Heart Physiology

Hi. In this video we'll be looking at the physiology of the heart and examining how the heart pumps blood. No, the heart circulates blood generally by filling up its chambers from the veins and then pushing that blood through the arteries. Now the veins are going to empty into chambers known as atria. These air thinner, less muscular chambers than the ventricles and the ventricles, which are more muscular than the Atria, are going to be the powerful pumping stations that push that blood through the arteries of the body. So, really, the atria are there to receive blood and move it into the ventricles. And the ventricles are the guys who do the rial heavy lifting and actually push that blood into the vasculature. Now the act of pumping by the heart is known as the cardiac cycle. This is a a complete cycle off, pumping out blood and filling up with blood. It's divided into two phases, known as Sistol and Dia stole. Sistol is the contraction phase where the muscles of the heart are going to contract and blood is ultimately gonna be pumped. Dia stole is the relax ation phase, which is going to allow the heart to actually fill with blood. Now me jump out of the image here. And let's talk about what's going on with our atria and our ventricles during these two phases. Now, when the atria and the ventricles are in Dia stole blood is going to flow into those atria and ventricles. So here we are in Di a stall and you can see that blood. This is our superior vena cava. Here's our inferior vena cava. These are Veena ka vie, Right? So from the Vienna Cav, I blood is going to enter into our me actually switch colors here, so it's easier to see on the blue background. This is our right atrium, and this is our right ventricle. So blood is going to flow into these. And on the other side we have our left atrium and left ventricle. And of course, the left atrium is going to be receiving blood from the pulmonary artery. So here we have Veena cover. And here I'm sorry. I said pulmonary artery. I meant pulmonary vain. So these chambers are going to fill up now. The atria are going to experience Sistol before the ventricles do so. The atria are going to be in Sistol, the ventricles in diastolic. And what What this is going to allow for is the blood in the atria to be pushed through those Avie valves, those atrial ventricular valves and fill up the ventricles. Then the Atria are going to go into Dia stole. And, um, the ventricles are going to go into Sistol, and that's gonna push the blood from the ventricles. And you can see this over here. Push the blood from the ventricles into the arteries through those semi lunar Valle's. So this whole process is recorded in electrical signals that look like this, right? If you've ever seen, like, a doctor show or a movie where there's a scene in the hospital, there's always a machine in there that has, like, little green screen or something with this little line going across it. And it's like but but boop that's monitoring the heart rate. So this whole, uh, blip right here, if you want to call it that is actually recording the electrical signals that air going through the heart during heart contractions. So let's actually flip the page and talk about how those electrical signals start and how they propagate

the heart beats in response to electrical signals we call action potentials. We'll learn more about these in the chapter on the nervous system. For now, just know that these air electrical signals that air generated by moving ion cross the membrane of cells. Now action potentials in the heart are not transmitted by nerves like we'll see throughout the nervous system. These action potentials actually move between the cells of the heart through what are called gap junctions. Gap junctions, which you can see right here have are basically direct cell to cell connections. And there are these channels between the cells that ions can flow through these channels, air referred to as connections. You don't need to worry about memorizing any of this. Just know that the action potentials in heart cells are moving cell to cell through gap junctions. In fact, there's actually a specialized structure in heart muscle that connects neighboring cells and contains these gap junctions. We call those inter Kalay tid disks and here is an example of some heart tissue, and if you zoom in, you can see some inter Kalay tid disks between the cells. Now here we actually have a recording of an action potential. And hopefully this looks a little familiar to you, right? That blue, blue, blue, That line that you see on the heart, the heart rate monitor, right? The thing in the hospital that we just looked at it looks a heck of a lot like that, right? It is, in fact, measuring what is known as a, uh, the electric potential. Something measured in volts. It's a type of voltage. You don't need to worry about remembering any of this. I just want you to see the similarity between this standard image of an action potential and what we see appear on the heart rate monitor because they're, uh, you know, basically measuring. You know the same thing. Now, how do these action potentials get generated? Well, there is a special part of the heart, a group of cells in the right atrium that are referred to as the Sino atrial node. And basically, these cells are going to be responsible for initiating heart contractions, invertebrates. There's actually a group of cells there that air usually referred to as pacemaker cells, and these air thesis cells that will control the rate and timing of heartbeats and they are going to actually start, Uh, the action potential. They're going to be the initiator of the action potential? No, from the s a node, as it's often referred to, the action potential is going to propagate to what's called the a trio ventricular node, which is a group of cells that is sort of it's almost like the center of the heart. You can see the A V node being pointed out here. So our s a node was up here. The action potential moves down to the A V node and at the A V nodes, something interesting happens. See that signal? That electrical signal is delayed, and the reason for that is we want the atria to have a little extra time to completely empty its blood into the ventricles. So by having a slight delay in the signal at the A V node before it moves down into the ventricles, we actually give the atria at the time. It needs Teoh. You know, push all the blood has out into the ventricles, making the work of the ventricles contraction more efficient. No, When the signal goes down into the ventricles, something kind of interesting happens. So from the A V note, it actually goes down to basically like the bottom of the ventricles. And from there it's propagated up through the ventricles through these five fibers called perkin gee fibers Perkin E fibers. You may hear it pronounced, depending on whether you give it a softer, hard J. Anyhow, these Perkin gee fibers will actually spread the action potential up through the ventricles from the bottom to the top. Now, the reason for this is the arteries have their openings located kind of at the top of the ventricles. Use a different color here, make these arteries like red. So by having the ventricles start there, contraction from the bottom and move it up. You're actually pushing the blood up into these arteries. That's the reason for it. Now, this whole process, this whole electrical process is recorded in what's called an electrocardiogram. Sometimes it's abbreviated, E k g. If you're wondering why it's not e k c e k g comes from the German word. Uh, so, you know, kind of confusing there, but it's the same thing E K g is an electrocardiogram. So this is going to record the electrical activity of the heart and it's going to be output looking like this. So at the start here we have our s a node that is going to lead R s. A note is going to initiate theatrics in potential. This is going to be the big contraction of the ventricles. And here we have relax ation of the muscles so you don't need to worry about memorizing the different parts of the E k. G Signal. Just wanted to sort of show you how these electrical signals correspond to the phenomena that we've just been talking about. So with that, let's actually flip the page.

Now let's put together everything we've just talked about into one concise package. So let's begin with Dia stole, which is again the relax ation of the ventricles and atria, which is going to cause them to fill up with blood. All right, that's what we're seeing here, right? The ventricles and Atria are going to fill with blood. Then, as we can see in our E k G signal, the S a node is going to initiate the action potential. And that's going to cause the atria to contract or atrial Sistol, if you will. We have atrial Sistol, which means that our right Atria and Left Atria are going to empty their blood into the ventricles. We could see that happening there now, before our ventricles contract. Remember, there's a slight delay and you can actually see that in the signals. This little like flattening right there. That's the slight delay of the A V node, right? Delaying the action potential, which is going to allow the Atria two completely empty into the ventricles now insist All remember, the action potential is going to start at the bottom of the ventricles and move up through the parking. Gee, fibers. This causes the ventricles to contract and push blood into the arteries. And R E K G. That's this big, deep polarization. That's the fancy science term for it. There, it's, you know, the big electrical signal right there. That's that big ventricle contraction. And you can see that happening in these images. Here we have our ventricles, super full of blood looks, left ventricle. These guys air super full of blood in this image right here. And then we're going to get contraction in this image, right? Those ventricles, they're getting squeezed, and they're gonna push the blood into the arteries. Those are, of course, the pulmonary artery. And this guy right here, the aorta. So after that, we're going to have Relax ation, right? Go back to Dia. Stole after Sistol. And that's going to cause the atria and then, eh, ventricles to fill back up with blood. And that relax ation could be seen on the E k G here at the tail end. Now, this whole process is again called the cardiac cycle, and we like to measure it in certain ways. I mean, we look at the electrical signals with the KGB, but sometimes we want to know about, uh, other facets of the cardiac cycle, one of which is cardiac output. And this is going to be the volume of blood that's pumped per minute by the ventricle. So this is a rate of volume per minute, and it's basically looking at two measurements and putting them together. Those measurements are heart rate, which is heart beats per minute or beats per minute. And you know, this is often written, for example, in music as BPM, Right? If you like that electronic like dance music, you want those high bpm, you know, obviously our heart rate we don't want Thio be too high. But a very interesting thing to note is our heart rate is around 60 beats per minute, right? They beat every second and A and dance music Some of the most popular dance music is actually at about 120 beats per minute. Double the heart rate, right, So kind of an interesting thing to take note of how you know something is obscure is like or abstracted from nature as Elektronik music still is grounded in biology, right? We can't help but like things that you know, Uh, that adhere to our natural cycles, so to speak. Now getting a little distracted. Let's get back to cardiac output. The other measure that is involved is stroke volume, which is the volume of blood pumped by a single ventricle. Contraction. So this is not a rape. This is just a volume. So combining heart rate and stroke volume, you can get cardiac output and see how much of blood is being pumped per minute. Let's flip the page.

Hello, everyone. In this lesson, we're going to be talking about blood pressure and how blood pressure is going to change. Depending on the different veins, arteries and capillaries. The blood is actually in. Okay, So first off, let's talk about the two different types of blood pressure. So I'm sure you've had your blood pressure taken by your doctor. And your doctor gives you these numbers. Generally, there are around 120 over 80 and that actually is your blood pressure. But it's actually two different versions of blood pressure. Thes systolic. Blood pressure is the top part of the fraction, and the diastolic blood pressure is the bottom part of the fraction. So what's the difference between these two? Because if you are a pre med student, you're definitely going to have to know these two different types of blood pressure. Okay, so the first one, the highest number, is going to be your systolic blood pressure. And this is the highest blood pressure that your arteries should actually experience and that your heart should actually experience and systolic blood pressure is going to be taken at the time. In the heart phase is called Sistol insist all is going to be the peak of contractions. So this is the peak of blood pumping out of the ventricles. So whenever the ventricles actively contract and push that blood out of the ventricles, that blood's gonna be of extremely high pressure because those muscles are actively squeezing on it. So systolic blood pressure is the highest blood pressure because this is going to be the pressure off the blood when the ventricles are actively contracting during the phase called Sistol. So Sistol is going to have a range of healthy blood pressures. And during the contraction phase or systolic phase thehuffingtonpost blood pressure should be so. The optimal blood pressure should be less than 120 millimeters of mercury, which is going to be a measurement of pressure. So anything less than 120 millimeters of mercury is good. So around that range is a good systolic blood pressure. Anything above 1 40 I believe, is going to be problematic and is going to cause high blood pressure, which is not good for your body. Okay, so now the second form off blood pressure is the diastolic blood pressure. This is going to be the one on the bottom of the fraction when you're given your blood pressure and this is the lower blood pressure that you experience. And it's the lower blood pressure because it's actually right before the ventricles contract and pump out blood. And this is because this is going to be the blood pressure of the DIA stall phase in the heart contraction phase. And this is actually the relax ation phase. And this is actually when the chambers of the heart are refilling with blood right before the contraction phase right before Sistol. So this is going to be the very low blood pressure of the heart and of the blood, because this is when the heart is relaxing and when the heart is actually refilling with blood so it can do another cycle of contractions. And this blood pressure also has an optimal blood pressure. And this is anything under 80 millimeters of mercury. Anything above that is considered high blood pressure and can be dangerous. So that's why they say that you want your blood pressure to be around 120 over 80. So let me draw this out for you guys, so your fraction would look like this. 120 over 80 millimeters of mercury. And this one right here is the systolic. And this one right here is the diastolic. So that's why you get two numbers whenever you get your blood pressure reading. Okay. All right. So now we use blood pressure to understand how the heart is functioning and how the blood is moving through the body. We also utilize pulse and pulse is actually going to be measuring the bulging oven artery during the heartbeat. So whenever your heart is beating, your arteries actually will bulge because the pressure and the force of the blood is increasing. So you guys can generally put your hands up next to your neck and find an artery, and then it will be pulsing. And that is because with every beat in contraction of your heart, more blood is being pushed through that artery. So it is going to expand. Okay, so the pulse is going to tell you about the heartbeat. How quickly are those contractions happening? And the blood pressure is going to tell you the pressure of the blood and how much force is being put on that blood. Okay, so now let's talk about high blood pressure because Americans do have an issue with this, and this is also called hypertension. And hypertension is long term, high blood pressure. This is anything over 120 especially over 140 for systolic blood pressure. Anything over that for a very long period of time is called hypertension. Hypertension is generally seen in Americans because we have a very high salt diet. But hypertension can be caused by, ah, high salt diet. Ah, high fat diet and a lack of exercise and hypertension can lead to a lot of issues. You can imagine if you have a lot of pressure on your heart and on your arteries in your veins at all the time throughout your entire life. You're going to have some issues from that, and this can cause coronary artery disease. This can cause a stroke. This can cause kidney disease and can cause a whole bunch of issues. So hypertension is generally bad, and this is generally medicated for or the diet has changed. But I want you guys to know that this is generally caused by diet, but it can also be caused by genetics as well. Some people have a higher propensity toe have hypertension than others. Okay. All right. So now let's look at this really neat graph which is going to be showing us The pressure's off these different areas of your cardiovascular system. So what we have is we have the pressures of these different vessels. So you have the aortic pressure, which is going to be the pressure of your aorta, which is the largest vessel in your body. And the left ventricle is going thio push blood into the aorta and we're going to have the pressure inside of the Atria is, and we're gonna have the pressure inside of the ventricles. Now, just do you guys know whenever you're measuring blood pressure, you're generally measuring the pressure of the aorta, the major arteries of the body. So whenever you're looking at these pressures on this chart, the one we generally go by to measure pressure of the blood is this one in red right here. The aortic pressure is generally what we utilize. And if you guys can see the way we know that is true is because we have the 120 we have the 80. That's the general healthy blood pressure for an individual. And that's how you know this is the one that we're measuring. We're measuring the aortic pressure. Okay. All right. So you guys know that we're measuring the aortic pressure, and I would like to show you the different phases off the hearts contraction. So the phase that is happening right here is Sistol. So this is the contraction phase. All of this right here is the contraction phase. And you guys can see that during the contraction phase, the aortic pressure is going to go from 80 all the way up to 120. That's gonna be the highest pressure when those ventricles air actively contracting and pushing the blood out. And then once this doll is ending, that pressure is going to go back down right around 2. 80. And that's because that is the filling stage. So this is going to be diastolic, and this is going to be diastolic as well. This is when the heart is actively refilling with blood. So the pressure here is much lower and you guys can see that the Atria and the ventricles also do change in pressure. You can see the ventricle pressure in black changes substantially. You guys can see that it's way down here. And then during Sistol, it just jumps up to these huge pressures. And that's because the blood inside off the ventricle is being actively squeezed and being given a ton of pressure. And it's just shooting that blood out of the ventricles. And then it's going to dramatically dropped back down during Dia stall, and the drop in blood pressure actually aids the heart and pulling more blood into it. So this is basically showing you the different pressures that the different areas of the heart and the different vessels experience. So the order is in red, and that is what we generally utilize for blood pressure. That's what we used to read. Blood pressure is the aortic pressure, but then we also have the ventricular pressure in black, and we have the atrial pressure in blue, and they're all going to vary. But the one that's most dramatic is the ventricular pressure, because it greatly jumps up during Sistol. Okay, guys. All right, so now let's go down and let's talk about how the blood vessels air going to deal with this gigantic change in pressure because the arteries are the vessels leading away from the heart and they're going to experience the most intense blood pressure, especially the aorta, which is going to experience the most intense blood pressure because that left ventricle is actively pushing blood into it. So the way they're going to combat this is that arteries have muscle fibers and elastic fibers. Help them deal with the high pressure. So this is going to be these muscle fibers, and these fibers that help it stretch and help it go back to its normal size during the different contractions of the heart. And the aorta is especially dense with these elastic fibers because it goes through this immense systolic blood pressure. This immense change in pressure every time those ventricles contract. Those fibers are there to help that to help make sure that these arteries don't burst. They need to be able to withstand this giant change in pressure. So now the arteries are going to have the highest blood pressure. The arteries air the vessels leaving away from the heart, and the arteries are the vessels that are actively being pushed blood into So they have the highest blood pressure. The veins and the cap pillories are gonna have the lowest blood pressure. Remember the cap Pillories are where nutrients and gas exchange are going to occur with the tissues of the body. And these are the smallest blood vessels, and then the veins are going to lead the blood back to the heart. So blood obviously is going to slow as it moves farther and farther away from the heart. And as it moves through the capital Aries, it is going to slow. And this is going to cause a substantial drop in velocity and pressure of the blood. But don't worry. Our bodies have ways to deal with that. So veins were going to have the lowest blood pressure and they're going to have these valves inside of them which arteries do not have. And these valves air going to ensure that even though this blood doesn't have a lot of speed and it doesn't have a lot of pressure, these valves air going to close to ensure that blood doesn't go back the wrong way, that it continues on its route to the heart and something really cool is veins in your extremities, like your legs and your arms and your hands are going to move through skeletal muscle. And then why do you think they move through skeletal muscle, where they're gonna move through skeletal muscle? Because every time you move your arms and your legs or any of your muscles, it's going to help create pressure to move the blood through the veins. So even though the veins don't have a lot of pressure from the heart, they are going to receive pressure from you moving your body, which is going to help blood move back to the heart. So it's really good to get up and walk around every once in a while when you're sitting at your computer or something like that to help your blood keep moving. Okay, all right, so now let's talk about the capillary specifically, so I have a diagram of a cap Hillary system right here and Cap Hillary's are going to deliver so many different things to our body tissues. So Cap Hillary's are important for delivering oxygen and taking away carbon dioxide. They're important for delivering water and delivering nutrients. They also take away wastes like uric acid and lactic acid that build up in ourselves. And they're basically the exchange system between the blood and the cells and guys, the the fluid that surrounds these cells that actively interacts with the cap. Hillary's is gonna be the interstitial fluid, and this is the fluid that leaks from the capital Aries and surrounds the cells. This is fluid in the blood, but it's not actively red blood cells. So this is where all of the nutrients and all of the gas is air going to be dissolved. And whenever the fluid leaves the cap, Hillary's it's going to do exchange with the cells. Now, whenever we're talking about pressure, we're going to have the arterials, which are the arteries that lead to the capital Aries, and we're gonna have the venue ALS. And the pressure in the arterials is relatively low. But in comparison to the venue ALS, it's high. So there's high blood pressure over here, and there's going to be low blood pressure over here, so this poses an issue. How does the blood actively go through this system? Because what's going to happen is blood is going to enter the arterials, and then it's going to enter the cap Ilary. And then, ah, lot of the fluid is going to leave the blood into the interstitial space. So how does the blood get that fluid back if the pressure is very, very low. So the pressure has dropped dramatically because a lot of the fluid has left the blood. So the pressure pushes the fluid out of the blood into the capital Aries into the interstitial fluid. Now, how does the blood get that fluid back? Well, the way it's going to get that fluid back is now the solute concentration in the venue. ALS is going to be incredibly high because all of the fluid left the blood. It left all the salts behind. But because all of the fluid left the blood and that left all the salts behind that osmotic pressure is going to be very high in the venue. ALS and the fluid is going to want to return to the blood to decrease the solute concentration. So, through osmosis, the fluid will return back to the venue ALS because the salt concentration is very high in the venue als So in the arterials, the fluid leaves the blood because it has high blood pressure. Now how does it get back into the venue? ALS Because of high osmotic pressure, Because the water is actively going to go back into the blood because of osmosis to counter act that very high solute concentration that is found in the venue ALS. So even though it sounds like a really complex process, it's not particularly complex. Basically, what you guys need to know is that the heart is going to push blood into the arteries and they're going to experience extremely high blood pressure. And then the arteries are going to lead to the capital Aries, where the exchange of nutrients and gasses and waste is going to occur. And the high blood pressure is going to push the fluids with all those dissolved nutrients and gasses out of the blood system into the interstitial fluid. But how does the interstitial fluid get back? It is going to get back via osmotic pressure, and it is going to re enter into the venue ALS because of osmosis and then the venue ALS are going to lead to the veins, which we're going to use their valves and their skeletal muscle to push the blood back into the heart so that the whole process can start all over again. Okay, everyone, let's go on to our next topic.

just like other systems in the body. Blood pressure has to be controlled in a homey of static manner. And barrow receptors are going to be thes pressure sensors that help detect blood pressure in the heart and the arteries. Now, obviously, uh, you know, a certain level of blood pressure needs to be maintained, and blood pressure is going to be affected by things like blood vessel dilation and constriction as well as blood volume E. I mean, you know, if you have more blood volume, you will be able to generate a greater pressure, however, by, for example, constricting blood vessels. You can create greater pressure even with, you know, a lower blood volume. So there's many different mechanisms to kind of essentially tweak and fine tune to get the optimal blood volume and pressure. So one thing that the heart will do is increased cardiac output in response to low blood pressure. Right. Your blood pressure is low. Well, pump more blood thio sort of counter act that affect another thing is, uh, you know, if the body is experiencing low blood volume or, uh, you know, uh, is actually will happen due to a variety of other reasons as well. But blood can be diverted to important tissues. For example, during like a fight or flight response, you know you'll have blood diverted away from digestive tissues because if you know you need to fight for your life or run away or something, you don't really need to be worrying about digesting your meal. And this is accomplished by, uh, constricting specific arterials. Thio, you know, ensure that more blood is going to be more important. Tissues, for example, like in a fighter flight scenario muscles, right. You obviously want a lot of blood going your muscles so you can fight or run away. Do whatever. However, this sort of tweaking can also be helpful if you're experiencing, uh, lower blood volume and need to ensure that, you know, like the brain is still getting sufficient blood supply. So by constricting blood vessels, the the body can regulate blood delivery to various tissues. Now, additionally, uh, veins can constrict to divert more blood volume to the heart and arteries so it doesn't have thio. Thes effects don't have to apply across all blood vessels, you know, in this example, the veins can actually constrict themselves to uh, supply less space for blood to hang out so that there's gonna be mawr blood necessarily in the heart and arteries, which is, of course, you know, the important place toe have the blood because, uh, you know the arteries, they're going to deliver it to the tissues, whereas the veins, they're just bringing it back to the heart. And lastly, blood pressure gets too high. You can dilate your blood vessels and lead are an initiate a drop in blood pressure by creating more, uh, are less resistance to the flow of blood. Now, ah, this nifty little image just sort of shows you generally like percentages of blood being delivered to various tissues. Just think it's interesting. And here I'm just trying to show that there are actually many different types of regulators that are connected to the heart. So these air supposed to represent, um, a bunch of different neuron aled connections or nervous system connections to the heart that can modify, uh, the pumping of blood and influence, you know, blood pressure. Of course, you know, there's many other mechanisms aside from thes story synaptic connections to the heart, which will provide, um, you know, home, you know, static system to fine tune blood pressure and blood volume. So what about when things go wrong? Well, we call diseases that affect the heart or vasculature cardiovascular disease, Very creative name. Now one of the most common types of conditions. You may have heard of his arterial sclerosis. This is the hardening of the arteries due to an accumulation of fat deposits. This has to do with this stuff cholesterol, which is very important molecule. We use it for a lot of different stuff, including producing steroid hormones. And they play a very important role in membrane fluidity of cells. And you've probably heard of, um, good cholesterol and bad cholesterol is sort of like the, you know, layman terms that are used to describe what are actually known as low density lipoprotein and high density lipoprotein. Now, low density lipoprotein is what people refer to you as bad cholesterol, and the high density lipoprotein groups is good cholesterol, and this is a bit of an oversimplification. But the reason that we think of them this way is that, uh, LDL delivers cholesterol in the body, and so it's going to be responsible for those deposits you know, if you have, uh, too much, Um, you know too much LDL. You're gonna have a lot of cholesterol coursing around your body, and it can lead to these accumulation of fat deposits that will lead Thio arterial sclerosis, which is bad HD Els. We call good cholesterol because they actually scavenge the excess cholesterol. So they're like the cleanup crew they get. They pick up all that allow that deposited stuff and, you know, help prevent arterial sclerosis. Now, a myocardial infarction is the fancy name for a heart attack. And this is essentially when one of the coronary arteries gets blocked and this leads to damage of the heart muscle tissue, super serious, bad stuff. Lastly, um, I want to mention what a stroke is, which is damage to the nervous tissue in the brain. And usually the reason we're talking about this in relation to the heart is because usually strokes will be caused by a lack of oxygen getting delivered to the brain tissue due to some sort of blocked or ruptured artery in the brain. So a lot of scary stuff we talked about here, I hope it doesn't give you nightmares. That's all I have for this video. Keep your heart healthy, guy.