We're going to talk about
antidiuretic hormone. And you can see I've already
started drawing for this video. And the main reason is because
I'm not a great drawer, and I wanted to make sure that
everything was pretty clear. And so I drew out on one
side the pituitary gland and on the other the brain. And so antidiuretic
hormone-- I underlined ADH because that's usually
what it's called. People call it ADH. Sometimes people call
it vasopressin as well. Actually, vasopressin is
good because it's useful. You can see "vaso" kind of
refers to blood vessels, and "pressin" kind of squeezing
down on blood vessels. It gives you a clue as to
what the hormone is doing. So I've drawn for you
the hypothalamus here. Also, right below
it, this would be kind of the infundibulum,
kind of the neck. And at the very
bottom, the pituitary. So this is the actual
pituitary down here. And there's a front
and back to this. And the front, facing
forward closer to the eyes, would be the anterior pituitary. So that'd be over here. And back here, this lobe would
be the posterior pituitary because it's a little
bit further back. And since we're
naming stuff, let me just go ahead
and round it out. This right here is
actually the optic chiasm. It has to do with vision. So I'm just going to
write optic chiasm so you know what
we're talking about. And the only reason
I even bring that up is because just above it--
let's say in this area-- just above it. And if I was to draw it
over on my little diagram-- that'd be maybe right there--
is what's called the "supra"-- S-U-P-R-A-- supraoptic nucleus. And nucleus here just
refers to a collection of nerve cell bodies, not
the nucleus we usually think of-- meaning not the
one where it's sitting inside of a cell and kind of
directing the flow of traffic in the brains of the cell
in a way of saying it. But here the nucleus is
actually just a collection of little nerve cell bodies. And I'm actually just
going to draw two, but you know there's
actually many more there. This is just for
diagram purposes. And actually, if I was to
draw the rest of this nerve, you would actually
go all the way down. And this is actually beginning
to share with you some of the cool aspects of this
hypothalamus and the posterior pituitary. You can see that, basically,
these nerve cells start in one spot, and
they go all the way down to the posterior pituitary
through that infundibulum. This is how the hypothalamus
and posterior pituitary are connected-- through nerves. And these nerves are actually
full of the hormone ADH. So we've already
talked about the fact that this is related to ADH,
but now you can see exactly how. ADH is actually being
made in these nerve cells. And it's actually
sitting here waiting for the right moment for
these nerves to release it. And this ADH is actually
a small protein. It's nine amino acids long. So it's actually pretty small. This is ADH. Nine amino acids. So it's pretty teeny,
and it's a hormone. And if you know it's an
amino acid-based hormone, you can think of it as a
peptide or a protein hormone and distinguish it from
the steroid hormones. So this is how ADH is made. It's made in these nerve cells. And the next thing to talk
about is how it's released. And so if you have, let's
say, a little capillary bed in here with little
arterials and capillaries coming together into little
venules on this side, what happens is that, when
there's a trigger-- and actually, maybe
I should write that in a very bold color. Let's say red. That's my favorite bold color. When there's a trigger,
these nerve cells right here are going to fire off their ADH. They're going to
release all that ADH, and it's going to dump
right here into this area where all the capillaries are. And of course, the
flow of blood is going to carry all that
ADH into the little vein-- and let me draw the
venule and the vein-- and basically, take it
to the rest of the body. So this is how ADH
actually gets released out of the nerve cells that live
in the supraoptic nucleus and gets out to the body. It basically does it by dumping
into that posterior pituitary and getting picked up by
all those little capillaries and venules. So I guess the next issue is to
figure out what is the trigger? So what is the trigger for
this little supraoptic nucleus that I've drawn here? So let's talk about that. Let me make some space. There. Now, we've got a
clean bit of canvas. So let's talk about the
triggers that our body uses to know when to fire off
that ADH to get it released. The main trigger-- and this
is probably the one trigger that you want to take away. If you're going to
forget everything else, try to remember this one. The main trigger is going to
be high blood concentration. And the way we think about blood
concentration is in osmolarity. Let me write that down. What osmolarity refers to is,
if you took all the solutes that are floating around
in the blood-- so that includes everything
from protein to sodium to potassium, everything
that is going to drag water into the blood vessels--
if you combine all that, then what is your total blood
concentration going to be? And you can almost
think of it as a meter. So let me draw it for you. Like a little meter here. On one side, you've got--
let's say something like that. And on one side,
let's say you've got 260, and on
the other side 320. And this is just concentrations. So 280 and 300. And this is osms per liter. And actually, these
are the units here. So osmolarity as measured
in osms per liter. So this is the concentration. And what you want
to do is you want to really stay in
this area right here. This is kind of your green zone. This is where the body likes
to be, generally speaking. And if it's here, if
it's in this area, or if it's in this
area, then that's where the body is not too happy. And so for example, let's say
you're in this first zone. This would mean
that your body is noticing that the
blood is too dilute. And if it's on this
side, your body's noticing that it's too salty. The body is saying that
the blood is too salty. And so in this
case, if you have, let's say-- like I
said-- a meter down here, if the needle is
falling in this area, then that's going to be a
trigger for ADH release. So that's the first trigger
that we can talk about. In fact, why don't
I even go back up and add that to our diagram? So I'm going to put
that into our diagram so that we can see
it very clearly as being one of the triggers. So let's imagine you have
right here a little nerve cell. And I'm going to draw it this
way purposefully because we actually don't know where
these little osmoreceptors are. All we know is that
they do a fantastic job, but we don't know exactly
where these osmoreceptors are. And this is my little
diagram that I drew before. And you can now think, if the
osmoreceptor is telling you that it's over there,
then that's a problem. And in fact, why I don't
I even go one step further and label this as
my osmoreceptor? So if my osmoreceptor is set
to tell me that it's too salty, that is one of
the signals that's going to trigger ADH release. OK. So now, what's the
second trigger? What's another reason
why we might release ADH? Low blood volume. Think about that for a second. How in the world would
your body even know that the blood
volume is too low? Well, let's go back to basics. Let's go back to the heart. That's where I like to
begin because that's how I always think about it. Just very simply, what
is going into the heart, and what's coming out? Well, we know we have
blood vessels-- large ones, in fact, large veins--
dumping into the heart. So we have the superior
and inferior vena cava. This is the superior vena
cava-- this is a large vein-- and this is the
inferior vena cava. These aren't the
only large veins, but these are two
examples of large veins. And we also have
the right atrium. So we have a couple
of spots here that are in the
blood vessels where we might have little
nerve endings. So nerve endings
in these areas are going to start recognizing
when the blood volume is low. Because, remember,
the venous system-- this is kind of a stretch-- the
venous stretch from something we talked about a long time ago. The venous system
is actually going to be a large volume system. So if there's ever a
decrease in the volume, that would be one of the
best places to figure it out. So information in the walls-- so
basically, these nerve fibers, rather, in the
walls of the vessels are going to be less stretched. And they're going to say, well,
why are we less stretched? And the answer is that there's
actually less blood volume. So when they're less stretched,
they're going to send a signal and say, hey, something's up. We have less blood
volume, and I think the brain needs to
know about that. So that's how a signal gets sent
all the way up to the brain. And actually, I can
draw that in as well. So let's put in a
little receptor here. And now, these are going to
go down and sense low volume from those receptors
in the large veins and the right atrium. OK. Now, what's another trigger? You can see there are a
lot of different triggers. I'm putting up
one after another. Let's put another
trigger up there. What's another reason why
ADH would be secreted? Well, maybe a decrease
in blood pressure. Now, we know that
the veins tell us a lot of information
about volume. So it might extend that
the arteries can tell us about pressure. And you might recall
from another video where we talked about
baroreceptors that this is a fantastic way to get
information about pressure. So let me draw some of
those baroreceptors. And baroreceptor just
refers to pressure receptor. We have baroreceptors that are
in the aortic arch right there. And we also have
baroreceptors that are in the carotid
sinuses on both sides. So these baroreceptors are going
to recognize when the blood pressure is starting to go low. And they're going
to send a signal up to the brain to
say, hey, again, we need to do something about this. Our pressure is low. So that's another
signal up to the brain. And that we can
draw it right here. We could say, OK. Maybe something like this. And that would be a
signal about low-- let's write that
here-- low pressure. So now we've got signals about
high osmolarity, low volume, low pressure. Are there any other signals
that we can think of? One more jumps to my
mind-- angiotensin 2. Remember, angiotensin
2 is actually part of the whole RAS system--
the renin-angiotensin-- or I'll just write AT--
aldosterone system. And so angiotensin 2 is actually
going to be another trigger. So you can actually imagine
through a blood vessel, and you might have
a nerve nearby. And this is going to trigger
right here this molecule of angiotensin, which has
eight little amino acids. It's going to be a
signal to that nerve that it needs to let the body
know-- or the brain know, rather, that pressures are low. This is another signal. And let me just write that
up here in our picture. Another signal could
be something like this. Maybe right here. And the exact location
that I'm drawing is actually just
kind of arbitrary, but the idea is that
you have angiotensin 2 having effects on
the brain as well. So this little molecule
is going to come and let the brain know that, hey,
even the kidneys are trying to do something about
the blood pressure. And it would be great if
the brain got involved in releasing some
ADH, if needed. So these are the
different triggers. And like I said
in the beginning, probably the main one
you want to think about-- as far as ADH is concerned--
is this osmoreceptor. This is really the
most important one because everything else
is secondary to that. That is definitely the
major function of ADH.
