11th Class Biology Chapter 11 | Electrocardiogram | Class 11th Biology New Book 2025

Added: 2026-05-12

[00:00:07]Assalamu Alaikum class. This is me Ghulam Nabi your biology teacher. Okay dear class, the topic we are going to start today is Chapter No. 11 Human Circulatory System. His article is Electrocardiogram. DI students is a very important topic. It will also be a little critical. Ok? The topic will be a little difficult. So you have to attend 24 lectures and it is very important to attend previous lectures because all the concepts will be revised there. DI Students Now What is Electrocardiogram Basically? See, the word electro is related to charges. Ok?

[00:00:40]Cardio is related to the heart and gram is related to the cardiogram.

[00:00:45]Gram is the recording of anything inside the cardiogram or you can say that if you are recording anything on any special type of page or on any structure then it is called gram. So now basically what is an electrocardiogram? An electrocardiogram is basically a recording of electric potentials generated by currents of cardiac impulses. Now see what will be the cardiac impulses? Specific impulses or electrochemical changes or signals that are generated within the heart.

[00:01:17]fixed bugs? So the current will be of electrocardises.

[00:01:21]fixed bugs?

[00:01:26]What is generating that current of cardiac impulses? Electric potential. Now I will give you a complete brief introduction about electric potential. So what is it basically? Electrical Electric potential that causes cardiac impulses What is happening? It is being created.

[00:01:47]What do you do with the electrical potential that is being generated due to the impulses being generated inside the heart? Let's record it.

[00:01:49]Ok? There will be special types of devices that will do what? Will record. So this is called electrocardiogram.

[00:01:57]In simple words, it is also called ECG. You must have seen that often patients are taken to such doctors, so shows are being conducted like this, waves or segment shows are being conducted.

[00:02:08]So basically what it is is recording the electrical potential of the electrical current inside the heart, this is called ECG.

[00:02:18]What happens to DI students now?

[00:02:21]In ECG, it tells us that when cardiac impulses pass over the surface of the heart, whenever cardiac impulses or electrochemical signals pass over the surface of the heart, a minute electrical current will be generated due to its passing. What will be generated? Minute electrical current will be generated. What happens now? This current spreads into the tissues surrounding the heart.

[00:02:50]What does this current do to all the tissues surrounding the heart? It spreads, it spreads. What now? This minute electric current also travels to the surface of the body. What does it do to the surface of the body? Passes out or travels. Now what are DI students? It has a very simple mechanism.

[00:03:07]Rods are installed on both sides of the body. Two electrodes are placed on both sides of the heart.

[00:03:12]One side positive and one side negative. What is done to it with a special type of device?

[00:03:18]is connected. Then what is done from inside it? Now he talks about what generates the electric potential? By this current. What happens inside the ECG is that the electrical potential is created by the current generated due to the cardiac impulses of the heart.

[00:03:36]Now this electric potential is generated due to cardiac current or due to the current of cardiac impulses. This is measured or recorded in an ECG.

[00:03:48]Now what happens for this purpose?

[00:03:51]Electrodes are placed on the skin opposite the side of the heart.

[00:03:55]Electrodes are placed on the opposite side of the heart.

[00:03:57]One side positive and one side negative.

[00:04:00]What happens now? These electrodes are connected to a special type of machine called electrocardiograph.

[00:04:07]Now what that electrocardiograph does is that when it passes an electric current, the electric potential that is generated due to the passage of that current is recorded.

[00:04:20]What happens to the electric potential that is present near the current? is generated.

[00:04:22]What does it do with that electric potential? Record. Okay dia students next is ECG. If there are any different types of abnormalities in the conduction system of the heart, like conduction of nerves, conduction of pulses, then what does it do in detecting them? She helps. Next, the ECG shows waves of electrical impulses produced at specific events of the cardiac cycle. In the different cardiac cycles we have studied SA node, AV node. Different systole, diastole. So during this, some specific electrical impulse waves are formed and ECG shows them at different times of different cardiac cycles.

[00:05:04]Now, before starting the topic, I will first give you a brief introduction as to how electric potential is basically generated? How is a nerve impulse generated? DI Students Let's Suppose You Have a Sale.

[00:05:18]You have to understand this very carefully because the entire topic will depend on this. There is a cell, inside it there is negative charge. Basically what you have is cardiac muscle cells or nerve cells. Right now we will have cardiac muscle cells because we are talking about them right now. Now how is electric potential generated in these? If then there is negative charge on the inner side and positive charge on the outer side. So this type of state is called polarized state. What do you say?

[00:05:51]Polarized state. Now what are the heart cells or muscles doing in this state? Relax. Relaxed means the body is not doing any kind of conduction.

[00:06:04]What happens now? When they relax, what phase does that mean? This is the diastolic phase. Which phase is it? Diastolic. Whereas at the time when blood is flowing inside the heart chambers. What are all these phases basically a part of? This is part of the polarized state. What do you call this?

[00:06:26]G. Polarized state. You have to remember the word polarize well. Now what is the condition on the other side? Now, at the time when the electric impulse has to be generated, what happens at that time, dear students? These charges are reversed.

[00:06:41]What are these charges? Reverse. If earlier it was negative inside, now it will be positive inside and what will be on the outside? Negative.

[00:06:48]These are basically sodium and potassium. Sodium positive and potassium negative. At this time, in the second state, potassium will come out and sodium will move inwards. DI students, this fuzz is called depolarization.

[00:07:01]What do you say? Yes. Well, this is also resting fuzz.

[00:07:04]This is relaxing. And basically you will also call it resting potential.

[00:07:09]Resting because there is no conduction of charges of any kind.

[00:07:14]But what happens inside this fuzz which is osit depolarization, what do all the cells do? Let's make a contract. The heart muscles will contract. That means this is systolic fuzz. Ok?

[00:07:29]And this is depolarization. That means the charges on the inner side will become positive and those on the outer side will become negative.

[00:07:36]Now contraction occurs in depolarization.

[00:07:39]fixed bugs? There was relaxation here. Here the contract is systolic. This diastolic will be called depolarization. The second thing we saw was this. Third state: When depolarization or contraction occurs, then ultimately the process of relaxation begins. So in relaxation, what will happen third is that the charges will reverse again.

[00:08:00]Negative on the inside and positive on the outside. So DI students, what do we call this fuzz? We will call this fuzz repolarization. What will you say?

[00:08:10]Repolarization.

[00:08:13]Now see, first of all whatever happened in polarize, its opposite happened in depolarize.

[00:08:19]After that, when the same thing happens again which happened in the polarized state, what is it?

[00:08:23]Repolarization is also the same. Because what does repolarize mean?

[00:08:28]What is going on sale again? Are getting polarized.

[00:08:31]Meaning coming back into the resting fuzz.

[00:08:33]Ok? So there will be no contraction of any kind in it and at the same time it is also diastolic. Okay dear students, you have to look at these three concepts carefully. This has to be revised.

[00:08:44]Now this should be in your mind.

[00:08:46]So we will easily draw a structure of an ECG and look at its different segments. DI Students ECG as you can see. You might have seen such waves moving across the screen in videos or movies. So this is basically the structure of an ECG. There are many parts inside it.

[00:09:04]Now, if a part like this comes in the structure of ECG, then the DI students will call this part wave.

[00:09:12]If a completely straight structure is coming, what will you call it?

[00:09:17]Segment. And if you suddenly get the right like this, then you will call it a complex. So you have to keep this structure in your mind. The structure will be straight then segment.

[00:09:26]Wave must have been made like this. First comes the DI students P wave. It has a wave structure. Now what will happen in the wave structure? Now I will correlate it with this and tell you. See the first process is G atrial depolarization.

[00:09:41]Beginning of atrial depolarization.

[00:09:43]When does atrial depolarization start?

[00:09:46]When the atria do what? See, when we read that the current is generated in such a node which is the first node and is present on the top side inside the atria.

[00:09:57]fixed bugs? From there the impulse will start generating. So what will happen now is where will atrial depolarization initiate? From the S.A. node. From where? From the S.A. node. Now there is atrial depolarization. So see what does depolarization mean? I told you the meaning of depolarization, that it involves contraction.

[00:10:16]This is the systolic fuzz and it does n't have this resting potential inside it. This is the conduction fuzz through which the nerve impulse has to be conducted. So now he's talking about atrial conduction, that means the current will pass easily through this tube.

[00:10:31]Ok? So due to which atrial depolarization occurs. Atrial depolarization means that nerve impulses are being conducted. fixed bugs? So the very beginning of atrial depolarization, who does it? The impulse will be generated from the S node and within it.

[00:10:50]Now when the impulse is generated, this fuzz will come. The negative charges will come out. Positive charges will move inside.

[00:11:00]What does that mean will happen inside the atria because of this process? There will be contraction. There will be contractions inside the atria.

[00:11:05]Atrial contraction is taking place here. That means atrial systole is happening here. Ok? Now what if there's some kind of abnormality in this, okay? If a disorder occurs, what happens is that if there are irregular or absent P waves, it can cause arrhythmia. What does arrhythmia mean? That the special kind of rhythm of the heart in which that heart beats, what will that rhythm ultimately become? It will be disturbed. So this is called arrhythmia. Now let's see what is basically being generated? P-wave. And see what does wave mean? It is that it is slightly raised above the simple line. So that means this wave structure means that electric current is passing through here.

[00:11:46]Now this wave can be even more.

[00:11:48]Look, this wave can be this much and can also be like this. So basically what will it show more or less of? Intensity of impulse. How much current is passing through there or what intensity of impulse is being generated there. So that height decides on the basis of how much amount or how much concentration of impulse it passes, whether it is more or less. DI Students Next segment we have is PR segment. Now look here, I told you about this segment which is the state part. So this is how you can see it in the diagram also. This segment which starts exactly after the P wave is called the PR segment. Now what does this PR segment show? Shows completion of atrial depolarization. Now the atria was getting depolarized, meaning the nerve impulses were being conducted from inside. fixed bugs?

[00:12:37]Now he is showing his completion.

[00:12:40]What does completion mean? That now the process of atrial depolarization or conduction or contraction is moving towards completion. So when it gets to completion, what does that mean? What fuzz is coming to us? Meaning he is going to be repolarized again. So that means resting fuzz is coming again. So DI students, remember one thing, this process gets completed in 0.12 to 0.20 seconds.

[00:13:04]And ultimately the state of repolarization is achieved. That means why do we have this PR segment? Because now the atria are going into a state of relaxation.

[00:13:17]Now he is not doing any contraction. That means the state of repolarization is coming. Meaning the cell is moving towards polarization again.

[00:13:25]Ok? Negative charges are moving outwards and positive charges are moving inwards. So this is how the charges are being exchanged. So this was the G PR segment. If it gets prolonge d, it means PR segment. Like I have created this segment, this is the normal segment.

[00:13:39]If this straight line segment becomes very long, it means that first degree heart block is occurring. This means that there is some first degree blockage in the heart. And this means if it is not contracting for a long time or is remaining relaxed then that means first degree heart block is happening. So this is its abnormality show. DI Students next is QR, it is called QR Complex.

[00:14:03]QR S Complex. What is QR S complex? This basically shows the beginning of depolarization of the ventricles. Now Atrias has signed the contract. What has happened to her now? I became relaxed. Now basically atrial systole is complete. Now we are moving towards ventricular systole in which the ventricles contract.

[00:14:22]So when will the ventricles contract? What will happen when the ventricles fail?

[00:14:26]Depolarization. Not a polarized state but depolarization in which it has to contract.

[00:14:30]Meaning charges are being exchanged, positive on the inside and negative on the outside.

[00:14:34]Now, D.A. Students, what is the atrial repolarization that we have, basically? See Atrial Repolarization Also Akers During This Fuzz. If the ventricles are depolarizing in QRS, then that means we read that the atrial depolarization that happened behind it has been completed.

[00:14:53]So if that depolarization is complete then that means the atrium has to repolarize now.

[00:14:58]So he is saying that in the QRS complex itself the atria repolarization is getting completed and what happens to the depolarization of the ventricles? It begins.

[00:15:09]Now if there is depolarization then that means the ventricles have to contract and you know that the ventricles contract with a lot of intensity because they have to send blood throughout the body. So that means look, the segment you can see, the QRS segment, is fine. In this segment, the ventricles contract so fast at a very high height due to which its height increases and you can see on both sides that the QRS segment goes a little downwards from the normal level.

[00:15:38]So this means that you can say that the charges here are not opposite in direction but you can say that the charges are moving opposite to each other inside the inclined surface, like this is positive and on the other side it is negative, so because of this a slight depression is generated in the middle of the qRS segment, so this is not a part of our topic, we are only looking at the qR segment, so now what happens in the qR segment if qR is not a RS segment, sorry students, this is complex.

[00:16:12]If there are abnormalities within the QR complex, then these abnormalities will basically be related to the ventricle somewhere.

[00:16:18]So this can indicate that what was the bundle branch that we had, DI students? This is the SA node and this is the AV node. Two branches emerge from the AV node, left and right.

[00:16:30]So that bundle branch can get blocked. Apart from that, ventricular tachycardia. Tachycardia means an increase in the heart rate.

[00:16:39]So the heart rate will increase. That means the rate of contraction is getting faster.

[00:16:43]So can ventricular tachycardia. The ventricles are contracting too rapidly or some other ventricular abnormalities may also be related to the QR complex.

[00:16:54]Student Next we have ST segment. DI Students ST Segment What do we basically have? The ST segment shows us the completion of depolarization of the ventricles. The ventricles contracted. What do the ventricles have to do now? Have to relax. So basically the depolarization of the ventricles is moving towards completion. So what do you mean the ventricles are starting to become again? It has started to repolarize. So what happens inside it now? Can we depress in Ishamiya.

[00:17:25]This ventricular depolarization process can also be depressed, and the specific state or disorder that it can cause is schizophrenia. What is Skimmia? Basically decreases blood flow to the heart muscles. That oxygen to the heart muscles or blood flow to the heart muscles may decrease. Inside whom? In the ST segment.

[00:17:47]Now look at this, after this as soon as this QR complex is completed, this structure which you can see is the segment being formed. What does segment mean? If it is a straight line then that means contraction is not taking place. He is moving towards relaxation. So these issues can occur within the ST segment. And ultimately, it can also cause myocardial infection. Because the heart tissues are getting less oxygen. So the disease that occurs due to less availability is called myocardial infection. And ultimately this segment lasts for 0.08 seconds.

[00:18:17]DI students have finally come to us, what are you calling the last wave? T wave. Now what do we have, the T wave? These represent the present repolarization of the ventricles. So depolarization is getting completed there. Ok? So that has become a state.

[00:18:33]Now here he talks about the repolarization of the ventricles represented within the T wave.

[00:18:39]Now what will happen to the ventricles? Repolarization.

[00:18:45]What does repolarize mean dia students? Which state is he coming into again? He is coming back into his resting condition.

[00:18:54]Now, the abnormality within the T wave can be such that it can cause electrolyte disturbance.

[00:19:01]We read about electrolytes earlier also, like we have charges. There are different types of electrolytes, different types of ions. What can happen if there is a disturbance because of them?

[00:19:11]Abnormalities may occur within the T wave.

[00:19:14]And in the last, D.A. students, in this he talks about hyper acute T wave. What if the T wave is what it is? Hyperacute shows earliest findings of acute myocardial infection. What if the T wave becomes too high? It becomes hyper acute. May it grow up. fixed bugs?

[00:19:35]So because of this he says that the earliest findings in this show us that acute myocardial infection can occur.

[00:19:42]Now lastly, Di students qt which is q and t interval, that means all this space between q and t is called qt interval. Now what happens inside it?

[00:19:52]Where does this start from? It starts from the QRS complex and ultimately ends near the T wave and the normal QT wave, sorry QT interval, lasts for 0.40 seconds. DI Students now we have a side box in your book called Blue Babies or Cyanosis. We will see this. This is a special type of disorder. Blue babies means those babies whose skin color is not blue. Now the blue skin color means this disease is called cyanosis. Now why does this happen?

[00:20:22]Because inside their body, oxygenated blood and deoxygenated blood are mixed together.

[00:20:26]That means they do not separate well. We know that the right side contains deoxygenated blood and the left side contains oxygenated blood. So the heart maintains specific separation between them through the interatrial septum and the interventricular septum. So what happens now is that this oxygenated and deoxygenated blood gets mixed together.

[00:20:44]Due to which this mixed blood goes throughout the body. Due to which cyanosis occurs. Now why does this happen?

[00:20:50]Because, D.S. students, when a baby is developing, during the development, when it is developing inside the mother's body, due to that a special type of foramin is formed inside its body. A special type of closing is created. Closing means someone who will close something. Now that closing is called inter atrial foramen. Now what does inter atrial foramina mean? That one takes the right atrium and the left atrium. A special kind of closing is created between these two. It is called inter atrial foramen. So what happens is that during development, what happens to this foramin? It does not close.

[00:21:27]What this means is that this foramina or this opening between the two atria, the inter-arterial foramina, fails to close properly, that is, you can say that it fails to close or fails to close.

[00:21:41]So it remains open during development.

[00:21:45]Due to which, what happens between the two atrias, the left and the right, and the mixed blood keeps flowing continuously? The exchange continues.

[00:21:53]So what happens because of this? Blue babies and other conditions that occur during development.

[00:22:00]This is called ductus arteriosis.

[00:22:08]What does ductus arteriosis mean? This is something or the other that is related to the arteries.

[00:22:12]Now DI students what happens is that during development itself you have two arteries. The one that comes out from the right side is called the pulmonary artery. It contains deoxygenated blood. And you know the one that comes out from the left is called Iota. Now what do these two arteries do? There is no construction between these two or they contract and constrict.

[00:22:39]So now because of the constriction, what happens to the blood that is inside both of them, the di students? Live separately. Deoxygenated blood and oxygenated blood remain separate.

[00:22:50]Now what happens is that the construction or contraction of these two arteries inside ductus arteriosis does not happen properly. Meaning they will not separate from each other again.

[00:23:01]The construction is not happening properly.

[00:23:03]What will happen because of this? The blood will mix up.

[00:23:06]Oxygenated as well as deoxygenated.

[00:23:09]And this mixed blood will spread throughout the body. Then the disease that it causes will be called cyanosis or blue babies. fixed bugs? Cyanosis means that the amount of oxygen in the blood decreases. This is called cyanosis. So dia student it was all from today's lecture which was we had electrocardiogram. Hope you understood the lecture. Take care of yourself. Allah Hafiz.