00:00
In order for you to approach this graph,
a different twist complicated? No,
it is not. If you have understood everything
I said, you will be good here. Or what you are
going to do ladies and gentleman is pay
attention to what I am saying and only after
I give you the priority, then on your own
time, you are going to move through another
point. You will see what I am talking about.
So stick with me very closely. Here we
have the X-axis. The X-axis represents plasma
osmolality. The reason that I am emphasizing
plasma is because as students talk about osmolality
and the boards in the wards, everyone expects it to
be lowered at all times and so, therefore,
whatever that comes out of your mouth must
represent or reflect what you are actually
thinking right? So that osmolality, two major
compartments, urine, plasma.
You always pay attention to
the adjective of that osmolarity. Here it
is plasma. Are you clear? With the plasma
osmolality, let us say they we are approximate
280. That green line in the middle that you
see there then represents your normal ADH
release. Once again you tell me who is the
most important regulator of your plasma osmolality.
Is it ADH or aldosterone? Good. It is ADH.
01:21
So as you move up the X-axis, 280, 290, 300,
310. I am not going as far as 310, let's go
about 300, you will notice that there is a linear
increase in plasma ADH release, as it should
be. Now take a look at this. Why in the world
did your ADH release so significantly increase
when you had only little bit of change in
plasma osmolality? This is the red line and
this is the most important point that you
want to take out of this. Once you have understood
this, I am not going to cover that 10 percent
decrease in volume. I will, however, talk
about the 10 percent decrease of volume and
pressure and as to what kind of effect it
then has on ADH. If you are going to lose
greater than 10 percent of your volume, what
does this mean to you? Massive hemorrhage
who have hypovolemic shock, do we not? You
are going to have a crossover effect in which
you have angiotensin II which is also going
to stimulate the posterior pituitary to release
ADH. So now what ends up happening? Even at
low levels of plasma osmolarity at 270. Let
us say that the lower normal limit is 275,
and even before we begin, listen, say that you
have low plasma osmolarity, what should normally
be your ADH release? Take a look at the normal,
the green line come all the way to the bottom
come to about less than 280. You start coming less
than 280, where are you? You are at zero.
02:56
So that would mean that if you are less than
280, you should not be releasing any ADH.
03:01
Correct? So why in the world at 270, you have
such a spike. Take a look at the red line.
03:08
Why there was such a spike in ADH? Because
a massive loss of volume, and this would then
as I said, the volume takes precedence over
the osmolarity even though it is decreased
so that you can raise their blood pressure.
Once you have understood that, you can then
move on. If you want, you may then take a
look at the other side here where we have
a 10 percent increase, but at this point,
it is much more important that you pay attention
to the red line. Significant, the hypothalamic
osmostat is reset by large changes in volume,
by large change we mean greater than 10 percent.
For example, hypovolemia. A given plasma osmolality,
let us say at 270, will result in a much
higher ADH. Take a look at 270. Let us say
about 275 right there. Move up the Y-axis.
You see then the red line that is because
of massive hemorrhage, ADH is in there. ADH
is absolutely increased so that it can restore
the blood pressure. ADH levels will be titrated
to achieve a lower plasma osmolality and that
will actually be the goal to replenish your
blood pressure. A lot of information there.
04:19
Good stuff. Detailed, just enough where you
can get every question right. It is just enough
so that it has you thinking so you put in the
physio and the pathology and you are able
to properly manage your patient and know what
the heck is going on when you get labs and
require to properly interpret. Let us now
move on.