This lesson is called microscopy of human blood cells and blood vessels, and is in the unit to 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.

I'm really looking forward to this lesson because it's a practical one, so I hope you are too.

Now, in our lesson today, we're going to use a light microscope to observe blood cells and blood vessels, which is why I'm so excited.

And in our lesson today, we're gonna come across a good number of keywords.

So, they're up on the screen now.

You might wish to make a note of them by pausing the video first, but I will introduce them to you as we come across them so you don't have to do that.

Now, in our lesson today, we're going to first of all get the light microscope set up.

Then we're going to observe blood cells and then blood vessels.

So, are you ready to go? I definitely am.

So let's get started.

Now, we know that all organisms are made of cells and most cells are far too small to see with the unaided eye.

So, we need to zoom in on them using a microscope, and in our case, a light microscope to observe the cells and some of their features.

Now, a microscope, a light microscope has various parts to it.

So, let's quickly remind ourselves of those.

There is the eyepiece lens at the very top.

That's the bit that we look through.

The objective lenses are the ones that we can switch between and underneath that is the stage where we put our specimen or our slide.

We also have a light source.

Most microscopes nowadays have an inbuilt light source and use electricity.

But back in the olden days we used to shine a lamp onto a mirror, a bit more fiddly.

And then we've also got the coarse focusing wheel and the fine focusing wheel.

Now, these might be separately on the microscope or they might be interweaved with themselves like as shown in the diagram there.

But you will have two focus wheels, one for coarsely focusing, making big changes, and one for very, very fine focusing, which just makes very small changes.

So, they're the various different parts of the light microscope and they all have different roles.

So, the eye piece lens is generally speaking at times 10 magnification lens.

And so it does a small amount of magnification but not a vast amount.

Now, the objective lens is there's three of them and they will have different magnifications, often times four, x10 and x40.

But that will vary and you might find different magnifications on your own microscope.

The stage is where we're putting the specimen to view.

And the light source helps to illuminate the specimen shine light through it and enable us to be able to see it.

The coarse focusing wheel, as I've said, adjusts the focus in large increments, whereas the fine focus wheel adjust the focus in small increments.

So, it depends how much you want to focus it, how much more you need to adjust it as to which wheel you use.

So, quick check of understanding then.

Which label or labels indicates a part of the light microscope responsible for making the image sharper and clearer? A, B, C, or D.

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

Okay, so making the image sharper and clearer, that will be the focusing wheel.

So, if you said D, well done.

What about this question then? Which label or labels indicate a part of the light microscope responsible for increasing the size of the image? A, B, C, or D? I'll give you five seconds to think about it.

Okay, so for increasing the size of the image, well you should have chosen A, the eyepiece lens and C, the objective lens.

Well done if you've got them both.

Now, you need to be able to use the microscope safely and correctly and there are a certain number of systems and processes that you need to be able to do to do that.

So, what I'd like you to do is watch the video to see how to use the microscope safely and correctly.

Okay, let's check our understanding of that then.

So, which of these methods is most appropriate for using a light microscope to view cells? I'll give you five seconds, but you'll need longer than that to read all of the statements.

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

Okay, so hopefully from that you've picked out that B is the correct answer, that we're starting with the lowest power objective lens always.

Always go back to the lowest power, especially when you've switched slides.

And then you are using the coarse focusing wheel to move the stage to bring the specimen into focus.

So, you need to get ready for the practical.

The first thing you'll need to do is to collect the light microscope and set it up on your desk carefully and safely following the instructions that you've been shown in the video.

Then, to make sure that you understand what it is that you you're doing with the microscope, I'd like you to label the diagram of the microscope to show the key parts.

Then complete the table to show what the function is of those parts of the microscope.

And then finally, I need you to write a method for using the light microscope, which includes those key safety guidelines.

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

Okay, let's check our work then.

So, firstly, you should have collected the light microscope and set it up on your desk nice and carefully and safely.

Then I wanted you to label the diagram of the microscope showing the key parts.

So, you should have added the labels to the eyepiece lens, the objective lenses, the stage, the light source, the coarse, and the fine focusing wheels.

Then I wanted you to complete the table to show the function of those parts.

So, you should have said that the eyepiece lens is a viewing lens with times 10 magnification.

The objective lenses are three different lenses with different magnification.

The stage is where the specimen or the slide is placed.

The coarse focusing wheel adjust the focus in larger increments, whereas the fine focusing wheel adjust the focus in smaller increments.

And finally, the light source illuminates the specimen so that we can see it so it can be observed.

So, just check your work, make sure you've got the correct functions for each of those parts.

Then I asked you to write a method for using the light microscope using the key safety guidelines.

So, you might have included that firstly, you need to select the lowest power objective lens, then place the slide or the specimen onto the stage.

Then you're gonna use the coarse focus wheel to move the stage closer to the objective lens whilst watching from the side.

So, this is just to move the stage up to its highest point without crashing into the objective lens and crushing the specimen and damaging the lens.

Then you use the coarse focusing wheel to focus the specimen whilst moving the stage away from the lens.

So, this means that the slide isn't gonna get crushed, neither is the objective lens gonna get damaged and we will be able to bring it into focus.

Then you can use the fine focusing wheel to focus more precisely if you need to.

And once you've got it focused at a lower power, you can try it on the next power objective lens and refocus in the same way.

Again, check your work over, make sure you've got the correct method written out before we move on.

Well done.

So, let's have a look at observing blood cells.

Now, let's make sure we understand what it is that we are observing before we get on to doing that.

So, human blood contains a number of different cells.

So, in the picture here we can see red blood cells, which are what are involved in transporting oxygen, and we can see a white blood cell which is used to fight disease and provide us with immunity with our immune system.

So, these are two cells that are visible down the light microscope that are found in the blood.

So, red blood cells are very easy to view down the light microscope.

They appear in huge numbers and they are a pale pink red colour.

You can see that the darkness of the red will vary depending on what kind of angle you are looking at the cell, but they're kind of pink or red.

They are roughly circular and they have a shaded or a different coloured sort of centre because of their biconcave shape.

They are reasonably small compared to white blood cells.

So, you can see white blood cells there in those blue, purpley blue dots.

So, they are smaller than white blood cells.

They're reasonably small cells and they're quite easy to spot.

There's plenty of them.

We can also view white blood cells using a light microscope and there's a few different ones here in this picture.

Now, these are less frequent, significantly less frequent than red blood cells and they often are stained a purple or blue colour.

They are usually quite circular, but they do have irregularly shaped blobs inside because the nucleus, now that's the bit that stains purple or blue, the nucleus is often fragmented into smaller sections in a white blood cell and so you can see it's kind of broken up within the image.

You can also see that they are much, much larger than the red blood cells.

So, they're different colour and the different size makes them really quite easy to spot.

So, let's quickly check our understanding then.

Which of the following statements can be used to correctly describe a red blood cell when you viewed using a light microscope? Are they pale blue, are they circular, are they small? Do they have blobs? Do they have a shaded centre or are they large? So, which ones would you choose to correctly describe a red blood cell? I'll give you five seconds to think about it.

Okay, so you should have said that they are circular, that they are small, and that they have a shaded centre.

So, these are red blood cells.

Remember, it's the white blood cells which are pale blue with blobby nucleus and are much larger than the red blood cells.

So, well done if you picked out all three of those.

Now, when you are observing blood cells, it is possible to draw what you can observe, but you, when you are drawing using a light microscope, you must follow principles of biological drawings.

So, let's see what they involve.

Firstly, you mustn't be sketching or feathering your lines.

This is a scientific drawing.

It needs to be accurate and the cell membrane just doesn't have that kind of feathering and bits missing and overlapping and so on.

So, it would be inaccurate to draw it like that.

So, no feathering lines or sketching please.

You also shouldn't shade your diagram.

It might be really tempting to show that one bit is darker than the other, but that's not necessary in a biological drawing.

No shading please.

Now, we do need to label our diagram, but please do not add arrow heads to label lines.

It is unnecessary and it gets in the way of the diagram underneath, so no arrow heads, but instead please draw those label lines with a ruler and then add the correct labels alongside it.

As per this bottom diagram, that's a neatly drawn biological drawing diagram with no shading, no feathery lines, no sketching and no arrows, only straight lines that have been drawn for labelling.

We also need to include a scale on the drawing to show how much larger the object is compared to its actual size.

So, in order to do that, we're gonna add a scale using the magnification of the microscope that we were using when we were reviewing the image.

So, the total magnification of the microscope is the eyepiece lens magnification times by the objective lens magnification.

So, if the eyepiece lens has a magnification power of 10 and we've used the medium power objective lens, which also has a power of magnification power of 10, then we can say that the scale, the magnification, is times 100 and we can add that to our diagram.

So, quickly stop and check yourself with that.

Please calculate the total magnification for the following lenses and please do it for all of them.

So, pause the video and come back to me when you finish doing that.

Okay, let's quickly check our answers.

So, if the eyepiece lens has a magnification of times 10 and the objective lens is times four, then the total magnification is 10 times four, which is 40.

For part B, times 10 times 40 is times 400 magnification.

And for C, if we're using an eyepiece lens of times 15, but an objective lens of times 10, then we've got 15 times 10, which is 150.

Did you get those all correct? Make sure that you are multiplying them together rather than adding them.

Good stuff.

So, our final finished drawing will include neatly drawn biological diagrams with no shading or feathering, with label lines drawn with a ruler with no arrow heads and will include a title and a scale of magnification.

So, if we zoom in to the central part of the microscope image that we are looking at there on the right hand side, we can see the white blood cell and the red blood cell immediately above it.

I've drawn both of them and that's what you can see on the screen in my diagram that I've drawn and labelled.

That's the kind of thing that you are expecting to produce today.

So, let's just check our understanding.

Which of the following rules apply to micrograph drawings? So, is it that micrograph drawings have lines drawn with arrowheads? Is it that there is no shading? Is it that the lines are feathered or is it that labels are added? Which of the following rules apply? I'll give you five seconds to think about it.

Okay, so you should have said that lines drawn with arrow heads are not correct, but no shading is correct that the lines should not be feathered and that labels should be added.

Well done if you've got all of those correct.

So, what I'd like you to do now is to view a sample of blood using the light microscope and I want you to specifically identify the red and white blood cells that you can view.

Then choose one white blood cell and one red blood cell and carefully draw each of them using the rules for scientific drawings which are listed on the right of the screen.

Make sure you include a scale and a title.

Now, this is a really challenging task.

It's very difficult actually drawing down the microscope.

So, take your time and be really careful when you're doing it.

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

Okay, so let's have a look and see what you might have drawn.

So, firstly, you should have viewed a blood sample and spotted the red blood cells and the white blood cells.

Then you should have drawn one white blood cell and one red blood cell using the scientific drawing rules.

So, you should have drawn the white blood cell, just the outlines, remember no shading and a red blood cell as well, perhaps right next door to each other.

Then you should have added the scale.

So, in this case this is times 400 and then the title and in this case, this is red and white blood cells is viewed through a light microscope.

So, how accurate is your diagram? Have you shaded it? Have you feathered any of those lines? Have you made sure that they're all neatly joined? Have you labelled it correctly? Nothing that you can't see, but things that you can.

Have you included the scale and the title? Just check your work over a thorough and as I say, well done.

That's a really, really hard task to do actually and requires quite a lot of practise.

So, if you manage to get that well done in the first go, that's really quite impressive.

Good stuff.

Right, last thing I want to do is to look at blood vessels down the light microscope.

So, let's just check what we're gonna be looking at first before we go and view them.

So, we've just looked at blood and we know that this is flowing around our body through blood vessels including blood vessels such as the arteries which are taking blood away from the heart and veins which are returning blood back to the heart.

Now, we can observe these blood vessels using a light microscope and they're quite clear and big to see.

So, they're quite easy to observe.

And it's actually quite obvious the differences between the arteries and veins.

So, the image on the left is of an artery and you can see that they have a thick wall and a narrow lumen, whereas the image on the right is of a vein with a much thinner wall and a significantly wider lumen.

Remember, the word lumen is just about the hole in the middle through which the blood is flowing and you can really see quite significant differences in both the thickness of the wall between the arteries and the veins and the widths of the lumen, the narrow lumen in arteries and the wide lumen in veins.

So, that's the sort of thing that you are looking for, but why are there differences between arteries and veins? Why is there this physiological difference? So, arteries, remember they're transporting blood at high pressure so that they can get to all of the parts of the body that the blood needs to get to.

Remember, arteries are taking blood away from the heart and in order to do that, in order to get to all the various different parts of the body, it needs a thick wall, which is very muscular to be able to withstand the pressure of the blood at high pressure and a narrow lumen in order to keep that pressure high enough so that the blood actually gets there and doesn't just kind of stop flowing about halfway down our legs or something, that wouldn't be very good at all.

So, arteries have these features in order to keep blood at high pressure and withstand blood at high pressure.

What about veins then? Why are they different from arteries? Well, veins are returning blood back to the heart and this is happening at low pressure.

And in order, therefore, to cope with the blood at low pressure and return it back up to the heart, it needs not a significantly thick wall at all, quite a thin wall.

It needs a little bit of muscle but not a lot.

And it needs a really wide lumen, so that the blood can just flow, it can just get back to the heart.

It doesn't need to keep the blood at high pressure, it doesn't need to hurry it back there 'cause it's gonna get there anyway, 'cause of the way it's moving around the body.

It just needs to have a really wide vessel, a really wide lumen in order to carry that blood back to the heart.

And so the wall is thin and the lumen is wide.

So, which of the rows in the table correctly describe an artery and which one correctly describes a vein? So, we're looking at the direction of blood flow, the pressure of blood, the thickness of the wall, and the width of the looming in this table.

But one is for an artery, one is for a vein, and two are wrong.

Can you spot which is which? I'll give you five seconds to think about it.

Okay, so let's just go through this then.

So, direction of blood flow to the heart, so that's gonna be a vein, blood going back to the heart.

But the pressure of blood high, no, that's not right.

So, we can discount A straight away because that's incorrect for a vein.

Right, what about B then? So, B, the blood is going to the body, so it is gonna be at high pressure.

That's still correct.

It's going to have a thick wall, yes.

And a narrow lumen.

Yes.

So, this is an artery.

What about row C? So this is going to the body.

Well, we've already identified the artery so we can ignore that row and therefore by process of elimination, D should be the vein.

But let's just double check that first.

So, this is blood going back to the heart.

That is a vein.

Low pressure, yes, still also a vein.

With a thin wall, excellent.

And a wide lumen, yes, that's also a vein.

So, the bottom one is the vein.

So, just use that kind of process of elimination and rationalisation in order to help yourself with it, with a question like this.

And well done if you manage to identify both of those correctly.

Good stuff.

So, what I want you to do is now to get on and have a look using the light microscope at an artery and the vein.

Make sure you identify them correctly, that you've identified which one is the artery, which one is the vein.

You've got them around the right way, they're probably gonna be on the same slide.

Once you've done that, I want you to use your observations and the knowledge that you have of arteries and veins to explain why there are physical differences between these vessels and how this supports their function.

How the structure of the artery and the vein enables them to do what they have to do.

And then once you've finished that, have a go at making a scientific drawing of one or both of those vessels using the same drawing principles that we've used before when drawing the red and white blood cells.

So, don't include detail, just an overview of the structures and the appearance is enough so you don't need to be worrying about all the ins and outs and ins and outs of the cell membranes or the little speckles and dots and that kind of thing of the walls of the vessels.

But do remember to not use feathering or shading and any label lines that you draw must not have arrow heads, but be drawn with a ruler and add your scale and title two.

So, pause the video and come back to me when you're ready.

Okay, so hopefully when you are reviewing the artery and the vein, you identified them correctly.

So, on the left is the artery, on the right is the vein in this example.

Then I wanted you to explain why there are physical differences between these vessels and how this supports their function.

So, you should have said that arteries have a thick wall and a narrow lumen, and this keeps blood at high pressure so that it can reach all the parts of the body.

And the wall is muscular so that it can contract to help blood move around the body.

Whereas for veins, well they have a thinner wall and a much wider lumen.

And this is because blood is flowing at low pressure so that it can return to the heart.

Did you get all of those salient points? Make sure that you did in your explanation and well done.

And then finally, I asked you to make a scientific drawing of one or both of the vessels using the same drawing principles that we've used before.

So, your drawing for human artery, as I said, keep it really simple.

There's no need to put all of the ins and outs details and that's really, really hard to do.

So, just general outlines would've been fine.

And I've labelled the lumen, that's the hole in the middle and the artery wall, which is actually in two sections there according to the picture that I was viewing, I've added a title and I've added a scale of times 40.

This was at low power.

I've also drawn the vein, same principles, no shading or feathering.

And just the outlines, nice and simple with the lumen in the middle and the wall around the outside.

And again, added the title and the scale again at low magnification, so times 40.

Well done if you managed to get a scientific drawing done of those vessels.

Again, that's really, really hard.

It's really difficult to know what to include and what not to include.

So, hopefully you haven't included too much or even too little, but it's really hard.

It's a really quite a skill that needs to be built up over time.

So, well done for even having a go at that and that's great effort.

Well done.

Okay, so in our lesson today we've used the light microscope and we've seen that it has two lenses and two focus wheels, which help us to view specimens clearly and at high magnification.

We've viewed red and white blood cells using the light microscope and we've seen features of their cell structure that we can see using the microscope and drawing them.

We've had to go drawing them with using scientific techniques.

Now, we've seen that drawing scientifically means no feathering and shading, labelling lines drawn with a ruler with no arrow heads, and including a scale and title.

And we've practised that on a few occasions today.

And we've also seen an artery and a vein using the light microscope and there really is quite a clear difference in the thickness of the wall and the width of the lumen between these two blood vessels.

So, thank you very much for joining me again today.

I hope you've really enjoyed that lesson, I certainly have done.

Quite a challenge though, so well done and I hope to see you again soon.

Bye.