Regulation of blood pressure with baroreceptors | NCLEX-RN | Khan Academy
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Regulation of blood pressure with baroreceptors | NCLEX-RN | Khan Academy

September 2, 2019

Let’s talk about blood
pressure homeostasis. And what homeostasis
means is balance. So how is it that our body
is able to create balance for our blood pressure? So this is the
heart, and we’ve got branches of the aorta
coming off of it. I haven’t been drawing these
branches every single time, but this time I think
it’s quite helpful to see. We’ve got here the
left brachial artery, going out to the
left arm, and we’ve got the left
carotid artery here. And again, I’m
writing left and right from the perspective of the
person whose heart this is. And you’ve got here the
right carotid artery and the right brachial artery. So this is blood going
to the right arm. And we’ve got blood
going to the right neck. One interesting thing, if you
look at the right carotid, is that it bulges right
here- in fact, both sides do. And they bulge right
before they split. And so that bulge is actually
called the carotid sinus, right here. And we call it that because
a sinus is any cavity. And so this is the
right carotid sinus, and this is the
left carotid sinus. Another spot I’m going to
talk about in this video is the aortic arch,
which is right there. So these three spots–
the two carotid sinuses and the aortic arch– are
really, really, interesting, and actually they’re very
important for learning about how it is that our body
is able to create balance in our blood pressure. So at the top I drew
kind of a blow-up version of the carotid sinus, and at
the bottom is the aortic arch. And if you look closely
under a microscope, you’d see nerve endings on
the outer layer of the vessel. And so these nerve
endings basically join up and form a nerve, and
these on the carotid sinus do the same thing. And they are basically
going to form two large nerves that go off. And they send
information about what’s happening in the blood vessel,
specifically about stretch. So as blood is pulsing
through this vessel right here, this carotid sinus, or as
it’s pulsing through the aorta, even, that wall is
being stretched out. And as it gets stretched
out, these nerves– they’re very special nerves, they’re
called baroreceptors. Baro, meaning pressure, and
they’re receptors for pressure, so they’re baroreceptors. These baroreceptors are
feeling the effects of stretch. And what they do is,
they send a signal down the nerve that
tells the brain how much stretch is happening. And so if this is the brain,
let’s say, we have here your midbrain,
these nerve endings are going to actually
go here, and tell the brain–
communicate information about how much stretch is
happening in those vessels. Now we know that the more
pressure is in the vessel, the more it’s going to stretch. So follow with me
in a little example. So let’s say we have
blood pressure here, and let’s say I have my blood
pressure of 115 over 75. And in green, I’ll write
action potentials per minute. So what happens is that as my
blood pressure is 115 over 75, those nerves are feeling a
certain amount of stretch, whatever that amount is, and
they’re going to send a signal. Not just one, but they’re
going to send a handful. So let’s say they
send 10 signals. 10 signals. I’m going to draw them out here. 5, 6, let’s say 7, 8, 9, and 10. 10 in one minute. And actually, let’s just
imagine that both nerves are doing this. So they’re doing 10 per minute. Well, that’s a pretty
normal number, let’s say. And this, over
time, becomes what the brain regards as
my normal set point. The brain starts to assume that
if 10 action potentials are fired per minute, then
that’s pretty normal for me. So it regards this as
my normal set point. Now if my pressure
goes up– let’s say that I’m running
late to an exam, or something happens
that really worries me, and my pressure
goes to 140 over 90. Now I have hypertension. And this is my new pressure. This would be much
higher than normal. So my body would register
this and my nerves would start firing, let’s
say at 30 times per minute. So if they’re firing
at 30 times per minute, then my body is
thinking, or my brain is thinking, well, that’s
higher than normal. So this must be high. It regards this as high. And on the flip side,
let’s say that, you know, I have– let’s say I cut my
arm and I lose a lot of blood, and my blood pressure
starts to fall. My stretching is going to
happen less than before. So it’s going to send less
action potentials per minute, maybe only seven per minute. And again, my midbrain
is going to get seven little green arrows
per minute, seven action potentials per minute. And it’s going to think,
well, that’s very odd. Before, it was 10 per minute. So this represents a
fall in blood pressure. So now you have high
blood pressure in pink, and a fall in blood
pressure in blue. So what exactly
can the brain do? What can the brain do to help
normalize or create balance? So let me write that
in red over here. Let’s write response,
question mark. So the body has a
couple of strategies, and they’re basically
summed up in the autonomic nervous system. And there’s two major branches
of your autonomic nervous system, or two parts
to it, let’s say parts. One is called the sympathetics,
almost like sympathy. And the other is called
parasympathetics. They’re very similar
words, except the word para is in front of this one. And I want you to remember
now that there’s a formula. And I’m going to write
that formula down here, just to remind us that pressure
equals flow times resistance. And additionally, I
want you to remember that flow– this
one right here– is going to be related to
stroke volume times heart rate. So if I can do anything–
if my body can do anything to raise a stroke volume or the
heart rate, or the resistance– then my pressure will go up. And vice versa, if I can drop
the stroke volume, or heart rate, or resistance, then
my pressure will go down. So what the
sympathetics do is they have an effect on the
heart and the vessel. And these blood vessels
are all over the body, not just the carotid
sinus or the aortic arch, I’m talking about
all blood vessels. And so the sympathetics are
going to, for the heart, they’re going to
increase the heart rate. And they’re going to
increase the stroke volume. And the parasympathetics
do the opposite. They actually drop
the heart rate and drop the stroke volume. And the way that they do that–
the heart rate is controlled by how many beats
you get per minute. Obviously, that’s
the heart rate. And the sympathetics are going
to cause the heart cells that control that to work faster,
and the parasympathetics will slow them down. And for the stroke
volume, the sympathetics force the heart to
contract harder. And then you have more
volume of blood gushing out with every beat. And the parasympathetics make
the heart work less forcefully, so you have less blood
gushing out with every beat. And the sympathetics–
finally, they actually cause vasoconstriction. And, you guessed it,
the parasympathetics do the opposite. So they cause vasodilation. And vasoconstriction and
vasodilation basically mean whether the artery
stays open or closes down. So for the sympathetics,
the arteries and arterioles, primarily, mostly
it’s the arterioles, they start to get smaller. And as they get smaller,
that increases resistance. And for the
parasympathetics, they will cause the arterioles
to get bigger, to dilate. And that will cause
the resistance to fall. So taking a quick
peek at our equation that I wrote out for
you on the right, you can see that the
sympathetics basically do everything that will help
to increase the pressure. So if you have a pressure,
again, of 140 over 90, then what will
happen is your body will see that as a
high pressure and will try to get the
parasympathetics to be active– will activate all the
parasympathetic nerves. And if your pressure is
low, if it’s 90 over 60, then the body is
going to respond by getting all the
sympathetics to react. You see how that works? And of course, if your pressure,
let’s say, is 115 over 75, and the baroreceptors
are firing, you know, the usual
10 times per minute, then there should be
really overall no response. So here you would
really get no response, because the body is
thinking, well everything is already balanced, there’s
nothing for it to do. So this is how the
body is able to control blood pressure in a rapid way. So that’s the final
point I want to make. That the input here,
the baroreceptors, these are nerves. And the autonomic nervous
system, obviously these are nerves. So the information going
in, is the baroreceptors. The information going out is
the autonomic nervous system, and all of this is
happening rapidly. This is all very rapid. And when I say rapid, I mean
on the order of kind of seconds to minutes. So within seconds to minutes,
this response can happen. So this is a fantastic
example of how your body can take in
information really quickly, and really respond quickly to
help keep your blood pressure balanced.

Only registered users can comment.

  1. Is it true that parasympathetic do not play a role in vasodilation; rather vasodilation is due to inhibition of sympathetic via inhibition of cardiac-activating center and/or vasomotor centers?

  2. Thanks Rishi. I am a first year med student in Australia. Your videos make tricky concepts super easy to understand. Please keep it up. You're awesome.

  3. Great video as usual, one question. I thought that the ventricles only had sympathetic innervation, if that is true how does a parasympathetic response effect stroke volume?


  4. My teachers stressed today that the parasympathetic NS only affects the heart frequency, not the contractility. Is that correct?

  5. There is no left brachiocephalic artery, and on the right it's the brachiocephalic trunk which branches into the right common carotid and the right subclavian. There's a lot of mistakes in this…be careful.

  6. Thank you so much, my friend introduced me to your videos when i was in high school and now i'm in university still using your videos. they are so helpful and i hate to admit this but they are perfect for last minute studies cause they just summarise everything so perfectly. you are honestly a life saver! I tutor kids as well, so i always show them your videos and share these <3 keep doing what you are doing, these videos are amazing

  7. It still surprise me, just how some people don't know about Hibloderox Remedy (just google it), although many people completely cure their hypertension naturally with this remedy. Thanks to my work buddy who told me about Hibloderox Remedy, I finally eliminated my pain & embarrassment for good with natural ways.

  8. Maybe be more careful with your drawings? (Even though I know it's just a sketch) The aorta originates on the left part of the heart. You forgot to mention the Truncus brachiochephalicus. The Brachial-Artery is not a branch of the Aorta, the branch you mistakenly named A. brachialis is the A. subclavia.

  9. Also believe that the parasympathetic nervous system provides no innervation to blood vessels. So less sympathetic activity will dilate the vessels and lose some of its tone. Likewise an increase in sympathetic activity will increase the tone and cause vasoconstriction. Good Video to clear out the cobwebs though. 

  10. This video is awesome .. but there is something wrong .. The parasympathetic NS Doesn't have a role in Blood vessels dilation ! instead, what causes vasodilation is the INHIBITION of the sympathetic NS.. isn't it?
    Thanks a lot 🙂

  11. There are several important inaccuracies in this twelve minutes including the parasympathetic dilation and the fact that the brain area is primarily the brainstem not the "midbrain". This reflex arc changes heart rate on a beat to beat basis so that baroreceptors firing 20 or 30 times per minute would be useless – the actual number is closer to 50 action potentials per second. Sadly the facts are lost on the general public as long as it seems correct. The number of folks congratulating this video for its "knowledge" speaks loudly of quality control. Really a pity that this is what passes for education.

  12. why do you have the glossopharyngeal and vagus nerve going to the mid-brain when it goes to the medulla oblongata please? coz it's confusing me, thanks 🙂

  13. Greatest video!  First of all, your voice is always so enthusastic that it is a pleasure to listen to all of your videos.  And second of all, I could never figure out exactly what they were talking about when books mention, but do not really explain baroreceptors.  I LOVE how you related everything to the formula–now vasoconstriction, dilation, and the action of aortic and carotid  bodies makes TOTAL SENSE.  THANK YOU!!!

  14. Got a question if baroreceptors not doing their job for whatever reason , is there any way they can be manuplate to comply, this is one of the reason with Parkinson , MS and maybe alzheimer desease,  Maybe angioplasty ! 

  15. Carotid sinus is actually a dillatation of the internal carotid artery (superior to the bifurcatio). Nice video tho. 🙂

  16. hey just wanted to say a huge thank you for the tutorials you've put up . Theyve been a massive help in grasping all the concepts.

  17. I wish that you were my physiology teacher 🙂 Thank you very very much. I understood the issue completely. My lecture notes did not help me like you about this cardio-vascular system 😀

  18. Vagus nerve does not end up in the midbrain, nor does glossopharyngeus nerve. Parasympathetics doesn't make blood vessels dilate. If the pressure is high the vasomotor center inhibits sympathetic system. Despite those the other parts are great. Thank you for illustrating and making things that we read easier to understand.

  19. shouldn't this be the L. Subclavian and Brachiocephalic artery when talking abt the arches… otherwise great video

  20. Such a helpful video, never fails to broaden my understanding of topics i thought i would never get or had little knowledge on.. Great for exam prep!

  21. parasympathetic can decrease the Stroke Volume? according to what i have been told, it is only sympathetic devision can actually decrease or increase the stroke volume!

  22. Great teachings, but if you can use legit markings in terms of numbers (ex. the amount of Action Potentials transmitted) instead of a random estimation that would really help out.
    Thank you for your consideration.

  23. I think you mistook subclavian artery for brachial. Brachial artery is a branch of axillary artery which is a branch of subclavian

  24. The brachiocephalic artery is the first branch on the ascending aorta, not the right subclavian and the righr common carotid. Although they branch from the brachiocephalic artery, it is important to clarify that arterial trunk.

  25. Thank you so much for this demo. I am studying Paramedical Science and this was spot on! This really helped me understand Baroreceptors in maintaining BP. Thanks heaps!

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  27. Hey, thanks for the video – I did notice an error around the 9:30 mark. Sympathetic increases HR, SV & TPR. However, parasympathetics only have an effect on decreasing HR (their effect on decreasing SV is indirect, and they do not affect TPR at all). Wanted to point this out as it is important to understand! Cheers

  28. RIGHT AND LEFT SUBCALVIAN ARTERY, the left comes directly from the arch or aorta and the right arise from the barachiocephalic artery 🙂

  29. Vasodilation is caused by a lower action potention of the SNS not the PNS. When vasodilation is needed in order to reduce resistance such as when BP is high, the SNS begins to send less signals, thus begining to relax the smooth muscles of the arterioles (tunica media). This is turn makes the lumen wider (dilated) leading to reduced resistance and hopefully a decrease in blood pressure (BP). Great video, very easy to understand

  30. u said sympathetics increase the blood flow in not just the heart but all over the body(.but it does not increase the blood flow to cerebrum ) except it This is awesome video.

  31. Followed most of the recommendations in this blood pressure level solution “Zοtοsο yuku” (Google it) for 30 days and a half. I am obese, diabetic person with Stage II Diabetes, and also have high blood pressure. I needed to pass the exam for D.O.T. Physical. I lost Thirteen lbs, my Blood pressure went from average of 155 to 136. I keep an eye on my blood sugar levels and it is now 125-130 when compared to the last time which was always somewhere in the 160s.

  32. pls enlighten me. If we say an indvidual exercises, and to maintain homeostasis, the peripheral and central chemoreceptors send signals to the medullar oblongata, and then it sends nerve impulses to the effectors to increase exhalationa and inhalation. With regards to the cardiovascular system, it increases the blood pressure to increase the rate of flow of oxygen throughout the body. Is this a positive or negative feed back? Cus i know that there are only 3 or 4 types of positive feedbacks and this is not oe of it. If it is negative how so> Because it looks like the the response is magnified with the continous stimulus. Pls explain. Thanks.

  33. Cheers for the video content! Apologies for butting in, I would appreciate your opinion. Have you researched – Marnaavid Unexplainable Intervention (Have a quick look on google cant remember the place now)? It is an awesome one of a kind product for learning how to hack your flow state minus the normal expense. Ive heard some interesting things about it and my work buddy at very last got astronomical results with it.

  34. The video describes two arteries, left and right brachial arteries, they aren’t. They are the left and right subclavian arteries. The brachial arteries are in the arms.
    Can’t comment on the rest of the video as I stoped watching at this point. IMO, if they get this very basic anatomy wrong I can’t trust it a simple a revision source for my imminent exams.

  35. There are many systems for regulation this only explains the baroreceptor reflex it would be nice if u explain the other systems as well…😁

  36. We just learned about regulation of arterial pressure today. Our professor teaches from the BRS textbook. He told us that the parasympathetic autonomic nervous system does not affect blood vessels (i.e. arteries and veins), it only affects the heart. However Dr. Desai pointed out it does (10:12). Please help me out here… I am confused as to which one holds credible 🙁

  37. I think you also need to explain how this regulation mechanism relates to RAAS. Otherwise one might get the impression that the brain is the sole regulator of blood pressure, which obviously is not the case.

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