00:00
Where the brain gets its information and
where delivers various hormonal structures?
Where the brain gets its information
is via circumventricular organs.
00:12
Circumventricular organs are kind of think
about them as windows into the brain.
00:17
These are areas where you can either send some
information or you secrete a substance through.
00:24
And this will be important throughout the course and
when they come up will also bring them back into play.
00:30
So we will utilize this in different organ systems.
00:35
But our sensory circumventricular organs usually
involve this subfornical organ and the OVLT.
00:43
This are gonna be imported in the renal system
for helping us to control body osmolality.
00:51
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.
01:03
Those secretory portions of the circumventricular organs
and these involves various secreting substances.
01:15
This will be important things, like
the pineal gland, this releases melatonin.
01:21
Melatonin is a hormone associated with these
circadian rhythms and you are release it more
certain times a day versus others.
01:30
We also have places like the median eminence
and the posterior pituitary.
01:35
We reutilize this in the endocrine section
because this are going to be areas in which
some of the hormones can live from.
01:42
Like from the posterior pituitary, its where
oxytocin antidiuretic hormone are released.
01:47
From the median eminence, we have all
the hypothalamic pituitary access hormones.
01:55
Now, where is the fluid that travels around
the brain coming from? And, how was that regulated?
Cerebral spinal fluid comes from choroid plexus.
02:07
This are located in the ventricles,
primarily the third ventricle of the brain
as well as in the fourth ventricle.
02:14
These are places in which, you are
going to be able to secrete fluid in to.
02:20
Then you can see it circulates around in the brain
and will eventually return to lymphatic system.
02:26
Its important to remember that the brain fluid is integral
to make sure that neurons survive and thrive.
02:35
But you can’t have too much of it around or what
will happen, the brain is encased in the skull.
02:44
Therefore, if you try to expand it, it is
going to start damaging those neural tissues.
02:49
So you have to make sure the pressure
stays low in the cerebral spinal fluid.
02:54
But this choroid plexus will be
making this fluid the whole time.
03:01
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.
03:14
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.
03:31
And then pH is also lower.
03:34
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.
03:48
Those are the five big ones.
03:50
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.
04:04
That can probably best seeing at this type of diagram.
04:07
So let me orient you because this is going to be
a different picture than what we’ve seen some before.
04:15
You wanna think of the brain interstitial
fluid that is the fluid from the plasma.
04:21
You wanna think of the CSF which was the cerebral
spinal fluid that is what’s gonna base all those neurons.
04:30
Be located in the ventricles and so forth.
04:33
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.
04:44
Almost all other tissues in the body
is located on the basal lateral line.
04:49
And that’s an important concept to keep in mind.
04:53
The other important things are what were
the ions we wanna to pay attention to.
04:58
We want to pay attention especially
the sodium, chloride and bicarbonate.
05:02
So let’s look at those three specifically.
05:06
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.
05:18
This is telling you that you need
bicarb in the cerebral spinal fluid.
05:22
To be able to get bicarb there, you are going
to also transport a little bit more sodium and
a little bit more chloride.
05:30
And that is the reason why those are also
elevated in this cerebral spinal fluid.
05:35
So why you need the bicarb there?
Its because you don’t have any proteins.
05:40
Your protein level in cerebral
spinal fluid is really, really low.
05:45
And without proteins around you lose some of the
buffering capabilities that you have that in the blood.
05:51
Therefore, you need a higher amount
of bicarb in cerebral spinal fluid.
05:55
How do you get that extra bicarb?
You are going to have to breakdown C or
combined CO2 in water to carbonic acid.
06:03
Have that disassociate into
hydrogen ions and bicarb.
06:07
So of you are moving the bicarb across the apical
membrane, your gonna have to do something
with those hydrogen ions.
06:16
How do you do something with them?
You pump them across.
06:19
So you use these sodium hydrogen ionic
exchanger to get rid of the hydrogen ions.
06:26
That creates a little bit lower pH in
cerebral spinal fluid then what occurs
in the brain interstitial fluid and in the plasma.