Blood Pressure Regulation Script

8/3/2019 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

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Blood Pressure Regulation Script