Physiology, Lecture 14, CVS 2

8/8/2019 Physiology, Lecture 14, CVS 2

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Cardiovascular system 2

Wan najib


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Bismillahirahmanirrahim.

Now as I told you before, when we have an excitation of SA node, It will cause the depolarization of autrium,

plateau, then repolarization. Next the impulse, will cross the AV node. It will go to AV bundle. To the ventricle. And

depolarization of ventricle, plateu, and repolarization of ventricle.

*please refer the labeling from your book.

1. Wave P -Atrial depolarization- opening of sodium channel in SA node

2. Segment PR Atrial Contraction- Opening of Calcium channel

3. QRS Development of Atrial repolarization-Development of Ventricle Depolarization

- Opening of Calcium channel in atrium

- opening of potassium channel in Ventricle

4. Segment ST - Ventricular contraction-opening of Calcium channel

5. Wave T Ventricle repolarization-opening of potassium channel

6. TP interval resting-no channel opening but only leakage of sodium

We cannot record the Action potential of SA node directly on the heart because it is too small. When We record it

through the body surface, the result is not the actual one. It will be lesser than the actual one ase usually record the

ECG in the lab by using two electrodes and a voltmeter. One of the electrodes should be positive and another one

should be negative. If both of the electrodes is negative/positive, there will be no deflection. Deflection only occur

by two electrodes with different charge to each other. If the current move towards the positive electrodes, the


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reading in the voltmeter will show positive deflection. While if the current move towards the negative electrode, the

reading in the voltmeter will surely show negative deflection.

The picture above shows the method of recording the action potential of SA node.

We connect the right arm with the left arm by the two electrodes and a voltmeter between them. The right arm is

the negative terminal due to the excitation of SA node producing action potential on the right atrium(positive

terminal). Remember that the right side will be always negative. In this case, the current will move from the right

arm to the left arm producing positive deflection. So, this connection is known as Lead I.

Then, the right arm (negative terminal) will be connected with the left leg(positive terminal) producing positive

reflection too. This connection is known as Lead II

The same thing happens between the left arm(negative terminal) and the left leg (right terminal). It also produces

positive reflection .This connection is known as Lead III.

Mechanical Event of the Cardiac cycle.

When the blood comes to the heart, it will first accumulate at the right atrium. Both of the atrium will contract while

the both ventricles will relax at the same time. The contraction of atrium will produce higher pressure region in the

atrium that cause the blood flow towards the lower pressure of ventricles through the AV valve. The blood will flow


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rapidly and this process is known as rapid filling. Not all of the blood in atrium flow to the ventricles successfully. And

this is condition is known Diastasis.

Now the blood accumulates in the left ventricle. The pressure of left ventricle is higher than the left atrium. The

blood cant flow back to the atrium as the AV valve prevent it to do so. At the same time, the pressure in the aorta is

still higher than the pressure in the left ventricle. So, the left ventricle need a mechanism which is the contraction of

left ventricle which can provide a higher pressure to move towards the aorta. With this higher pressure, the right

ventricle can penetrate through the Aortic valve

Isovolumetric contraction is the first part of systole to increase the pressure without changing the volume. When the

pressure is successfully increased over the aortic pressure, the blood now can start flowing through the aortic valve

towards the aorta entering the ejection phase.

When the pressure in the aorta starts become higher than the ventricle. The aortic valve will start to close.

At this time, the Isovolumic relaxation will gradually decrease the pressure in the ventricles so that it will be lower

than the atrium like before in the first stage.

So you have two period of cardiac cycle which are systole ( contraction and emptying) and diastole (relaxation andfillings)

During this diastole period, the blood will move from atrium towards the ventricle. The rapid filling is due to atrial

contraction.

When the contraction finished, systole period will take place. The first part of systolic period is the isovolumetric

contraction (increase pressure without changing the volume). When the ventricle pressure exceed the aorta

pressure, the aortic valve will open for the blood flow causing the ejection phase.

After the aortic valve is closed, (due to the reduction of ventricle pressure compared to aorta pressure) the dystole

period will take place again by the isovolumic relaxation.

The beginning of systole is when one of the valve is opened and the isovolumetric contraction occur (to incrse the

ventricle pressure). While the beginning of diastole is when all of the valve is closed and the isovolumic relaxation (to

dcrse the pressure).


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The first part is the ECG. And second part one is the cardiac cycle. The purple line symbolize the pressure in aorta.

The red line symbolize the pressure change in left ventricle. The green line symbolizes the pressure in left atrium.

Imagine as far as the green line of left atrial pressure, as far as it is above the red line of , it means that the pressure

in atria is higher than in the ventricle. So the blood flows from the atrium to the ventricle. Now at this point, this is

the atrial contraction. And then, the

Then, the red line is gradually increase until it exceeds the purple line of aortic pressure. This means the starting of

ejection phase. After that, the red line is gradually decrease until it reaches below the the green line of atrial

pressure. This indicates the starting of Isovolumetric ventricular relaxation.

The third part is about the volume of left ventricle. Based on the second part above, during the green line is higher

than the red line, the volume of left ventricle increases as the atrium pumps the bloods into the ventricle itself.However, by the time the red line of ventricular pressure increases rapidly, the volume in the ventricle is becoming

constant due to isovolumetric ventricular contraction (increase pressure, without increasing volume). After the

ventricle undergoes the ejection phase, the volume of left ventricle start to decrease rapidly, as the blood flows to

the aorta while emptying the ventricle. During this time, the ventricle is decreasing its pressure without changing its

volume. This is what we called as isovolumetric ventricular relaxation.

The fourth part is about the heart sounds. When AV valve closes, it will produce sound. This sound is called as first

sound. It symbolizes the end of diastole and the beginning of systole. Then, there will be a second sound. This

sound means the end of systole and the beginning of diastole.


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Cardiac Outputs

When the blood leaves the heart, we dont pump all the blood through aorta. Some of the blood will stay in the

ventricle specifically in Chordae tendinae and papillary muscle. So we have this filling volume which we call it as N

diastolic volume. After the ejection, we will have the N systolic volume. The different between these two path is the

volume blood pumped per liter which is called as stroke volume. Stroke volume is the volume blood which can be

ejected there only. Then we have cardiac output is the volume of blood which can be found either on the left or rightventricle per minute.

Cardiac output (CO) = HR x SV

Cardiac index is the volume of blood which is ejected per minute per square meter.

And lastly, the doctor said that hell continue about the cardiac output next time. enshaAllah.

The end.

~ Guys, Im so sorry for this last minute work. The doctors lecture is kinda distorting. So its kinda hard for me to

rearrange back the point as he repeated the same points many times. Hopefully, It may still benefits anyone. Sorry

again. Good luck!~

p/s: I recommend you guys to refer back to the book and slides because there is some terms that Im not sure with

it.

Done by: wan.

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Physiology, Lecture 14, CVS 2