Lesson video

This lesson is human blood cells and blood vessels, 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 structures of blood and blood vessels and see how they are adapted to their functions.

Now during our lesson today, we're gonna come across a good number of keywords which has shown up on the screen now for you.

You may wish to pause the video and make a note of them now, but I will introduce them to you as we come across them.

Now in our lesson today, we are going to look firstly at what plasma and red blood cells are, and then we're gonna have a look at the blood vessels.

So hope you're ready to go.

I certainly am.

Let's get started.

So we know that the human circulatory system is a really important system within our body, and it contains blood, blood vessels, and the heart.

And the role of the circulatory system is to transport nutrients and waste products around our body.

It's also fundamental in our immune system, keeping our body safe from invading pathogens.

Now blood is one of the three significant components of the circulatory system and contains a number of different parts to it.

So the blood contains red blood cells, which is probably the first thing you would think of if you think of blood, you'd think of the red quality that blood has, and that's because of the red blood cells.

Now the red blood cells transport oxygen around our body from our lungs to all the various different cells within our body that require them.

White blood cells are also present within our blood and these are to responsible for fighting disease and keeping us safe from invading pathogens.

Blood also contains very, very small bits of cells called platelets, and these are primarily there to plug the holes in our blood vessels if we cut ourselves or if a blood vessel ruptures, and to encourage blood clotting so that we don't just bleed out.

And the blood clotting then forms scabs, and they heal and repair our blood vessels.

There's one other final part to our blood, and that's the plasma.

So the plasma is the liquid that these cells, the red, the white blood cells, and the platelets are suspended within.

And this fluid contains many other things besides.

Lots of things dissolved or suspended within it.

Some of which are nutrients and some of which are waste products.

And all of these things, including the cells, and these nutrients, and waste products are being transported around our body all of the time in the plasma via the circulatory system.

So what is plasma then? Well plasma, if we were to take out all of the cells from it, we would find it be to be a kind of yellowy liquid.

And in that, we would find all sorts of things dissolved or suspended within it because plasma is transporting nutrients such as glucose and other carbohydrates, amino acids, and proteins, lipids, minerals, and ions around our body.

And these are all fundamental in enabling us to grow and repair ourselves and also providing us with the energy that we need in order to undertake all the activities that we need to do as part of a living organism.

Also suspended within the plasma are the waste products.

So these are the things that we don't need anymore, and we need to get rid of.

These include things like carbon dioxide and urea, which is a form of nitrogenous compound, which is what makes our urine smell.

Also and largely in plasma is water.

And this is important to be moved around our body to the various different parts of it that is needed and also to keep our blood thin enough so that it can be moved.

And there are also many other substances which are dissolved or suspended within the plasma such as hormones, for instance, and antibodies as part of our immune system.

So there's lots and lots of things suspended within the plasma, and that's what makes it this kind of yellowy colour.

So let's just pause there for a moment and decide which of these three students of Laura, Izzy, and Alex correctly describe the role of plasma in the blood.

So Laura says, "Plasma causes blood to clot when we cut ourselves." Izzy says, "Plasma transports blood cells plus nutrients and waste products." And Alex says, "Plasma is a fluid which defends us against pathogens." But who is correct? I'll give you five seconds to think about it.

Okay, so hopefully, you've decided that Izzy is correct, well done.

Now we know that red blood cells are one of the things that are suspended within plasma, and red blood cells are really important.

This is what turns the plasma from yellow to our blood coloured red.

Now red blood cells transport oxygen from the lungs to all of the living cells within our body.

And this is really important because the oxygen is required for a process called cellular respiration, which happens in every living cell in our body.

And this is the process of converting energy from the stored form within our food into a form called ATP, which can then be used by the cells to enable various different functions to happen.

So cellular respiration is absolutely fundamental.

It's a really critical life process, and it requires oxygen to be most efficient.

And red blood cells transport that oxygen around our body.

So you can see that red blood cells are, therefore, most important as well.

Now red blood cells have a good number of adaptations to enable them to carry oxygen effectively around our body.

So let's consider them now.

The first thing is that they are absolutely stuffed to the gunwales with proteins called hemoglobins.

So haemoglobin is a protein that carries oxygen.

And it can carry oxygen because as part of the protein, it has iron ions, Fe2+ ions bound to it.

And it's to these iron ions that oxygen binds.

And because of the iron, the red blood cells are, therefore, able to carry oxygen around our body.

So this is why eating foods with iron in them such as red meats, green vegetables, those sorts of things, is really important to our diet because it's really important to have iron for our blood.

So that's the first adaptation.

Red blood cells do not, as a mature cell, have a nucleus.

They lose their nucleus as they grow up, essentially, as they mature.

And this means that there's even more space for the haemoglobin to be stacked and stuffed into the red blood cells.

So there's even more space to carry oxygen than there would be if there were a nucleus.

And finally, red blood cells have what is called a biconcave shape.

So if you imagine a donut where it's got that kind of depression in the middle, it's a bit like that.

There's not a hole going all the way through the middle of the red blood cell, but it is depressed, sunken in in the middle.

And we call this biconcave because a concave shape is a C shape, and biconcave is where there's two Cs sort of back to back, and where they bend into each other.

I don't know if you can see that with my fingers.

And that biconcave shape is really important to the shape of the red blood cell because it increases the surface area of the red blood cell, which means that oxygen can diffuse into the cell much more readily.

If it wasn't biconcave, then it would take much longer for the oxygen to diffuse into the red blood cell.

And this would be a problem because we wouldn't get as much oxygen around our body and to our living cells.

So we've got these three adaptations, which are really important to the function of the red blood cell.

The fact that they carry so many haemoglobin proteins, the fact that they have no nucleus.

So there's lots of space for even more haemoglobin molecules and the fact that they have this biconcave shape, which allows them to have a greater surface area over which oxygen can diffuse into and out of the cell.

So let's just reflect upon that then.

Which of these are adaptations of red blood cells for carrying oxygen? Is it a biconcave shape, a small surface area, a nucleus or haemoglobin? I'll give you five seconds to think about it.

Okay, so hopefully, you've remembered that the adaptations of red blood cells include the biconcave shape and the presence of lots of haemoglobin.

Well done if you got those right.

And also pause on this.

Which row in the table shows how red blood cells are adapted to their function? So do they have a nucleus? Is their surface area low or high? And how fast is the rate of diffusion, slow or fast? Put those together and choose the row which best describes their adaptations.

Okay, so red blood cells do not have a nucleus.

So we can rule out rows a and c straight away.

They have a high surface area, which rules out row b, and they have a fast rate of diffusion.

So that means the correct row describing red blood cells is row d.

Did you get that right? Well done if you did.

So what I'd like you to do now is to firstly draw a diagram of a red blood cell and add labels to show the three main adaptations of the red blood cell.

Then I'd like you to explain why each feature increases its ability to carry oxygen.

So the three labels that you need to add are the fact that there's haemoglobin, there's no nucleus, and there's a biconcave shape.

And then explain why they are really important to the red blood cell.

Now the diagram doesn't need to be anything fancy.

It just needs to be an outline shape of the red blood cell.

But do make sure that you get that kind of biconcave shape well-drawn.

Once you've done that, what I'd like you to do is to consider this scenario, that patients who have iron deficiency anaemia, their haemoglobin has less iron ions.

So explain then why this is likely to result in tiredness.

You may need to go back to other notes to help you answer that question.

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

Okay, let's review your work then.

So firstly, I asked you to draw a diagram and then explain why each feature increases its ability of a red blood cell to carry oxygen.

So your diagram really should be very straightforward.

So here's an example with biconcave shape and showing that it is a circular object.

Then you should have labelled the three parts, haemoglobin and explained why this feature increases its ability to carry oxygen.

Haemoglobin binds oxygen using Fe2+ or iron ions.

You also should have labelled the fact that there is no nucleus, which means that there is more space for haemoglobin and also identified the biconcave shape, which means that there's an increased surface area, so therefore an increased rate of diffusion of oxygen.

So just check your diagram over.

Is it clear enough? Doesn't need to be anything fancy and artistic or anything.

Just an outline will be fine with those three key features listed and explained.

Well done.

Then I asked you about patients with iron deficiency anaemia.

Now with patients with this condition, their haemoglobin has less iron ions.

So why will this result in tiredness? Well, your response should include ideas along the lines that haemoglobin carries oxygen, and the oxygen binds to the iron ions in the haemoglobin.

So if there is less iron in the haemoglobin, then less oxygen can be carried to other cells.

And this means that they will have less oxygen, and so less aerobic respiration can take place.

This means that less energy will be provided by respiration and this means that that will result in tiredness.

So check your answer over.

Did you get all of those really important points? Add to your work if you need to.

And well done for trying.

That was quite a challenging question.

Okay, let's move on to the next section of our lesson now, which is about blood vessels.

So we know what blood is and what it contains, and we know that blood moves around the body through blood vessels.

It doesn't just sort of slosh around our body any old how.

It goes through blood vessels.

There are three types of blood vessels.

Arteries, which take blood away from the heart.

You can think of A and A, arteries, away.

Veins take blood towards the heart.

And you can think of V and two Vs.

So V, veins and two Vs make a W to help you remember that perhaps.

So veins return blood towards the heart.

And capillaries are where the nutrients and the waste products exchange across the boundary between the blood vessel and the tissue.

So the nutrients can leave and the waste products can come back into the bloodstream.

So these are the three blood vessels.

Arteries, veins, and capillaries.

Now each of these vessels is highly adapted to its function.

So let's have a look at that now.

So arteries, as I've said, transport blood away from the heart.

Arteries away, okay? Think about that.

So in order to transport blood away from the heart and, therefore, towards all of the cells within the body, they have a thick, muscular and elastic wall, which can contract and relax rhythmically in time with a heart and also withstand the high pressure that the blood is being transported at.

So the blood needs to be maintained at a high pressure in order to get down to all the nooks and crannies within our body like our toes and our fingertips, and all of the ins and outs of all the organs within our body.

And in order to do that, to maintain that high blood pressure and also withstand the high blood pressure, the wall of the artery has to be thick, and muscular, and being slightly elastic, and muscular as well.

It can contract and relax and pump the blood around our body.

So when we are feeling for a pulse, what we're doing is feeling the contraction and relaxing of the muscle wall of the artery.

And that happens to be at the same speed at the same time as the heart pumps itself.

Now because of the thick wall, they have a narrow lumen.

So the lumen is just a fancy term for the hole in the middle, the bit that the blood flows through itself.

And the lumen being narrow means that the blood is kept at a high pressure.

So these two things are not exclusive.

The fact that there's a narrow lumen and a thick muscular elastic wall kind of go together.

The very fact that there is an a thick wall means that there's a narrow lumen as well.

And these are two really important features of the artery that helps the artery to take blood to all of the different parts of our body.

So the blood has got to all of our different parts of our body and it has to come back towards the heart again.

And that job is done by the veins.

Now the veins have a number of adaptations.

Their wall is thinner.

It does have some elasticity and muscularity to it.

So there is some muscle and elastic tissue within the wall of the vein, but there's much less of it.

And therefore, the wall is much thinner.

Now that means that the lumen, the hole in the middle can be much, much wider, and, therefore, the blood is transported at a much lower pressure 'cause it just needs to get back to the heart.

Doesn't need to get to all of the sections of the body 'cause that's where it's coming back from.

So because the blood is transported at lower pressure, the walls of the veins can be thinner because they don't need to withstand such high pressures, and they need to be a little bit elastic and a little bit muscular, but not very much 'cause they're not contracting and relaxing like the arteries are.

They're not pumping blood actively.

There's one other adaptation as well, and that's present within very long veins such as the ones running up the back of your leg.

And that's the presence of valves.

So veins have valves.

You can also remember that two Vs.

V, V, veins valves.

And the valves in veins, particularly long veins like the ones coming up the back of your leg just stop backflow of the blood, preventing it from just pooling in your feet.

It instead carries the blood up the body and prevents it from going the wrong way.

And that's really important because especially if you're standing for a very long time, we need to make sure that the blood is coming back to the heart so it can then be pumped back around the body again.

If it all just kind of collected within our feet, that wouldn't be very useful at all.

And you can see that actually the effect of that happening, people who have been stood up for a very, very long time, usually very, very still as well.

So if you think about soldiers standing on parade, for instance, sometimes, you'll see a soldier faint, and that's because their blood, they've been stood for such a long time that their blood is collecting in their lower parts of their body and not being able to be pumped around the body effectively.

And this means that they don't have enough blood to their brain and so they faint.

And then capillaries, we've said this is where nutrients are exchanged and waste products are exchanged between the blood itself and the tissues, the cells and the tissues.

So in order to do this, the capillaries must have a very thin wall.

So it is only one cell deep, and those cells have been flattened out, a bit like they've had a rolling pin over them.

So they're very, very thin, flat cells.

And that means there's a very short distance over which the nutrients and the waste products need to diffuse or exchange over.

And that means that diffusion and that exchange can happen extremely quickly.

So that's one adaptation.

The other significant adaptation of capillaries is that they have a very, very narrow lumen, barely one red blood cell wide.

And this means that the red blood cells are slowed right down and forced into single file, one by one by one.

And this means that they pass very slowly, at least comparatively very slowly, and that increases, therefore, the amount of time available for the exchange of nutrients and waste products to happen between the blood and the tissue cells.

So capillaries have these really interesting variations, this very thin flattened cell wall and this very, very narrow lumen, which makes the red blood cells really slow down and take their time as they're passing to allow for maximum diffusion and exchange of nutrients and waste products.

So let's just check ourselves on that then.

You've heard about the adaptations that arteries, veins and capillaries have, but which is which in this table? So in the table, there is the width of the wall, the width of the lumen.

Remember that's a hole in the middle, and where the valves are present.

So remember what I've just been talking to you about and try and work out which is the row for the artery, which is the road for the vein, and which is the row for the capillary.

And I'll stop and give you five seconds to think about that.

Okay, so hopefully, you've said that a thin wall with a wide lumen and the presence of valves means that that is the description of the vein.

The fact that the wall is one cell thick with a very narrow lumen with no valves means that that must be a capillary, and, therefore, a thick wall, a narrow lumen, but with no valves present must be an artery.

Did you get them all right in the correct order with the right decisions made? Well done if you did.

That's good job.

So what I'd like you to do now is to summarise the adaptations of blood vessels by completing the table.

So in the table you can see that there is listed the artery, the vein, and the capillary.

And what I'd like you to do is to summarise for each of those blood vessels the direction that the blood is travelling in, the adaptations that the vessel has, and the reasons why those adaptations are so important.

Now you don't need to write long sentences, just bullet points will be fine, but do make sure you get the correct adaptations with the correct blood vessels and list them all within the table.

Then I'd like you to consider the fact that blood in the arteries is moving at high pressure, whereas blood in the veins is moving at low pressure.

So can you use that information to explain why cutting an artery is going to be much, much more serious than cutting a vein? So consider what might happen, and why this is a significant issue.

So take your time when you are completing both of these tasks.

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

Okay, so let's mark our work then.

So the first task I asked you to complete the table to summarise the adaptations of the blood vessels.

So let's look at that.

So the arteries transport blood away from the heart.

And their adaptations include a thick, muscular, elastic wall and a narrow lumen.

And these are important adaptations because it means that they can contract in time with the heart and transport blood at high pressure.

For veins, the direction of blood is travelling towards the heart, and their adaptations are a thinner wall with a wide lumen and valves.

And the reason these are important is because the thinner walls and the wide lumen means that blood is at low pressure, and the valves prevent backflow.

For the capillaries, there's no direction of blood.

It's kind of between the two.

The adaptations are that the capillary has a wall, one cell thick, and a narrow lumen.

And this means that there is a short diffusion pathway and the narrow lumen slows the cells progress down, which means that there's more time for diffusion to take place.

So just review your work and see whether you've missed anything.

You may well have added a few extra notes in addition to these, which is great.

So don't rub anything out unless it's completely wrong, and well done if you have added some extra notes as well.

But make sure that you haven't missed any of these really important points as well.

Good stuff, well done.

Then I asked you to consider the fact that blood is transported at high pressure in arteries and low pressure in veins, and therefore, if we cut an artery, why is that much more serious than if we were to cut a vein? Well, hopefully we don't cut either, but this happens, accidents happen.

And what would be the result? Well, let's think about this then.

Your response might include things that if an artery is cut, you might have used the word severed instead because that's a kind of fancy word for cutting.

Then blood will pump out quickly and at high volume because it is at high pressure.

Whereas if you were to cut a vein or sever a vein, blood will pump out much more slowly and at a lower volume because the blood is at a lower pressure.

And this means, therefore, if you've cut, well, if you cut either, you'd have to press them firmly to prevent blood loss, significant blood loss.

But with an artery, the blood will kind of spurt out, really be thrusted and pumped out of the artery.

And so you'll have to press really firmly onto the artery to close it up and to stop significant blood loss.

So, I hope you've enjoyed our lesson today.

That's certainly given me quite a lot of food for thought anyway, and I hope it has for you too.

So in our lesson today, we've seen that blood contains blood cells, which are suspended in a fluid called plasma.

And this plasma transports water, glucose, and other nutrients plus waste products such as carbon dioxide and urea around our body through the blood vessels.

Red blood cells transport oxygen and are highly adapted to carry as much oxygen as possible and the blood flows through blood vessels, which are highly adapted.

So arteries carry blood away from the heart under high pressure.

Veins carry blood towards the heart under low pressure and contain valves.

And capillaries allow for the exchange of substances between the cells and the blood.

So I hope you've enjoyed our lesson today.

Thank you very much for joining me, and I hope to see you again soon, bye.