Circumventricular Organs (CVO's) and Cerebral Spinal Fluid

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.