual video and all
of its T Target organs but let's just
say what stimulates his release he
stimulated he stimulates these neurons
here so let's say what stimulates this
guy here so what stimulates here let's
actually do this in green so we can see
it here so let's say we have here what
stimulates this nucleus what's a
stimulator of that nucleus a stimulator
of this nucleus is usually going to be
the birthing process so one big thing is
the birthing process and like I said
I'll explain this in more detail when we
talk about in individual video so the
birthing process is a really really big
one another really big effector of it is
actually going to be suckling
so when the baby is actually suckling on
the mother's uh mammory glands or
specifically the areola it's actually
suckling on the nipple it can activate
specific receptors that will send the
actual release of oxytocin another thing
is actually going to be for the male
sexual ejaculation response so it's also
responsible for
ejaculation so all of these things are
very very strong stimulators of oxytocin
and again what are they the birthing
process suckling and ejaculation again
we'll talk about these in more detail
but again what happens stimulates the
par of ventricular nucleus he sends
Action potentials down calcium rushes in
and stimulates the release of oxytocin
so again posterior pituitary hormones are
are oxytocin
oxytocin
and anttic hormone are also called baso
press all right now that we've done that
for the Post tier pituitary let's go
ahead and look at the actual hormones
released by the anti pituitary in a
deeper way so over here you're going to
notice what do I have here I have I have
a nice vascul I have a blood vessel a
blood vessel connection a vascular
connection between who between the
hypothalamus and the anterior pituitary
gland whereas over here in the posterior
pituitary what was connecting the
hypothalamus to the posterior pituitary
these axons so there's a neural
connection now we need to Define what is
this neural connection right here that's
extending all the way from the
hypothalamus to the
actual posterior pituitary what is this
neural connection called this neural
connection is called the
fical
tract okay so let's define that again
let's basically work these words out
hypothalamic it's coming from the
hypothalamus to the hypothal what does
that mean the hypothesis hypothesis is
another word for the toer gland right so
it's going from hypothalamic hypohyal
it's a tract what is a tract it's a
bundle of axons in the central nervous
system so again this connection that's
connecting the hypothalamus to the
posterior pituitary gland is called a
hypothalamic hypop faial tract which is
a nerve connection all right whereas
over here if you notice this part of the
there's like a capillary bed on this
side there'll be a capillary bed down on
this side and there's a portal vein
connecting it we say by definition
whenever there's two capillary beds
connected in series between an
intermediate portal vein this is called
a portal system well it's a portal
system for what the hypothesis so this
right here is called the what's this
portal system here called This is called the
the hypo
hypo fisal
fisal portal
portal
system and again what is the hypop hypop
faal portal system it is again going to
be two capillary beds this is the
primary capillary plexus this one down
here is the secondary capillary plexus
and they're connected in series through
an intermediate portal vein and what's
that portal vein called the hypop fesial
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