blood pressure regulation script
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Blood pressure regulation
Talking about CVS means that you have to talk about an important issue
which is Regulation of Blood Pressure
Previously weve discussed the systolic and diastolic blood
pressure;
#systolic blood pressure: refers to ventricular contraction
#diastolic blood pressure: refers to recoil of the aorta
# mean blood pressure:its the average blood pressure at a specific
moment; formula:
mean blood pressure =diastolic+(Systolic-diastolic)/3
Hypertension: it is the sustained elevation of blood pressurebeyond the normal average.
Now what is the relationship between Blood Pressure & blood flow??
Blood pressure: it is the force exerted by blood on a unit area of a
blood vessel.
Once there is an increase in the blood flow that will lead to an increase
in blood pressure and the blood flow is increased by an increase in the
hearts output rate which is related to the volume of blood pumped by
each ventricle per minute (not the total amount of blood pumped by the
heart)from Sherwood
Cardiac output = stroke volume * heart rate
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Once there is an increase in the stroke volume and heart rate, the
cardiac outputwill be increased thereby increasing the blood flowas
well.
Blood Pressure
#hypertension: increase in blood pressure.
#hypotension: decrease in blood pressure.
The fear of hypertension is due to the complications it may cause. Wedont care about hypotension which is within normal average especially
in ladies, they have hypotension (100/60) but it still acceptable.
However (80/30) is not acceptable.
Cardiac Output (CO) is the amount of blood pumped by eachventricle in one minute
CO is the product of heart rate (HR) and stroke volume (SV)CO = HR x SV
(ml/min) = (beats/min) x ml/beat
HR is the number of heart beats per minute SV is the amount of blood pumped out by a ventricle with each
beat
Cardiac reserve is the difference between resting and maximal CO
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Blood Pressure regulation
Blood pressure regulation is important and there are two mechanisms
for controlling it, we have short term regulation (moment to moment
regulation) and long term regulation.
1-Short termregulation:
it means the regulation of blood pressure within seconds, that is,
things that will affect the blood pressure in a short period of time like,
changing of the posture (position) of the human being, like sitting or
standing or lying down.
So it is the moment to moment regulation of blood pressure which isthe mechanism which takes care of the situation/position of the body.
However, long term regulation of blood pressure is over minutes and
above.
With short term regulation we talk about Baroreceptors.
Principle: in the arch of aortaand the carotid arterywe have
baroreceptors which are a collection of neurons which are sensitiveto either decrease or increase in blood pressure. It is closely
related to ohms law in blood pressure, which reflects on the cardiac
output.
So what happens when there is an increase in blood pressure?
First station: These baroreceptors will be stretchedand they will send
a signal to the vasomotor center which is located in the medullaoblongata, where we have tractus solitariaswhichis a collection ofnucleiin which we have vasoconstrictorand vasodilatorareas.
Second station: it is the vasomotor centers which is located in the
medulla oblongata, which is called tractus solitarias.
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Hypotension:
In case of hypertension, increase in blood pressure, these tractus
solitarias areas will stimulate the sympathetic nerves. Anatomically
theyre situated between T1 and L2 and they are called theparavertebral ganglion. So, signals on the vasomotor center will travel
to the sympathetic nerves then to the heart leading to an increase in
the heart rate and its contractility.
The sympathetic innervations are involved in increasing the heart rate
and its contractility. Why? Because sympathetic innervations innervate
mainly the ventricles as the bulk of the cardiac output is created from
the left ventricle.
So, the cardiac output will be increased due to the increase in the
contractility and heart rate and as the cardiac output increases that
means the blood flow will increase and increase in blood pressure.
Hypotension:In case of hypotension, the same Signals will be sent from the
baroreceptors to the vasomotor center but the main difference is that
the sympathetic innervations will be blockedrather than stimulated. So
the contractility will be decreased and heart rate will be decreased
In summary:
1-taractus solitarias stimulates -> sympathetic
nerves(paravertebral ganglion)
2-signals from sympathetic nerves travel to -> the heart
increasing its rate and contractility
3-cardiac output increases
4-blood flow increases
5-blood pressure increases
6-hypertension
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Reninis a protease which cleavesangiotensinogen to angiotensin I
Renin is secreted by the juxtaglomerularapparatus in response to:
1: reflexive sympathetic activity or betareceptor stimulation
2: decreased central volume of blood 3: decreased plasma Na+ 4: decreased distension of renal arteries
and cardiac output will be decreased thereby decreasing the blood
pressure leading to hypotension.
2-Long term regulation:
it means the regulation of blood pressure within minutes or more.
When somebody undergoes hemorrhage ( bleeding) they will enter in a
state of hypovolemic shock this means a decrease in bloodpressure
because the filling pressure(venous return) to the heart will be
decreased and in the end the cardiac output will be decreased so well
end up with hypotension which cannot be corrected by baroreceptors.So what exactly will happen?
Now when there is hypotension it will affect all the organs in the body
and in the state of a hypovolemic shock there will be an extensive
stimulation of the sympathetic innervations all over the body but
mainly in the kidneysand blood vessels.
In the Kidneys, there will be a decrease in blood flow. As a result Renin
will be secreted from the kidneys (due to low blood flow). Renin will
convert angiotensinogen, which is secreted from the liver, to angiotensin l
(an alpha globulin) which is inactive. Angiotensin l will be converted to
angiotensin by angiotensin converting enzyme (ACE) in the lungs.
Angiotensin
is very important andhas the following effects:
1-It is one of the most potentvasoconstrictors in the body.
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2- It enhances the secretion of aldosterone from the cortex of theadrenal gland. (Aldosterone will cause sodium and water
retention=hypertension).
3-It stimulates the reabsorption of sodium and water from theproximal tubules of the kidney.
4-It blocks bradykinin which is a vasodilator.
Heart Failure
NOTE
Heart failureis the inability of the cardiac output to keep
pace with the bodys demand for supplies and removal of
wastes. Either one or both ventricles may progressively weaken
or fail. When a failing ventricle cannot pump out all the blood
returned to it, the veins behind the failing ventricle become
congested with blood. Heart failure may occur for a variety of
reasons but the two most common are
(1)Damage to the heart muscle as a result of a heart attackor impaired circulation to the cardiac muscle
(2) Prolonged pumping against a chronically elevated bloodpressure.SHERWOOD
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COMPENSATED
ACUTE
#Heart failure: DECOMPENSATED
CHRONIC
As illustrated in the above diagram, heart failure is divided into acute
and chronic and the acute heart failure is further divided into
compensated and decompensated acute heart failure.
Compensated heart failure is the one in which rennin, angiotensinandthe aldosterone systemare capable of maintaining normal blood
pressure, and it can be regulated by long term regulation.
Aldosterone:
A Steroid hormone secreted by the adrenal medulla in responseto angiotensin II formation
Increases blood volume by promoting reabsorption of sodium Takes hours to be effective in raising blood pressure and volume
because it requires protein synthesis
NOTE: As you go towards high altitudes blood pressure will increase
due to hypoxia, also as you go towards low altitudes there will be
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Hormones effecting blood pressure
In the first lecture we said that the brain and endocrine system are
the systems of coordination. Now we have the suprarenal gland, the
medulla of this gland secretes
adrenaline and noradrenaline.They have their role in the
control of blood pressure
because adrenaline and nor
adrenaline causeperipheral
vasoconstrictionand central
vasodilatation. (Central means the heart)
Anti-puritic hormones also participate in maintaining the blood
pressure, they are also known as vasoconseen. It is the most potent
vasoconstrictor in the body, secreted from the hypothalamus it
enhances the reabsorptionof water from the collecting tubules of the
kidney and causes vasoconstriction thats why it helps in maintaining a
normal blood pressure.
Another mechanism for controlling blood pressure is the atrial
natriuretic hormone/peptide (ANP) which enhances the secretion of
sodium and water from the kidneys.
In addition we have a center in the brain called the Central nervous
system ischemic reflex, which affects the vasomotor center in
medulla oblongata, which is sensitive to the decrease in blood pressure.
Q: Why veins are innervated by sympathetic
innervations?
It relates to the function of the veins which is being
reservoirs of blood, so in case of sympathetic
stimulation as in when we are in the need of more
blood well get blood from here.
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Here are some useful diagrams for the lecture:
1-The Role of the Renin-Angiotensin System in Regulating
Arterial Pressure
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For more details go back to Sherwood or Guyton including the slides ..
they are useful..
Hope that you enjoyed the lecture,
Sorry for being late, forgive me if there is any mistakes
With my
1 Heart...2 eyes...5 liters blood...206 bones...1.2million Red Cells...
60 trillion D.N.A.'s...
I wish u "All the very best of luck"..
Done by: Sawsan Jwaied