The Cardiac Cycle is SO EASY! Stop Making it Hard!

listen the cardiac cycle isn't hard those super intelligent professors just make it complicated by the end of this video you're gonna understand it and if you don't i'll give you a million dollars wait wait no no no i i got carried away i i don't have a million dollars but stick with me to the end and you'll have a better understanding of how that amazing heart of yours works so let's do it [Music] hey this is leslie samuel here from interactive biology where we're making biology fun let's get into the cardiac cycle now when i say cardiac cycle i'm talking about everything that happens from the beginning of one heartbeat to the beginning of the next so we're dealing with an entire heartbeat now here's why it seems so difficult because when your professor teaches you about the cardiac cycle you see this complicated diagram right here it has a ton of details and it looks kind of scary let's not do it like that let's break it apart and build it back together but first let's look at what has to happen in a cardiac cycle let's start with the blood coming back from the body blood enters the heart first through the atria on the left side we have blood coming back from the lungs and on the right side we have blood coming back from the rest of the body when the atria contract they push the blood into the ventricles and when the ventricles contract they push the blood out of the heart those are the two contractions that cause blood flow are we on the same page nod your head and say yes now if you shook your head and said no check out my video on how blood flows through the heart and you'll get a more detailed explanation okay great let's move on the first place we're gonna look is at the electrocardiogram we're gonna start here because this shows the electrical signals that are responsible for the heart beating the first thing we see is the p wave this shows the depolarization of the atria that's the electrical signal traveling through the atria when this happens that causes the atria to contract so to see that we're going to look at a different line on this graph and this is the one that shows you the atrial pressure what do you expect to see right after the depolarization of the atria well that's the signal it tells the atria to contract and if the atria contracts you would expect to see an increase in atrial pressure right of course if you squeeze something the pressure increases and that's exactly what we see here right after the p wave makes sense i love it now there's a fancy word that goes along with this and that's systole whenever you see systole think contraction and here the atria are contracting so we have atrial systole simple what happens to the blood when the atria contract well it can only go one place it's going to go through the atrioventricular valves that's the one-way valves between the atria and the ventricles and it's going to go into the ventricles so what would you expect to happen with the ventricular volume you'd expect an increase in ventricular volume because you're filling it with blood and that's exactly what we see right here there's that bump in the volume of the ventricle so this entire section is what happens during atrial systole and just like that we're ready for the next step looking again at the ecg we see that the next thing that happens is we get the qrs complex now the qrs complex shows the depolarization of the ventricles you can see it's much larger than the p wave and that's because it's a much larger structure the signal is going to be larger and just like with what happens with the atria when you have ventricular depolarization you can expect to have ventricular contraction this is the beginning of the phase of systole where the ventricles are contracting when they contract what will that do to the pressure in the ventricles well during atrial contraction we did get a little increase in ventricular pressure of course because blood was rushing into the ventricles but now that the ventricles are contracting you're gonna see a much greater increase in ventricular pressure and it makes sense you have a container that you're squeezing and when you squeeze that container the pressure inside that container increases in this case the container is the ventricles it's made up of pretty strong muscle so we get a significant increase in pressure now there's a key thing that happens when the ventricles contract as you see here there's a short phase called isovolumetric contraction what exactly is that well the word isovolumetric means the volume stays the same in this case the amount of blood in the ventricles remains the same look at the ventricular volume it's pretty much a straight line and that's because when the ventricles start contracting that actually closes all the valves for example if we're looking at the left side of the heart this atrial ventricular valve gets shut and the semilunar valve is also closed if they're both closed we have a sealed container that we're contracting so we get this huge increase in pressure but that isovolumetric stage only lasts for a short period of time and that's until the semilunar valve opens here we're talking about the valve between the left ventricle and the aorta it's going to be closed up until a certain point now what point would that be well let's think about it on the other side of the semilunar valve is the aorta and at this point right here the aortic pressure is somewhere around 80 millimeters of mercury so if you want to push blood in there you have to have enough pressure in the ventricle to overcome that 80 millimeters of mercury and right at that point the semilunar valve will finally open and the blood can be sent into the aorta so that it can go to the rest of the body okay so blood is leaving the ventricle what will happen to the ventricular volume well it's gonna go down because the blood is actually leaving and that's exactly what you want you want the blood to leave the ventricles and go out to the body this stage here is the ejection stage that's when blood is being ejected from the heart and specifically the ventricles let's look back at the ecg we then have the t wave what does this t wave show well it's ventricular repolarization the opposite of depolarization so the ventricles are going to relax now what happens when the ventricles relax well the pressure in the ventricles will come back down and at a certain point the valves are going to close again and we get iso volumetric relaxation valves are closed ventricles are relaxing so the pressure in the ventricles drops significantly and that's exactly what you'd expect now once that ventricular pressure gets below the atrial pressure what's gonna happen to the atrioventricular valve it's going to open up again and at that point the valves are open and the blood that's coming back from the body will just start passively filling the ventricles and that continues up to the point where we get our next p wave to start the entire process again that's pretty much the cardiac cycle now there's one more thing that we didn't cover and that is this line right here which shows the phonocardiogram that shows the sounds of the heartbeat when you listen to the heartbeat like with a stethoscope you hear a sound that goes like this that's what you're seeing here what's causing that sound they're actually the sounds of the valves in the heart closing let's look at when they happen the first one happens right by the qrs complex remember that shows ventricular depolarization which causes the ventricles to contract and when the ventricles contract that push the atrioventricular valve close that's why you get to first sound the second sound happens after the t wave the ventricles relax and the semi-lunar valves close that causes the dub sound that's why you hear lub dub dub and now that is the entire cardiac cycle does that make sense if it doesn't watch it again pause it where you need to and get a good understanding of what this entire graph is trying to show my name is leslie samuel from interactive biology where we're making biology fun that's it for this video and i'll see you in the next one peace

Channel: Interactive Biology

Views: 981,438

Keywords: cardiac cycle physiology, cardiac cycle animation, cardiac cycle of heart, cardiac cycle ninja nerd, cardiac cycle khan academy, cardiac cycle phases, cardiac cycle graph explained, cardiac cycle, heart sounds, isovolumetric contraction, isovolumetric relaxation, cardiac physiology, ventricular ejection, atrioventricular valves, cardiovascular physiology, isovolumetric relaxation heart, end systolic pressure volume relationship, the cardiac cycle khan academy

Id: KmNHqqrFqG8

Length: 8min 43sec (523 seconds)

Published: Thu Mar 24 2022