Where the brain gets its information and
where delivers various hormonal structures?
Where the brain gets its information
is via circumventricular organs.
Circumventricular organs are kind of think
about them as windows into the brain.
These are areas where you can either send some
information or you secrete a substance through.
And this will be important throughout the course and
when they come up will also bring them back into play.
So we will utilize this in different organ systems.
But our sensory circumventricular organs usually
involve this subfornical organ and the OVLT.
This are gonna be imported in the renal system
for helping us to control body osmolality.
We also have areas such as the area postrema that
will be involved with helping a sense or oxygen
and carbon dioxide concentration levels in
the respiratory component of the coursers.
Those secretory portions of the circumventricular organs
and these involves various secreting substances.
This will be important things, like
the pineal gland, this releases melatonin.
Melatonin is a hormone associated with these
circadian rhythms and you are release it more
certain times a day versus others.
We also have places like the median eminence
and the posterior pituitary.
We reutilize this in the endocrine section
because this are going to be areas in which
some of the hormones can live from.
Like from the posterior pituitary, its where
oxytocin antidiuretic hormone are released.
From the median eminence, we have all
the hypothalamic pituitary access hormones.
Now, where is the fluid that travels around
the brain coming from? And, how was that regulated?
Cerebral spinal fluid comes from choroid plexus.
This are located in the ventricles,
primarily the third ventricle of the brain
as well as in the fourth ventricle.
These are places in which, you are
going to be able to secrete fluid in to.
Then you can see it circulates around in the brain
and will eventually return to lymphatic system.
Its important to remember that the brain fluid is integral
to make sure that neurons survive and thrive.
But you can’t have too much of it around or what
will happen, the brain is encased in the skull.
Therefore, if you try to expand it, it is
going to start damaging those neural tissues.
So you have to make sure the pressure
stays low in the cerebral spinal fluid.
But this choroid plexus will be
making this fluid the whole time.
How does it do that? And what are its constituents?
Cerebral spinal fluid is made up of a little bit
higher sodium than what is located in the plasma.
Potassium levels are pretty similar, there
is less calcium, magnesium levels are similar,
higher amounts of chloride, a little bit
lower glucose, a lot lower protein.
And then pH is also lower.
So seeing this you wanna think to yourself, what are
some of the differences in cerebral spinal fluid?
Higher sodium, lower calcium, higher
chloride, lower protein and lower pH.
Those are the five big ones.
So lets talk through how cerebral spinal fluid
through the choroid plexus is produced
so that it has slightly different
constituents than water located in plasma.
That can probably best seeing at this type of diagram.
So let me orient you because this is going to be
a different picture than what we’ve seen some before.
You wanna think of the brain interstitial
fluid that is the fluid from the plasma.
You wanna think of the CSF which was the cerebral
spinal fluid that is what’s gonna base all those neurons.
Be located in the ventricles and so forth.
Different than many of the different endothelial
transport mechanisms, the sodium potassium ATPase
is located on the apical membrane
rather than in the basal lateral.
Almost all other tissues in the body
is located on the basal lateral line.
And that’s an important concept to keep in mind.
The other important things are what were
the ions we wanna to pay attention to.
We want to pay attention especially
the sodium, chloride and bicarbonate.
So let’s look at those three specifically.
Hopefully, you can appreciate it in a diagram
like this that bicarb is transport across
the apical membrane in high concentrations.
Is cotransported with both sodium and chloride.
This is telling you that you need
bicarb in the cerebral spinal fluid.
To be able to get bicarb there, you are going
to also transport a little bit more sodium and
a little bit more chloride.
And that is the reason why those are also
elevated in this cerebral spinal fluid.
So why you need the bicarb there?
Its because you don’t have any proteins.
Your protein level in cerebral
spinal fluid is really, really low.
And without proteins around you lose some of the
buffering capabilities that you have that in the blood.
Therefore, you need a higher amount
of bicarb in cerebral spinal fluid.
How do you get that extra bicarb?
You are going to have to breakdown C or
combined CO2 in water to carbonic acid.
Have that disassociate into
hydrogen ions and bicarb.
So of you are moving the bicarb across the apical
membrane, your gonna have to do something
with those hydrogen ions.
How do you do something with them?
You pump them across.
So you use these sodium hydrogen ionic
exchanger to get rid of the hydrogen ions.
That creates a little bit lower pH in
cerebral spinal fluid then what occurs
in the brain interstitial fluid and in the plasma.