and these are the wheels that we shall
see. Now, let me explain the wheels to you because
these are beautifully done, well color coordinated
and the way that it has an influence on each
other. You should have these wheels permanently
etched in your head, one in one eye, the other
in the other eye. Now, towards normal,
let us talk about tonicity, ADH, and excretion
or retention. I do want you to pay attention
to the colors. Okay. So let us begin on the
area of osmolarity first. So we are going
to take a look at the right circle first.
You find that the tonicity is increased. I
want you to follow the red arrow, and what is
in red only, at this juncture. How does that occur?
Maybe they were sweating. What sweating mean
to you? It is hypertonic loss of sodium,
meaning you are losing more
water than you are of your sodium. Thus,
your plasma osmolarity increases. That we
have talked about. Once the plasma osmolarity
increases, immediately from the posterior pituitary,
you are going to then release your ADH, of
course, coming from the hypothalamus. Then
what does this ADH do? I want you to go up
to water, in red. You know that ADH is going
to retain water. In other words, you are going
to reabsorb water from the collecting duct
technically. Doesn't it? In the hopes of doing
what to tonicity? Bring it back to normal.
Are we okay?
Let us take a look at the other example. What
if your tonicity is decreased? Simple example
such as drinking water. You drink water,
excess. What happens to plasma osmolarity?
You are drinking pure water. So all that you
are doing is strictly increasing
the total body water in the denominator. If
that is happening, then you know that your
plasma osmolarity is decreased. All I am doing
here is integration of the topics that we
talked about with the ratio. How do you
determine plasma osmolarity? Serum sodium.
What does serum sodium mean to you clinically?
It is the total body sodium over total body
water. Our discussion with that, we talked
about in great lengths. If that is not clear
and you cannot recall that I would once again
recommend. You go back and take a look at
the lecture series. So your plasma osmolarity
is decreased because of, well let us say excess
water. Thus, what are you going to do with
ADH? Suppress the release of it. Suppress
the release, why? Well because you have too
much water consumption. Don't you want to
urinate this out? Of course, you do. So why
don't we suppress our ADH? So now by suppressing
ADH, in blue, what are you going to do with
that water? Excrete it. You tell me what kind
of urine you are producing? What kind of urine?
Dilute or concentrated urine? Good. Diluted
urine. So that you can bring the tonicity back
up to normal. You see how important it is.
That is happening in us right now. Let us
go over to the left. On the left, here we
will be dealing with you begin with effective
circulating volume. Let us go with the one
in the red again. Say that you are losing
effective circulating volume, what does that
mean? Plasma. So what are you going to release?
I want you to go down to the kidney. If you
have decreased perfusion to the kidney, you're releasing
renin and company. I want you to focus upon
aldosterone. What is that aldosterone going
to do in the collecting duct? Please go to
red. The red saying sodium reabsorption. When
you have sodium reabsorption, what are you
doing to volume? You are then going to increase
the volume back towards the normal. Are we
clear? What if you increase your effecitve
circulating volume because maybe perhaps you
infused too much normal saline? You will infuse
too much normal saline, increased effective
circulating volume, what then happens to your
perfusion to the kidney? Increased. What are
you going to do with renin? You are going to suppress
the release of renin. So, therefore, what
are you going to do with sodium? You are going
to excrete the sodium so that you can bring
your volume back to normal. Interesting. Sodium,
volume left circle regulated by aldosterone.
On the right, water tonicity, regulated by ADH.
Do you see anycross over here? No. In the previous
statement, in the previous discussion, I brought
the term or introduced the term crossover
to you, we're not seeing it here yet. Here we
go. So the crossover has taken place. So what
does this even mean? At all times, it is imperative
and of at most priority that you maintain
plasma osmolarity within normal range. There
is always an exception. Here it is. Say that
you get into an accident unfortunately and
you are losing tonnes of blood, massive hemorrhage.
You are losing so much hemorrhage that it
is 10 percent of or greater than 10 percent
effective circulating volume, which is depleted.
The volume has been lost so much. It is now
the body's responsibility to now increase
the blood pressure as quickly as possible
as dramatically and desperate as possible.
It is desperate right.
So, therefore, aldosterone is being
kicked in, and that out the sodium, you
try to retain the fluid maybe perhaps that
is not enough. You bring your angiotensin II
from your left circle with enough volume
loss. You are going to stimulate ADH in the
hopes of doing what? To then retain and reabsorb
that water so that you can bring blood pressure
back to normal.
My recommendation for you to learn this is
first you take a look at the circles seperately.
You go in the priority order that I had
given you with organisation, which is tonicity
first, then volume. Number 2, right circle, left
circle. Once you’ve firmly implanted those
circles in your head, then you move over
to crossover, understand when that takes place
that will be massive hemorrhage when you are
losing greater than 10 percent of your effective
circulating volume. What then takes priorty? The volume
takes priority over osmolarity at this juncture.