We previously looked at how pressure changes in the ventricles, whether they're in systole or diastole, whether they're contracting or relaxing, is really going to dictate the movement of blood and the opening and closing of valves in the heart. Well, now we want to take those ideas and apply them to the actual heart and look at how this works through one heartbeat. The events of one heartbeat we call the cardiac cycle, the filling of blood into the heart and then the squeezing of the heart to push that blood into circulation. So as we start looking at the cardiac cycle, we're going to say that there are actually 4 events that we want to name and describe in this cardiac cycle, and we're going to break these events up based on sort of two factors. First, whether the ventricles are in systole or diastole. Remember, the ventricles, that's the main mass of the heart, and they contract with a lot of pressure. So whether they are in systole, that systole squeeze contracting, or whether they're in diastole, that diastole drops, the pressure drops during relaxation. Whether they're squeezing or relaxing, that's going to dictate these pressure changes more than anything else. So that's number 1. And number 2, we want to look at whether blood is moving in the heart. The pressure changes, we said, are going to open and close valves. Now you may think, isn't the blood always moving? But there's actually going to be some periods when all the valves are closed. All the doors in the heart are shut, so the blood actually doesn't move for some short periods, and that's going to break up this cardiac cycle some as well. Alright. So let’s take a look. You can see we have this image here of the heart. We have blood on it. Now this is going to be actually an animation. I’m going to play through this, so we can watch through the cardiac cycle. Now if you're following along on your student you'll see that we have you already have these phases of the cardiac cycle named, and you have freeze frames from this animation there. Now I like to show this animation because I think it's important to remember that this is a process. It doesn’t jump from one to the other. These are changes that flow from one to the other. So to get that idea, let’s watch one cardiac cycle first before we name things, And just know here we’re going in very slow motion. Alright. So first up, we have the blood flowing into the ventricles. The ventricles fill up. Now the ventricles squeeze. That closes the AV valve, pushes open the semilunar valve. The blood flows into the arteries. Now the ventricles start relaxing, that semilunar valve closes, then that AV valve opens again so it can fill. That was 1 heartbeat, 1 cardiac cycle. Alright. So let’s go through what just happened. So the first thing that happened, we’re gonna call ventricular filling. Alright. From that name, it should be pretty obvious what's going on here. The blood flows through the atria and into the ventricles. Now, as we go through this, for each one of these stages we're going to try and name: are the ventricles in systole or diastole? Is the ventricular pressure high or low? And are the AV valves and the semilunar valves open or closed? So, for ventricular filling, if blood is flowing into the ventricles, well, that means that the ventricles must be in diastole. Remember, diastole means that they are relaxed. That means that there's very low pressure, so the ventricular pressure is going to be low. And we can see here on the image I’ll actually just advance it just a little bit here. We had that blood flowing into the heart. That means that the AV valves those are open those valves between the atria and the ventricles because the pressure in the ventricle is lower than the pressure in the atria. The semilunar valves, you’ll see those are closed because the pressure in those arteries is going to also be greater. Well, this time, it's going to be greater than the pressure in the ventricles. Alright. So we’re going to fill up, and then those ventricles are going to start contracting. So I'm going to advance our video here. They start contracting. Those AV valves close, and I'm going to stop it right there. Alright. Here, we've started contracting. The AV valves have been pushed closed because the pressure has risen, but you can see the semilunar valves, those valves from the ventricles into the arteries, they haven’t opened yet. So we're going to call this stage isovolumetric contraction. And again, if we break down these words here, we can see what's happening. ISO, well, ISO means the same, and volumetric it refers to the volume. The volume isn't changing, but the ventricle is contracting. So we’re gonna say here the blood is contained in the ventricles as they contract. Alright. So what's happening in these things we want to fill in? Well, the ventricles, they're contracting, so that means that they are in systole. We have that systole squeeze going on. That means that well, if they're contracting, that means that the pressure in the ventricles well, I’m gonna say here it's rising. It’s not as high as it's gonna get, but it is going up. We can see the pressure has risen enough that the pressure in the ventricle is now greater than the atria. That has pushed that AV valve closed, But the pressure in the ventricle has not gotten enough to be greater than in the arteries, so that semilunar valve is also closed. Alright. All the valves, all the doors to the ventricle are shut. So it means even though it's contracting, the pressure hasn’t changed enough to actually move the blood, so we’re in an isovolumetric stage. The volume is staying the same. Alright. Pressure’s gonna keep rising though, and we'll follow this along. It's
Table of contents
- 1. Introduction to Anatomy & Physiology5h 40m
- What is Anatomy & Physiology?20m
- Levels of Organization13m
- Variation in Anatomy & Physiology12m
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- Introduction to Tissues & Histology16m
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- 14. The Autonomic Nervous System1h 38m
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- 17. The Blood1h 22m
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- 19. The Blood Vessels3h 35m
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- Introduction to the Immune System10m
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- Primary and Secondary Response of Adaptive Immunity21m
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- Natural Killer Cells16m
- Review of Adaptive Immunity25m
- 22. The Respiratory System3h 20m
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- 24. Metabolism and Nutrition4h 0m
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- Introduction to Cellular Respiration22m
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- Cellular Respiration: Pyruvate Oxidation8m
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- Cellular Respiration: Chemiosmosis7m
- Review of Aerobic Cellular Respiration18m
- Fermentation & Anaerobic Respiration23m
- Gluconeogenesis16m
- Fatty Acid Oxidation20m
- Amino Acid Oxidation17m
- 25. The Urinary System2h 39m
- 26. Fluid and Electrolyte Balance, Acid Base Balance Coming soon
- 27. The Reproductive System2h 5m
- 28. Human Development1h 21m
- 29. Heredity Coming soon
18. The Heart
Cardiac Cycle
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