Lesson video

This lesson is called the human heart and double circulatory system.

And is from the Unit: Transport and exchange surfaces in humans.

Hi there, my name's Mrs. McCready, and I'm here to guide you through today's lesson so thank you very much for joining me.

In our lesson today, we're going to describe the function and the structure of the human heart and the importance of having a double circulatory system.

Now, we're gonna come across a number of keywords in our lesson today and they're noted up on the screen for you now.

You may wish to pause the video to make a note of them.

But I will introduce them to you as we come across them.

Now in our lesson today, we're going to first of all look at the function of the heart and then we're going to have a look at the structure of the heart.

So I hope you're ready to go.

I certainly am.

Let's get started.

So I hope you know that the human body is made up of billions of cells.

And every single one of those living cells undergoes a process called cellular respiration.

And in order to do that, in order to undergo cellular respiration, the cell requires nutrients and produces waste products.

So when we're talking about nutrients, we're talking about things like carbohydrates, and proteins and oxygen.

And when we're talking about waste products, we mean things like carbon dioxide and nitrogenous waste items, which are coming from proteins.

So every single cell requires nutrients in various forms and also makes many different waste products.

Now the circulatory system is really important because it transports those nutrients and waste products around the body within the bloodstream.

So the circulatory system transports nutrients to cells and waste products away from cells.

So nutrients which we have obtained through eating in our digestive system are transported from the digestive system to our living cells.

And oxygen that we have inhaled is transported from the lungs to our living cells.

Now the cells make carbon dioxide as a waste product, so that is transported from the cells back to the lungs so that it can be exhaled.

And nitrogenous waste which is made within the cells is then transported to the kidneys so that that can be excreted as well.

All of these transportations are happening via the circulatory system.

So the circulatory system includes three major parts.

It firstly includes the blood, which is what the waste products and the nutrients are all dissolved or suspended within.

It also includes the blood vessels, which is what the blood flows through, and the blood vessels permeate all different of our body so that blood can get to every single cell within our body.

And it also includes the heart.

Now the heart is an organ which pumps blood through the blood vessels, and that is a really important function which is what we're gonna be looking at in our lesson today.

So when we look at the heart, we can see that it is made up of specialised tissue called cardiac muscle.

And cardiac muscle is highly adapted to it's function because these cells can contract and relax together as a unit and rhythmically to produce the pumping function of the heart.

And it's because these cardiac muscle cells contract and relax rhythmically, and together in unison that blood can be moved around the body.

So let's have a quick check.

Is the heart a tissue, an organ, or an organ system? I'll give you five seconds to decide.

Okay, so hopefully you've remembered that the heart is an organ which is made up of many different specialised tissues.

And is part of the organ system, the circulator system.

Well done.

I'd also like you to think about this, cardiac muscle cells contract and relax rhythmically.

Is that true or false? I'll give you a few seconds to think about that.

So hopefully you've remembered that that is true, but can you justify your answer with one of the two statements here.

That either this pumps blood around the body through blood vessels or that this pumps blood around the cells of the body.

Which is correct? So hopefully you've said that cardiac muscle cells contract and relax rhythmically because this pumps blood around the body through the blood vessels.

Well done, if you're getting both of those right.

So what I'd like you to do now is to choose one nutrient and one waste product.

Then for each of them, I would like you to describe what the substance starts its journey and where the substances moved to by the end of its journey.

And then for both of them together, in one sentence I'd like you to describe how the substance is moved from its start to finish locations.

Once you've done that, I'd like you to consider this, that the cardiac muscle cells contain about 5,000 mitochondria per cell.

So can you remember what the function of mitochondria are and suggest why each cell requires so many mitochondria? So take your time with both of these tasks.

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

Okay, so hopefully you've had a good go at both of these tasks so let's see what you might have done with them.

So for the first task where I wanted you to choose one nutrient and one waste product, and then describe where they start and where they finish.

And then also describe how the substances moved from its start and finish locations both of them.

You might have said two of the following, that oxygen is moved from the lungs to all cells, or that nutrients from food are moved from the digestive system to all cells, or that carbon dioxide is moved from cells to the lungs, or that nitrogenous waste is moved from cells to the kidneys.

And then you should have said in addition to that, for both of those substances, that these nutrients and waste products are transported around the body by the circulatory system.

So just review your response to that before we move on.

And then in response to our second task about cardiac muscle cells.

So they contain about 5,000 mitochondria per cell.

So why is it that each of those cells requires so many mitochondria? Can you remember what mitochondria do? Well, hopefully your response includes parts of this answer.

That firstly, that mitochondria produce ATP during cellular respiration.

And ATP stores energy for the cell.

Now, the cardiac muscle cells are continuously contracting and relaxing rhythmically to pump blood around the body, and this requires a lot of energy and therefore a lot of mitochondria.

Which is why cardiac muscle cells have so many mitochondria per cell.

So just check your answer over, add in anything that you might have missed.

And well done, that was quite a challenging question.

Okay, let's look at now the structure of the heart.

So the heart pumps blood to two locations.

It pumps blood to the lungs and it also pumps blood to the body.

So blood returns from the body to the heart and then goes from the heart to the lungs.

It is then transported back from the lungs to the heart and then is pumped again to the body.

So you can see here that the heart is pumping the blood twice, and this is why the human circulatory system is known as a double circulatory system because blood is passing through the heart twice.

Once when it goes to the lungs and a second time when it's pumped to the body.

Now the internal structure of the heart includes four chambers.

The right atrium, the right ventricle, the left atrium, and the left ventricle.

Now you may think that I've completely lost my mind here and I've put the right on the left and the left on the right.

But when we're looking at diagrams of the heart, what we're doing is looking at them as if we are looking at the heart in somebody's body where they're facing us.

And because they would be facing us, their right side is on our left and their left side is on our right.

So we always put the right side of the heart on the left side of the page, and the left side of the heart on the right side of the page.

So you just need to bear that in mind when you are labelling up the heart, it can be a little bit confusing, but you just need to remember that you are looking at it as if you've got somebody standing in front of you, facing forwards towards you, and you're looking at their heart and labelling it up from that perspective.

So these four chambers, there are two atria at the top of the heart and there are two ventricles at the bottom of the heart.

Now you can remember that really easily if you think about the capital letters A and V.

So the capital letter A joins at the top, so the atria are at the top of the heart.

And the ventricles, well, a V joins together at the bottom of the letter, and the ventricles are at the bottom of the heart.

So I hope that little memory trick helps you to remember that the atria at the top and the ventricles are at the bottom of the heart.

Now these chambers are really important because what they do is store blood temporarily and allows it to be built up to a higher pressure, which means it's going to go further and with certainty as it's pumped out of the heart.

Now the right-hand side of the heart deals with deoxygenated blood so this is blood which now has no oxygen left in it.

So deoxygenated blood returns from the body to the right side of the heart via the vena cava.

So the vena cava is the name of the vein through which this blood is moving.

And vena cava just means cavernous vein.

It is the largest vein in the body.

So blood is flowing through the vena cava into the heart from the body, and it enters the right atrium.

It then passes from the right atrium down to the right ventricle, and then it's pumped again up through the ventricle, out through the pulmonary artery to the lungs.

Now, pulmonary means of the lung.

So the pulmonary artery is a blood vessel which is taking blood to the lungs.

And because it's going away from the heart, it's an artery rather than a vein.

So the pulmonary artery is taking blood to the lungs.

So just quickly check yourself on that.

Starting with where deoxygenated blood first arrives, can you order these parts of the heart by the direction of blood flow? So I'll give you five seconds to think about that.

Okay, so you should have started that deoxygenated blood arrives via the vena cava and then moves into the right atrium.

From the right atrium, it is then pumped into the right ventricle before leaving the heart via the pulmonary artery.

So well done if you've got all of that correct.

So let's look at the left side now.

So the left side of the heart deals with oxygenated blood.

So this is blood returning from the lungs with oxygen bound to it.

So oxygenated blood is returning from the lungs via the pulmonary veins.

Remember, pulmonary just means of the lungs and veins are vessels that upbringing blood back to the heart.

So the pulmonary veins are transporting blood back to the heart and into the left atrium.

From there, blood is then pumped from the left atrium into the left ventricle, and then the left ventricle pumps the blood out of the ventricle through the aorta to the body.

And the aorta is just the largest artery in the body coming straight from the heart.

So let's check yourself again.

Starting with where oxygenated blood first arrives, can you order these parts of the heart by the direction of blood flow? I'll give you five seconds to think about it.

Okay, so hopefully you've started off with blood returning oxygenated from the lungs via the pulmonary vein and entering the left atrium.

From there, it is pumped into the left ventricle before leaving the heart via the aorta.

So well done if you've got all of those correct.

Now, deoxygenated blood and oxygenated blood has to be kept separate.

It would be really counterproductive if we mixed oxygenated and deoxygenated blood together.

So we know that deoxygenated blood is pumped through the right side of the heart, whereas the left side of the heart is dealing with oxygenated blood freshly from the lungs.

And there's a wall separating these two sides of the heart.

And this wall is called the septum.

And the septum separates the left and the right sides so that the oxygenated and the deoxygenated blood cannot be mixed up together.

So what I'd like you to do is match the part of the heart with its function.

So the parts of the heart include the heart chamber, cardiac muscle and the septum.

And the functions include separates oxygenated and deoxygenated blood.

Contracts force blood out of the chamber.

And stores blood temporarily to allow pressure to build up.

But which part matches with which function.

I'll give you five seconds to think about it.

Okay, so hopefully you've said that the heart chamber stores blood temporarily to allow pressure to build up.

That cardiac muscle contracts to force blood out of the chamber and the septum separates oxygenated and deoxygenated blood.

Did you get them all right? Well done if you did.

Now blood flows through the heart in one direction.

You've probably already seen that work that out.

But let's just review that so we are really clear in which direction that is.

So the blood starts in the vena cava.

This is the cavernous vein where it's come back to the heart from the body.

And from there it moves into the right atrium, then the right ventricle before it leaves the heart via the pulmonary artery and goes to the lungs.

Once it's picked up oxygen from the lungs, it then returns to the heart via the pulmonary vein.

Then it moves into the left atrium, then the left ventricle, before it leaves the heart via the aorta to go to the body.

And that just carries on and on and on.

Now the heart uses valves to ensure that blood moves through in the correct direction.

So we know that blood is moving from the atria to the ventricles.

And there is a valve which sits between these two chambers of the heart and they are called the atrioventricular valves.

So the atrioventricular valves sit between the atrium and the ventricles, hence their name, and they stop backflow of blood from the ventricles back into the atrium, which would be the wrong way of moving.

So valves are really important and make sure that blood is moving in the correct direction all of the time.

There's another set of valves as well which does similar thing and these are called the semilunar valves.

So the semilunar valves are.

Well, half-moon shaped in shape, which is where they get their name from, and they sit at the top of the ventricles and stop blood from coming back into the ventricles once it's left via the arteries.

So the semilunar valves sit between the right ventricle and the pulmonary artery and the left ventricle and the aorta.

And again, it just stops blood from moving backwards through the heart the wrong direction.

So the ventricles, as you may remember, pump blood out of the heart via the arteries.

So the right ventricle pumps blood out of the pulmonary artery to the lungs and the left ventricle pumps blood out of the aorta to the body.

Now there's an interesting pressure difference between the blood that is pumped out of the different sides of the heart.

So on the right side, the blood leaving the right ventricle leaves at a low pressure to go to the lungs.

And this is because if it were at high pressure, it would damage the lungs and cause us death.

The left ventricle, however, has to pump blood to all of the body.

That means up to the top of our head and all the way down to our toes and everything in between, including all of the organs inside the abdomen of our main body.

And because it's got to reach blood to all of these much further away, and in some cases, against gravity such as our head, parts of our body, it therefore has to pump blood at much higher pressure.

And because it has to pump blood at higher pressure, the left ventricle wall is much thicker and that is because it has to produce much greater force on the blood to pump it to all the various different sections of our body rather than just to the lungs.

You can see there in the diagram that the left ventricle wall is substantially thicker, two to three times thicker than the right ventricle wall because of this.

So let's just quickly check ourselves on that.

The right ventricle wall is thicker than the left ventricle wall.

True or false? Well, hopefully you've said that that is false, but can you justify your answer? So is it that more force required to pump blood to the body or is it because more force is required to pump blood to the lungs, which is correct? I'll give you a few seconds to think about it.

So hopefully you said that that is false because more force is required to pump blood to the body.

Well done, if you got that right.

And what about this, which letter shows how backflow of blood is prevented? So hopefully, you've decided that it is section D that's pointing to the atrioventricular valve on the left side of the heart.

Well done, if you got that right.

So what I'd like you to do now is to summarise your learning in a detailed way.

Firstly, by adding the following labels to the heart diagram.

So the four different blood vessels, the vena cava, the aorta, the pulmonary artery, and the pulmonary vein.

The two atria on the right and left sides.

The two ventricles on the right and left side.

The two sets of valves, the atrioventricular and the semilunar and the septum.

Then can you create a flow chart to show how blood moves through the parts of the heart, the body and the lungs in the correct order.

And then finally, can you explain why the heart has a septum and valves? Now, take your time over this.

Really check your work, make sure you've got the various different parts of the heart laboured up properly and you've got them sequenced correctly as well.

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

Okay, let's check our work then.

So firstly, I asked you to add labels to the heart diagram.

So you should have included the vena cava on the top left of the diagram, then the aorta moving clockwise round, then the pulmonary artery next, and then the pulmonary vein.

So they're the four main vessels coming to or from the heart.

Then you should have added the atrium, the right atrium on the left side of the heart and the left atrium on the right side of the heart.

And then the ventricles, the right ventricle on the left side, the left ventricle on the right side at the bottom of the heart.

Then the valves, so the atrioventricular valves being indicated between the atria and the ventricles.

And the semilunar valves sitting between the ventricles and the arteries that are leaving the heart so the pulmonary artery and the aorta.

And then finally the septum, which sits between the right side and the left and keeps that oxygenated and deoxygenated blood separate.

So check that you've got everything labelled in the right locations and make any amendments if you need to.

Well done.

So let's have a look at the flowchart then to show how blood is moving through the heart, the body and the lungs.

So hopefully, you've started off at the vena cava, which is where blood returns from the body into the heart through.

Then put the right atrium, then the right ventricle, then the pulmonary artery to the lungs.

And then when it's come back from the lungs, the blood enters the pulmonary vein to return to the left atrium.

Then the left ventricle then leaves the heart via the aorta to go to the body and then starts again.

So again, just check your flowchart, make sure that everything is in the correct location.

And make any amendments if you need to, to make sure that your work is correct.

Then finally, I asked you to explain why the heart has a septum and valves.

So your answer should have included that the right-side pumps deoxygenated blood from the body to the lungs, and the left side pumps oxygenated blood from the lungs to the body.

The septum divides the right and left sides of the heart, which keeps the deoxygenated and oxygenated blood separate.

Whereas the atrioventricular valves divide the atria and the ventricles.

And the semilunar valves divide the ventricles from the arteries.

And this means that they prevent backflow of blood and ensures that blood moves in the correct direction through the heart.

So again, that's quite a detailed response.

So just check your work over and make sure you've got all the really important points there.

And well done for making such a concerted effort in that, that was really quite challenging.

So let's just review our lesson.

So we've seen in our lesson today, that blood transports nutrients and waste products around the body in the circulatory system.

And it is pumped around the body by an organ called the heart.

Now the heart is made up of cardiac muscle, which rhythmically contracts and relaxes to pump blood.

And it has four chambers, the right and left atria.

So the singular is atrium, the plural is atria.

And the right and left ventricles.

So the atria are at the top, and the ventricles are at the bottom.

Now these chambers are divided by valves which prevent the backflow of blood to make sure that the blood moves through the heart in the correct direction.

And the heart pumps deoxygenated blood to the lungs and then oxygenated blood to the body, in what is known as a double circulatory system.

So I hope you've learned masses in this lesson today and found it really interesting as well.

And I'd like to thank you very much for joining me today, and I hope to see you again soon.

Bye.