Lesson video

Hello and welcome to today's lesson.

My name is Mr. Swaithes.

I'm really looking forward to teaching you today.

So we're going to be exploring the cardiac cycle, and that means digging into the detail of what happens when our heart actually beats.

(thumps heartbeat rhythm) When the blood moves from and where that blood moves to.

Have you ever wondered why your heartbeat makes that "ba-dup" sound? If so, this is the lesson for you.

Today's lesson is called The Cardiac Cycle, and it comes from the Anatomy and Physiology: The Cardio Respiratory System Unit.

By the end of the lesson, you will be able to describe the mechanics of a heartbeat.

This is a really nice lesson to cement that understanding of the cardiac physiology, but it also gives you a chance to get hands-on and mould a replica heart out of Play-Doh or Blu Tack.

Or if you don't have any of that available to you at home, then why not combine with a bit of home cooking and make yourself some pizza dough and then mould with that (rubs hands) before you make yourself a pizza later.

So the keywords for today's lesson are: cardiac cycle, so that's about the sequence of events in a heartbeat, including the contraction and relaxation phases.

And going into more detail there, the systole is when the heart is contracting, which causes blood to be ejected from the heart, and diastole is when that heart is relaxing and therefore filling with blood again.

You may want to pause the video for a moment and make a note of them, but I will explain them again fully as we come across them in the lesson.

So our lesson today is split into two parts.

Firstly, we're helping you really understand that cardiac cycle and how it has two main phases, and then secondly, gonna help you understand that sequence of events in a cardiac cycle.

I hope you're ready.

Let's get started.

Okay, so Izzy was wondering about the heartbeat.

She was saying, "If you listen to your heartbeat carefully, you can hear that ba-dum, ba-dum, ba-dum, ba-dum sound.

But why does it make that noise?" What do you think? If you've got the opportunity, discuss that with a partner before we move on.

Okay, so that cardiac cycle is the sequence of events that happen every time the heart beats, and the order of that is as follows: First of all, the heart relaxes.

This is called diastole.

So the posh word for relaxation phase of the heart is diastole, and during that phase it fills up with blood that's been returning into the heart from the veins.

So we can see that in illustration one.

And then after that, the heart contracts, and that is called systole, and it, first of all, contracts in the top chamber.

So the atria.

So let's have a quick check.

Which of the following statements is correct? Is it A: Diastole is the phase of the cardiac cycle when the heart muscle contracts to pump blood? Or is it B: Systole is the phase of the cardiac cycle when the heart muscle relaxes and fills with blood? Or is it C: Diastole enables the heart to fill with blood ready to be pumped out again in the next heartbeat? That's right, Diastole enables the heart to fill up with blood ready to be pumped out again in the next heartbeat, whereas the word systole is connected with contraction.

Okay, let's move on.

So we'll see the second half of that cycle, and we can see here that the tricuspid and bicuspid valves close and that prevents the backflow of blood from those bottom ventricles from squeezing back up into the atria.

Next up, those ventricles contract.

So the heart then squeezes from the bottom of the heart.

So if you like, the "ba" is the top atria contracting, squeezing blood down into the ventricles, and then the "dum" is the bottom chambers, the ventricles contracting, and that ejects blood up and out of the heart because the bicuspid and tricuspid valves are closed.

So it can't go back up into the atria, it's gotta get ejected from the heart into the arteries.

And then the whole cycle repeats itself with blood flowing back into the atria as it returns from the veins.

It'll start to trickle down into the ventricles, then those atria contract, the systole stage, then the ventricles contract, the systole stage, blood's ejected out of the heart, and then diastole, the relaxation again.

Okay, so let's just do a quick check.

True or false? The systole occurs when the heart contracts.

Is that true or false? That's right, it's true.

So systole is a posh word for contraction, and it is actually split up into two parts, as we've just seen.

So the blood is squeezed down from the atria first in that "ba" phase, or the atrial systole, and then it goes on down into the ventricles where they contract.

So that's actually called the ventricular systole.

So the "dum," that second part of the heartbeat.

So.

(mimics heart beating) And here we've got a nice little illustration of the that as it happens.

Let's just watch that through a couple of times.

Okay, another true or false then, to check your understanding.

The left and right sides of the heart go through systole and diastole at different times to each other.

Is that true or false? That's right.

It's false.

So the coordinated wave of contraction that happens in both sides of the heart at the same time.

So both atria contract, squeezing blood down, then both ventricles contract, squeezing blood up and out of the heart.

And that's thanks to a really specialised type of muscle called cardiac muscle that's all interconnected and it contracts in sequence involuntarily.

And if you've ever heard of someone that's gone into cardiac fibrillation, that basically means that that mechanism has stopped working properly.

So instead of it pulsing in that exact sequence, the heart is just kind of contracting randomly and almost spasming in different directions, so it's not operating properly.

So that's why we go and get the defibrillator, or hopefully the paramedics get the defibrillator and we give the heart a bit of a shock to restart it and get it back into that nice wave of contraction, where the atria contract, then the ventricles contract, squeezing blood out.

It relaxes, diastole, and fills with blood.

And then the atria contract, the ventricles contract, and blood squeezed out again, into the left and right sides at the same time.

And of course, we've got that septum wall in the middle of the heart that stops the blood in the left and right sides from mixing.

Because one side is dealing with oxygenated blood, whilst the other side is dealing with deoxygenated blood, and you wouldn't want those mixing.

Okay, so both the atria and the ventricles go through systole, and then when the atria contract, blood is squeezed down into the ventricles, and then when the ventricles contract, blood is squeezed up and out of the heart.

Valves between the atria and the ventricles close off once blood has been squeezed through.

And that prevents backflow.

Then valves between the ventricles and the arteries, so that's the pulmonary artery and the aorta.

Those valves also close off once blood has been ejected at high pressure to stop it from coming back.

Okay, now it's time for your first task.

So what I would like you to do is answer the following questions to secure your understanding of the cardiac cycle.

So firstly, can you describe the difference between diastole and systole? Secondly, can you outline the function of the tricuspid and bicuspid valves in the heart? And then thirdly, can you explain what is going on when the heart makes that "ba-dum" sound as it beats? Pause the video now whilst you have a go at that, and come back to me when you are ready.

Okay, let's have a little look at what you've come up with.

So for question one, what is the difference between diastole and systole? Hopefully you've captured something around the fact that diastole is that relaxation.

So the keyword there is the relaxation phase.

And during that diastole, the heart fills up with blood, whereas systole is the contraction phase.

So that's where the blood will get ejected from the chambers of the heart.

Question number two.

So this was about the function of the tricuspid and bicuspid valves in the heart.

Well, as we know, valves prevent backflow of blood.

So that means that when it's been squeezed from the atria down into the ventricles, we don't want it going back up into the atria, so back in the wrong direction.

So what the bicuspid and tricuspid valves do is they stop blood that's got down into the ventricles from going back up into the atria.

And then the third, the most challenging of these questions was why does it make that "ba-dum" sound as the heart beats? Well, the "ba," the (mimics heartbeat) So that first bit represents the first part of the contraction phase, or the first part of systole, and that's when blood is squeezed from the atria, down into the ventricles.

And then that second half of the heartbeat represents where the ventricles are contracting next, and that squeezes blood up, out through the arteries and around the body or to the lungs, depending on whether it's the left or the right side.

So between these sounds, there's then a relaxation phase called diastole, and that's super important for the heart to fill back up with blood.

And as we know, when we start to exercise, or in fact even when we get nervous, we can feel our heart beat faster, but also more forcefully.

Next time you go for a run, perhaps pay attention a little bit to that sensation, that feeling of that heartbeat and that, (mimics heartbeat) and remember what it is that's going on during that.

Okay, onto the second part of this lesson then.

And as I promised at the beginning, this is the chance for you to get a little bit creative.

And here I want you to explain the sequence of events in a cardiac cycle.

So we've already said that when the heart is relaxed, that is called diastole and it can fill with blood.

So the blood's returning to the heart through the venous system, but then what's gonna go on next is the brain will send a message down these neural pathways, so down the spinal cord and in through the nerves, and that initiates the contraction phase of the heart.

So that cardiac systole.

And it's an automatic thing, you don't need to think about it, it's an involuntary thing.

But when that systole happens, so when the heart contracts and squeezes, that increases the blood pressure inside the heart.

And of course that's gonna force those valves open and squirt the blood up, out of the heart at really high pressure, but also at a fast velocity.

And then the valves prevent that blood from coming back in the wrong direction.

So then, let's have another quick check.

Which of the following diagrams is incorrect? Notice incorrect.

Is it A, is it B, or is it C? Take a moment to look carefully, and in particular look carefully at the arrows.

That's right, it's A, because A is incorrectly suggesting on that left hand side of the heart, so highlighted in red, it's suggesting that the heart comes in through the aorta, down into the left ventricle, then up out of the left atria and out around the body.

And of course we know that actually, the pathway of blood is in the opposite direction to that.

So that was a tricky one.

But it should look more like picture C where it's coming down and then out.

And of course, actually, the heart is a 3D structure.

So when we take these cross sections, they're not actually 100% anatomically correct.

If you've ever dissected one in Science, you'll have seen it slightly different to this.

Okay, so let's have a quick check for understanding.

True or false? During diastole, the heart is filling with blood.

That's right, it's true.

So if the heart doesn't relax between contractions, there would be no opportunity for it to fill up with blood, and hence there'd be no blood in it ready to get pumped out again in the next beat.

So it's that relaxation phase that's super important.

And because it's coming back in at lower pressure, that relaxation phase is often longer than the contraction phase.

And that brings us nicely into the second task for this lesson.

So this is the one where I really want you to create your own 2D mould or model of the heart.

And I want you to remember to dissect your heart so that we can see all of the chambers inside it.

And then to add labels to it.

If you are unable to get creative with some 3D modelling that you can squash out to be 2D, then maybe just draw this on paper, labelling all the chambers up correctly.

Pause the video now whilst you have a go at it, and then we'll have a chat through what you've come up with.

Okay, here's a couple of examples from lessons that I've taught.

So we can see an example on the left hand side there.

We've got a really creative little picture of the stick person, and that's illustrating the body and you can see the labels on there.

And then the lungs at the other end of the heart, and you can see the red left hand side illustrating oxygenated blood, whereas the deoxygenated blood, we didn't have any Blu Tack, sorry, Play-Doh.

So that's been done in green.

And then you can see the valves as those little pipes in between.

And then on the right hand side as we look at it, there's a slightly different illustration of those chambers, and I'd hope that you'll be able to label that one up carefully.

Okay, so that brings us to the end of today's lesson on the cardiac cycle.

So by means of a quick summary: The cardiac cycle is the mechanics of a heartbeat.

It consists of two main phases.

Can you remember, what were they called? That's right, we've got the diastole, or the relaxation where it fills with blood.

The systole, which is the contraction phase where it will then pump that blood out, first of all down into the ventricles and then up, out of the heart into the arteries.

Really important to remember that the septum is that muscular wall that divides the left and right sides of the heart to help prevent oxygenated blood from mixing with de-oxygenated blood.

Now will be a really good time to have a go at a few other past paper questions.

I hope you've enjoyed this lesson and look forward to seeing you next time.