Okay, welcome back. We are going to learn again one very important concept which is the regulation of blood pressure. So
what are we talking about? Every person has a set blood pressure. So
for instance, if my blood pressure is 110 by 70 this is the systolic number and
the diastolic number. This is what my systems are programmed to function with.
If there is any increase or decrease in this set homeostatic number they are
going there are going to be mechanisms in our body that will start to work in
order to restore the homeostatic number. So we’re going to look at some
short-term mechanisms and what do we mean by short-term? These will work very
quickly. So the response to the change in blood pressure will take from seconds to
minutes. We’re going to talk about the baroreceptor reflex, the
chemoreceptor, some hormones: EPI, Norepi, APA, ANP and ADH. A little longer term, the RAA system. Will just take a little longer. So these will respond first and if still there is change in blood pressure this will be
activated. All right, in order to understand how blood
pressure works or who controls the heart and the blood vessels we’re going to go
back and look at the numeral control of those organs. So within the medulla
oblongata of the brain we have the cardio vascular center. It controls the
heart and the blood vessels. If you see this is two parts of the word. Cardio because we are going to look at the cardiac center. Vascular we’re going to look
at vasomotor center of the blood vessel.
So, the Cardiac Center first. What does it do? It is going to carry nerve
impulses to the heart. One branch is the sympathetic. So if there is sympathetic
activity from the medulla to the heart this will increase the heart rate,
increase the force of contraction of the ventricles. If there is parasympathetic
stimulation it will do the exact opposite. It will inhibit, the heart. So this
is the first part of the cardio vascular center. The second part is the vasomotor.
So this is the autonomic control of the diameter of the blood vessels. Again it’s in the medulla oblongata and it’s going to take nervous impulses towards the
blood vessels. If we stimulate the visual motor center, we will have sympathetic
stimulation and vasoconstriction. If we inhibit the visual motor center we will
end up with vasodilation. This is a combined effect. So just for you to
remember, this is the medulla oblongata where I have the cardiovascular center.
Some of the impulses will go to the heart and some will go to the blood
vessels. So how does the medulla oblongata know which type of impulses to
send? It has to receive information from other areas. And this is where we’re
going to talk about some of those receptors that will detect changes in
blood pressure and accordingly they will send information to the medulla and the
medulla is going to send the proper input towards the heart and
the blood vessels. This is a nice differentiation between the sympathetic
and the parasympathetic activity that comes from the cardiovascular center. I
want you to review this and study it very carefully. I’m just going to point
to the outcome. If there is sympathetic activity, I will have increase in the
cardiac output and increase in the blood pressure. If on the other hand, the
parasympathetic activity takes over, the exact opposite, the outcome will be
decrease in the cardiac output and decrease in the blood pressure. All right,
let’s start talking about those detectors we were talking about. So we’re
going to start here. We’re going to follow those receptors. We’re going to
start with the baroreceptor reflex. Now we’re talking about baroreceptors.
What do we mean by baroreceptors? Baro means pressure so I’m talking about a
pressure receptor that is going to detect changes in blood pressure. Where
are they located? These are my baro receptors in the aortic arch. These are
baroreceptors in the carotid sinus. Every time the ventricle contracts and
pushes blood out there’s going to be stretch on the wall of those vessels and
the baroreceptors are detecting. Is this pressure normal? Is it higher? Is it
lower? So baroreceptors are located in the carotid sinus and the aortic arch.
What are they going to do? Baro receptors are going to start a reflex if
there is abnormal blood pressure. What do I mean by reflex? Receptors will send
neural information to medulla oblongata and the medulla is
going to send information back to the heart and the blood vessels. I call this
a reflex. So, change in blood pressure detected by bottle receptors will go to
the medulla oblongata and the medulla will send information back to the heart
and blood pressure to change those parameters. This is what we call a reflex.
It’s a very fast neural circuit. It takes seconds. It is automatic. It is always
predicted. Every time a change occurs the outcome is going to be exactly the same.
So, let’s look at the example of how the baroreceptor works. So this is my
homeostatic normal range of blood pressure. If the blood pressure decreases,
immediately the baroreceptors are going to sense this change. They are
going to send information to the medulla oblongata. Medulla oblongata is going to
stimulate the sympathetic branch of the autonomic nervous system. This will
increase the heart rate contractility of the ventricle. This will increase the
cardiac output. It will send sympathetic stimulation to the vasomotor center,
constrict the blood vessels. Those two effects together will increase cardiac
output and resistance and will restore the blood pressure back to its normal
levels. And remember, the exact opposite. So the baroreceptor reflex will respond
to either increase in blood pressure or decrease in blood pressure and these are
exactly the steps and they will be reverse. So that the outcome here if I
have an increase in blood pressure all of those steps will restore the blood
pressure back to its norm. If I have low blood pressure all of those steps will
increase the blood pressure. Restore it back to its norm. All right. Done with the
baroreceptors. We’re going to look at chemoreceptors. From the name, what do I
mean by chemoreceptors? These are receptors that are responding to
chemical changes in the blood. So what are the most important chemicals in the
blood? The level of oxygen. The level of carbon dioxide and the pH of the blood.
Any normal person we know will have high levels of oxygen, low levels of carbon
dioxide and the normal pH that is not acidotic.
So let’s look over here. Where do we find those chemo receptors? We’re going to
find some again very close to where the baroreceptors were. So I have the aortic
bodies in the wall of the aorta. I have the carotid bodies in the carotid
arteries over here. So these are chemo receptors and because they’re in the
heart we call them peripheral chemoreceptors. They will monitor the
level of oxygen, carbon dioxide and the pH of the blood. But I also have another
chemoreceptor. When the blood reaches the brain it’s going to be filtered as
cerebrospinal fluid and there is a chemo receptor in the brain in the medulla
that is going to check the cerebrospinal fluid. And if there is any change in the
pH this is my central chemoreceptor because it is in this center
nervous system. It will respond again to this change in the pH. Alright, so we know
where the chemoreceptors are. Now what do they do? We are going to look at them
again. They will initiate a chemoreceptor reflex. I have my receptors. They’re going
to send very quick information to the medulla. The medulla is going to affect
again the blood vessels and the heart. We learned what we mean by a reflex. I want
you to look at those changes. These are three changes that occur together at the
same time. Anytime there is a lowered blood oxygen in the blood there’s going
to be increased carbon dioxide. There is going to be low pH or acidosis. So if
this happens, decreased parasympathetic effect on the heart will increase the
heart rate. Increase in parasympathetic in the heart will increase the heart rate and
the stroke volume. Sympathetic stimulation of my vasomotor center
will vasoconstrict the blood vessels. So, this is the outcome of increase. The
heart rate, stroke volume, vasoconstriction. So what am I really
doing? Increasing heart rate and stroke volume, cardiac output. I am moving blood
quicker away from the heart to the lungs and to the tissues because this is where
it can pick up oxygen and get rid of the excess carbon dioxide. And this will
bring those parameters back to normal. So these are my chemo receptors they will
do the effects we just mentioned and this is the final result. They will speed
the return of the blood to the heart and to the lungs so we can pick up oxygen
and get rid of carbon dioxide. The third parameter we’re going to talk
about is the effect of hormones on cardiac output. So the first one is
epinephrine and norepinephrine. These are produced by the adrenal gland. The
adrenal gland is the little gland on top of the kidney. And when we look at the
central part or the core part we call this is the adrenal medulla. And the adrenal
medulla secretes the two very important hormones, epinephrine and norepinephrine.
When are these produced? Every time there is sympathetic stimulation to the brain
and the nerves information is going to travel very quickly to the adrenal
medulla and it will increase its secretion of those two hormones which
will increase the cardiac output exactly like the sympathetic simulation. Another
hormone is ANP, Atrial Natriuretic Peptide. So if I say atrial where does it
come from? From the atrium. How is it produced? The volume of blood that
reaches the atrium will stretch the atrium. So anytime there is increase in
the volume of blood in the atrium and I have excess stretch ANP is going to
be produced in large amount. What does it do? ANP goes to the kidneys because I
have high blood pressure or high blood volume and I want to get rid of this. Who
is the organ that can read get rid of excess fluid? The kidneys. And this is
exactly what the ANP is going to do. So we’re looking at here at ANP secreted by the atrium due to excess volume of fluid or high blood
pressure. This is going to go all the way to the kidneys and it will stimulate the
kidneys to lose sodium. Remember, every time sodium moves, water follows sodium.
So, there’s less reabsorption of sodium means we will excrete or lose the sodium
in the urine and sodium will pull the water out with it. So we get rid of this
excess blood volume. The blood pressure will decrease. So, I reverse this back to
the normal. I had high blood pressure, high blood volume, we have decreased it
back to the norm. Another effect of ANP is vasodilation and those two will
result in a negative feedback. I have restored the high blood pressure to its
normal level. Another hormone we’re going to talk about is called the anti
diuretic hormone or vasopressin. All right, let’s break this word into two
halves. Anti is against. Diuresis is loss of fluid in urine. So antidiuretic
hormone this hormone will prevent loss of water or urination. It’s produced by
the hypothalamus and stored in the posterior pituitary gland.
When is it released just as I told you if I have low blood pressure or low
blood volume this is going to be sensed by the hypothalamus and the pituitary
and high levels of ADH are going to be produced and they will conserve the
water restoring the blood pressure back to normal. And the exact opposite is true.
So we’re looking here. What’s my stimulus here? If I have low intake,
dehydration, the osmolarity of the blood will increase. The hypothalamus will
detect this by the means of Osmo receptors. It will stimulate the
posterior pituitary to produce higher levels of ADH.
These will go to the kidney, tell the kidney conserve the water, reabsorb it,
don’t lose it, I need the fluid. And this will increase
the blood pressure back and I will rehydrate my system. And this is the
exact opposite will occur if the circumstances were the opposite. All
right we said there is a short term that acts very quickly and as you can see
those different receptors and hormones will really act very quickly in the body.
But there is a longer term which means if there’s still abnormal blood pressure,
especially low blood pressure, and I need something more to be in effect we have
the RAA system. So what is the RAA system? It’s stands for all the names of
those hormones Renin-Angiotensin-Aldosterone. Who will
activate this system? If there is decreased in blood pressure or decreased
in blood volume. So let’s look what’s the first response
here? If I have low blood pressure and low blood volume, there is less blood
reaching the kidneys. Let’s learn this word, renal perfusion. Less blood flow
reaching the kidney. This is going to be sensed by very specialized cells in the
kidney called the juxtaglomerular cells. They secrete a substance called renin.
This is my first important hormone over here.
What does Renan do? Renin converts a substance called angiotensinogen into
angiotensin 1. What happens next? Angiotensin 1 will be converted into
angiotensin 2. I’ll take you through the rest of the story and then we’ll look at
this side. This is the series of events that I am following. Angiotensin 2 has
several effects. What is angiotensin going to do? Number
one, it’s going to go to all the arteries and cause vasoconstriction. Remember,
where is the problem? I have low blood pressure and low blood volume. What do I
want to do? I want to restore them back to normal.
So angiotensin 2 has direct effect on the arteries. It will cause severe
vasoconstriction. Actually, it is the strongest chemical in the body that
causes vasoconstriction. Where else does it go? It’s going to go to the adrenal
cortex. This adrenal gland has an outer area we call the adrenal cortex and it
will stimulate the adrenal cortex to produce a substance called aldosterone.
What does aldosterone do? It’s going to go to the kidneys and stimulate the kidneys
to conserve, reabsorb sodium. And if you remember, every time sodium moves, water follows sodium. So I am conserving water and sodium in the body. This will
increase the blood volume. This will increase the blood pressure. And we
restore the blood pressure back to normal . Now those two side steps here
just to explain what we’re looking at. angiotensinogen is produced in
the liver. So once I have Renan this is going to be secreted in the blood. When
the blood is traveling to the liver, it meets the angiotensinogen and it will
change it into angiotensin 1. And then blood again is circulating in my body.
When it reaches the lungs, there’s going to be a chemical substance here called
ace, or angiotensin converting enzyme and is will convert angiotensin 1 into
angiotensin 2. So this is just to tell you what are the sources of those
substances. All right, there is one more effect for angiotensin 2. We said the
first direct effect is going to be vasoconstriction of the arterioles. There
is an effect on the adrenal cortex. There is one more effect that we will see
clearly on this last slide. Angiotensin 2 stimulates aldosterone,
Arteriolar vasoconstriction.It will also increase ADH secretion by the posterior
pituitary gland which again will retain salt and water and increase the blood
pressure. And this concludes our discussion of cardiac output and thank
you very much.

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15 thoughts on “Regulation of Blood Pressure”

  1. omg thank you so much I've been searching all over internet for some information about what regulates the BP but nothing explains it clearly. Thanks ma'am!

  2. You guys only talked about arterial baroreceptors, but you didn't talk about low pressure baroreceptors. Could you please tell me what they do?

  3. Jesus! I’ve really struggled for years trying to understand this. Thank you so much. Been so worried about my exams, have one tomorrow! Now I can enter into the exam hall with my head held high. May God bless you ma!

  4. Very key-point concentrated, not like other lecture-talking all the time without pace and read whatever written down-anyone can do it. This is good presentation, can see Dr has multi-language skills and present this content in a logical and clear way. I really cant watch any video that presenter talk all the times without key point.

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