Lesson video

Hello and welcome to today's lesson.

My name is Mr. Sways, and I'm looking forward to teaching you today.

We are going to be looking at the double circulatory system and also at the structures of the heart.

We'll be unpicking how it works in a figure of eight, and also the different chambers and valves in the heart.

Today's lesson is called the Double circulatory system and structure of the heart, and it comes from the Anatomy and physiology: the cardio-respiratory system unit.

By the end of the lesson, you'll be able to describe the pathway of blood through the double circulatory system and explain its importance in maintaining efficient blood flow.

So I've already mentioned that the heart works as a double pump, but what do you think that means and why is it so important? The keywords for today's lesson are: atria, ventricles, valves, pulmonary circulation, and systemic circulation.

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

So in our lesson today, we will first of all understand how the double circulatory system works and how one loop is concerned with collecting oxygen from the lungs and taking it back to the heart, whilst the other loop's job is to deliver that oxygen to the working muscles and also to collect carbon dioxide as a waste product from exercise, bring that back to the heart and then back out to the lungs.

So we will then explore the names and locations of the different chambers, valves, and structures of the heart to understand how blood flows through it and in what order.

You might have learned about some of this already in science.

I hope you're ready.

Let's get started.

As I'm sure you already know, the heart is responsible for pumping blood around the body.

It delivers oxygen to the body or to the muscles more specifically, and I guess also the brain and other body organs.

And it removes waste products, including carbon dioxide.

So carbon dioxide is a waste product of respiration, and the job of the heart is to then pump that carbon dioxide back to the heart and then on up to the lungs so that we can expel that carbon dioxide.

So why do you think oxygen delivery is so important to us for exercise? And also, which body system or systems does the heart work with to deliver oxygen? Okay, so the cardiovascular system is another name for the circulatory system, and it's made up of two parts: cardio, meaning heart, and vascular, meaning blood vessels.

It's responsible for circulating that blood around the body, and as I just said, it is also known as the circulatory system.

So that part answers that previous question.

But we also need to remember that the cardiovascular system is made up of the heart, the blood vessels, and the blood.

And then it's also really helpful to remember that the cardiovascular system works really closely with the respiratory system, so your lungs.

And I guess the respiratory system is responsible for bringing that oxygen into the body and getting rid of carbon dioxide.

And then gaseous exchange occurs at the lungs to enable oxygen to enter the bloodstream.

Okay, so a little bit more detail about the heart, the blood vessels, and lungs, because they're sometimes referred to collectively as the cardio-respiratory system, and it's really important you look at questions carefully to see, are they asking you about the cardiac system, i.

e.

just the heart, the vascular system, i.

e.

just the blood vessels, the cardiovascular system, i.

e.

the heart, the blood vessels, and the blood, or the respiratory system, so just the lungs, or in this instance, the cardio-respiratory system, which is all of cardiac and respiratory.

And then linking this back into the muscular system and the skeletal system, of course we know that once we've got that oxygen and nutrients into our body and around to our muscle site, that's what provides energy for exercise, and hence the musculoskeletal system takes over to turn that oxygen and nutrients into movement.

So that answers the second part of that question there around, you know, what happens, what's the importance of this when we exercise.

Okay, so it's really clear then, isn't it, that for exercise and to play sport, we need a constant supply of oxygen to provide the energy to keep us moving.

Even at rest, we need constant blood supply to keep living tissues, including the brain, as I mentioned earlier, alive.

So that's why we continue to breathe even when we are resting and our muscles continue to require oxygen to keep the living tissues, to keep them alive.

Meanwhile, carbon dioxide, or CO2, is that waste product of respiration.

And if we don't remove carbon dioxide, it can cause a number of problems. For example, shortness of breath, dizziness, fatigue and weakness, and also impaired performance.

So it's actually getting rid of excess carbon dioxide that's really important as a part of that exercise and breathing process.

Okay, let's have a quick check.

Which of the following body parts make up the circulatory system? Is it A, the heart and lungs; B, the heart, blood vessels, and blood; C, the heart, blood vessels, and lungs; or D, the muscles, bones, heart, and lungs? That's right, it's the heart, blood vessels, and the blood.

Okay, so we need to identify that there's left and right sides to the heart.

And actually this can be quite confusing because the left side of the heart is that nearest your left armpit.

So this is the left side of my heart, whereas this is the right side of my heart.

But then when we draw it on a piece of paper, we've got a diagram in front of us, it appears that the left hand side of the heart is drawn on the right hand side of that image when it's on paper.

All right? So yeah, it's almost reversed as if you are the body lying on the page and you're looking at that left side which is nearest the right hand side of the piece of paper.

It's often also helpful to, yeah, think that the blue side that we often draw these are the deoxygenated blood, and that's on the right hand side, whereas the red side of the heart is that oxygenated blood, which we'll see here.

Okay, so you can see here that when the heart contracts, it squeezes blood out.

And the heart is made up of this specialised cardiac muscle that contracts to squeeze blood from the top chambers down into the bottom chambers, and then the bottom chambers out of the heart.

The left side of the heart, as I said, receives oxygenated blood from the lungs.

So you can see it there at the top right hand side of that picture, the red arrow coming from the lungs and going in through the pulmonary vein into that top left hand chamber.

Although as we look at it on paper, it's on the right hand side.

And we'll learn a bit more later on what those different chambers are called.

But that's red lines illustrating oxygenated blood, or oxygen-rich blood, and then it's pumped back out of the heart again and on around to the body where that oxygen is delivered to the working muscles that are needed, in this example, this person that's doing a hurdles race.

So then meanwhile that oxygenated blood releases its oxygen to the muscles and picks up carbon dioxide as that waste product of respiration, and it's then called deoxygenated blood.

So there's not very much oxygen in it anymore, but there is lots of carbon dioxide, and we tend to draw that in the colour blue.

Often you'll see in your veins they look a blue colour, and that's because they're not rich in oxygen like arteries are.

So that deoxygenated blood returns to the right hand side of the heart before it's then pumped out again to the lungs.

And you can see that figure of eight there, the double pump system.

Let's have another quick check.

So, people often get confused with labelling the sides of the heart.

Which of the following is correct? Is it A, the left side is nearest the left armpit.

It is actually on the right side when you look at a diagram on paper.

Or B, the left side is nearest the right armpit.

It is correct when you look at a diagram on paper.

Or C, you can label the left and right sides either way.

Hopefully you got that one right.

So the answer was A, the left side of the heart is nearest your left armpit, but when you look at a diagram on paper, it is actually at the right hand side.

Okay, another important feature here is the septum.

So that's the wall down the middle of the heart and that divides the left hand, right sides of the heart.

So the job of the septum is to prevent that oxygen-rich or oxygenated blood on the left hand side from mixing with deoxygenated blood on the right hand side.

And it forms kind of a network of blood vessels that look like a figure of eight, as I said earlier.

So you can see that figure of eight of blood flow.

So the double circularity system then, it operates as two loops, and that loop that's going up to the lungs and back to the heart is known as the pulmonary circuit, whereas the loop that goes from the left side of the heart out to the body and then back in with deoxygenated blood to the right hand side of the heart is known as the systemic circuit.

So we've got the pulmonary circuit going to the lungs and the systemic circuit going to the body.

Okay, let's have another check.

True or false? The pulmonary circuit carries blood from the heart to the body to supply oxygen for respiration.

I hope you got that one correct.

So the answer is false.

And why? Because the word pulmonary relates to the lungs, hence the pulmonary circuit carries deoxygenated blood to the lungs to collect oxygen, whereas it's the systemic circuit that carries blood to the body.

So what I would like you to do now is consider this discussion between Lucas and Aisha.

So Lucas is saying, "Why are some of the blood vessels on the diagram shown as red, whilst others are shown as blue?" And Aisha has said, "Is it something to do with oxygen content?" I'm wondering, is Aisha right? And with the help of a diagram, can you, firstly, label the pulmonary and systemic circuits? And then secondly, colour in the red and blue vessels with a sentence to explain their colour.

Pause the video and come back to me when you are ready.

Let's check what you came up with.

So hopefully you've got a diagram similar to that one where you've identified the pulmonary circuit, which carries deoxygenated blood to the lungs to collect oxygen and return to the left side of the heart.

And then the systemic circuit that carries oxygenated blood to the body and returns to the right side of the heart.

Blood vessels carrying oxygenated blood are shown in red, whereas those carrying deoxygenated blood are shown in blue.

Okay, let's move on to dig a bit deeper into the structure of the heart and how blood flows through it and the names of the different chambers.

So here we've got our picture of the heart, and it's often drawn this way as kind of a cross section.

It's actually a little bit more complicated than this if you dissect a heart perhaps in science.

But the top two chambers are called the atria, also known as the left and right atrium.

And remember, and you can see there that the left atrium is actually on the right hand side of the piece of paper and it's the red signalling that it's oxygenated blood, whereas the right side of the heart is in a bluey colour because that's deoxygenated blood in that side, and that septum wall down the middle that divides them.

So blood enters the heart via the atria, it enters via the top of the heart and then it is pumped down into the bottom of the heart.

And the bottom two chambers are called ventricles.

So we have the left and right ventricles identified there.

And then the blood is ejected from the ventricles into the pulmonary and systemic circuit.

So then those bottom ventricles squeeze and that blood's ejected or squirted out into the arteries.

Let's do another quick check.

Which of the following chambers highlighted in red represents the left atrium? Think carefully.

Hopefully you got that one correct.

So the answer is B, and that left atrium is the top chamber that is actually on the right hand side when we look at the picture, but that's nearest to the left armpit.

As I mentioned earlier, the septum is that muscular wall down the middle of the heart.

And you may have heard of someone who suffers with a hole in the heart.

Well, that is actually, they've got a tiny hole in that septum that's allowing some of that oxygenated and deoxygenated blood to transfer back and forth.

So if you have a hole in the heart, often that leads to a need for surgery and certainly needing to be really careful if you're doing endurance events until that surgery has happened.

So it prevents that oxygenated blood from the left side from mixing with deoxygenated blood on the right side.

And then we also, alongside those chambers of the atria and the ventricles, we've got some really important valves in the heart.

And their job is to prevent the backflow of blood so that it keeps circulating in the right direction when our heart is contracting, when it's squeezing.

And interestingly, each heartbeat makes a budup sound.

That bud is the atrial contraction, so it's the atria contracting at the top of the heart.

And then there's a brief pause while those atrioventricular, or the tricuspid and bicuspid valves close off, stopping blood that's down in the ventricles from going back up into the atria when then those ventricles contract and that squeezes the blood forcibly out through the semilunar valves and into the arteries.

So if I run through that again, we've got the tricuspid valve on the right hand side of the heart, and the bicuspid valve on the left hand side of the heart.

And those are the two valves that are in between the atria and the ventricles.

And a nice way to remember that is that we try before we buy when we go shopping, don't we? And you can see when we look at it on the paper, the tricuspid is on the left hand side, bicuspid is on the right hand side.

So that's maybe one way that you can remember that, try before you buy.

And then we've got those semilunar valves, and they're the ones that close off once blood has been ejected up into the arteries to stop blood from coming back into the heart.

But instead it's gonna be refilling via the atria, via that venous return.

Okay, let's check.

Which of the following statements is incorrect? Is it A, valves in the heart prevent backflow of blood? Is it B, valves are between the atria and ventricles and on the exit of the heart into the main arteries? Is it C, valves prevent oxygenated and deoxygenated blood from mixing? Or is it D, valves in the heart are forced open due to increasing pressure? Remember, this question is asking which is incorrect.

I hope you selected C.

So preventing oxygenated and deoxygenated blood from mixing, that is in fact the septum, not the valves that achieves that.

And then let's do another check for understanding.

True or false? The tricuspid valve is between the atrium and the ventricle on the left side of the heart.

Have a think.

Is that true or false? It is false.

Okay, so although we try before we buy when we're reading it on paper, in fact, that tricuspid valve is between the right atrium and the right ventricle.

As you look at it on the paper, it's actually on the left hand side, and there's my top tip of remembering it because we try before we buy.

Okay, so blood first enters the heart from the lungs via the pulmonary vein.

So you can see that pipe going into the top left atrium through the pulmonary vein.

And then after it's gone through that left hand side of the heart, so the left atrium, down through the bicuspid valve into the left ventricle, it then goes out through the semilunar valve into the aorta, which is the largest artery of the human body.

And it will then branch off to all different body parts, a bit to your left arm, right arm, left leg, right leg, your abdomen, everywhere else except for the lungs.

And then meanwhile we've got deoxygenated blood that reenters the right hand side of the heart through the vena cava.

So that's the main vein of the human body.

And then after that blood has come in through the vena cava, it goes into the right atrium, down through the tricuspid valve, into the right ventricle, out through the semilunar valve into the pulmonary artery where it will then go back to the lungs for gaseous exchange to happen once again.

Let's do another quick check.

Which of the following returns deoxygenated blood from the body? Is it A, the pulmonary artery; B, the pulmonary vein; C, the aorta; or D, the vena cava? That's right.

It's D, the vena cava.

Okay, for this second task, I want you to fill the gaps and label this diagram to represent the pathway of oxygenated blood.

So we've got it there starting at number one, the lungs are where oxygen is collected.

So what is that vessel called that carries blood to the left atrium? Can you then add a label of where the left atrium is? Same for bicuspid valve.

Then where does it go, before you need to label up the semilunar valve, label up the aorta, and then label up that pipe way that goes to the body to deliver oxygen.

And then secondly, I want you to fill the gaps on this diagram that represents the pathway of deoxygenated blood.

And notice that I've ordered the list upside down to make it easier to not have so many crossovers of these labels, but the blood starting at the body at number nine, then which chamber does it go into, through a number of valves and the ventricles.

And then what is number 15 pointing towards, which is that main pipe that goes out to the lungs where oxygen is picked up again.

So pause the video now while you have a go at those two tasks, and come back to me when you are ready.

Okay, so here's what I'm hoping that you came up with.

We've got the lungs at the top there.

The pulmonary vein is carrying that blood back to the heart, into that top left atrium, through the bicuspid valve, into the left ventricle, up through the semilunar valve, into the aorta, and then off around to deliver oxygen to the body.

And then the second part of that task, we had the deoxygenated blood at the body coming back into the heart through the vena cava where it goes into the right atrium, through the tricuspid valve, into the right ventricle, then up through the semilunar valve, into the pulmonary artery, which takes that blood up to the lungs for oxygenating.

Okay, let's summarise what we've learned today about the double circulatory system and the structure of the heart.

So the heart operates as a double circulatory pump.

Deoxygenated blood travels from the right ventricle of the heart up to collect oxygen from the lungs, and then returns via the left atria into the heart.

And that is called the pulmonary circuit.

That oxygenated blood then travels into the aorta from the left ventricle to deliver oxygen to the working muscles of the body, and then it returns to the right atria.

And that is called the systemic circuit.

And then we also learned today that valves in the heart open due to that buildup of pressure, but then also close off to prevent backflow, because once the blood has travelled from the atria down into the ventricles, we don't want it going back up into the atria.

So those tricuspid and bicuspid valves close off, meaning that when the heart squeezes again, the blood is ejected out through the ventricles and out into the arteries.

Thanks for joining me today for this lesson.

I really look forward to seeing you again.

See you next time.