Lesson video

Hello and welcome to this lesson from the unit Stem Cells and Differentiation.

The title of today's lesson is Stem Cells in Animals.

We're gonna be looking at how our unspecialized cells become specialised cells, the types of cells that they become in animals, and how that process takes place.

My name's Mrs. Barnard, and I'm going to be taking you through today's lesson.

So by the end of today's lesson, you should be able to explain what stem cells are and give examples of where they are found in animals.

And we've got some keywords for today's lesson.

And our keywords are unspecialized cell embryo, embryonic stem cell differentiation and adult stem cell.

Now I'm gonna put a slide of the definitions up, so if you want to write them down, you can do, but otherwise we'll be going through them as we go throughout today's lesson.

So our lesson today is in two parts.

The first part of today's lesson is differentiation in embryos, and our second part of today's lesson is adult stem cells.

So let's get started with the first part of today's lesson differentiation in embryos.

So a little bit of a reminder for you that during sexual reproduction in humans, fertilisation produces a single cell, which we call a zygote.

And that's when our gametes come together and that a zygote that's formed is unspecialized.

It doesn't have a particular function, but it has the capability to become lots and lots of different types of cell.

So here we go, we've got our gamete, our sperm, and our egg, and together they form the zygote on fertilisation.

And then the zygote undergoes mitosis.

And our mitosis remember is when you have cell division where you make identical copies of the original cell.

So once it undergoes mitosis, an embryo forms. now when you get up to the stage of eight cells, all of those cells are actually unspecialized, okay? They have no particular function, but the capabilities become all types of cell.

Now we call these unspecialized cells, embryonic stem cells, as you can see this embryo to start with, and keeps undergoing mitosis until we get to this embryo of eight cells.

All unspecialized are all embryonic stem cells.

So these embryonic stem cells then have to undergo differentiation, and that's the process where you make all of the different types of specialised cells that are developing foetuses going to need.

So here are some examples.

So fat cells and muscle cells, epithelial cells.

So that one particularly is the ones that lie in the small intestine and neurons, which are our nerve cells.

So these are the examples of the cells that we'll need.

There's many more, but these are just a few.

So let's have a quick check.

Early embryonic cells are stem cells.

Now first of all, is that true or false? And then once you've decided, which of the statements below best justifies your answer.

So pause while you decide, and then when you come back, we'll see how you've got 'em.

Okay, so the answer to this one is true.

Early embryonic cells are stem cells and the best justification of this is the bottom one because they can differentiate into any type of cell.

So if you've got that right, then well done.

That's one of our keywords for today's lesson.

So during development, chemical changes in the embryo control, which genes are turned off and which genes are turned on, and that determines whether a protein is needed or not by the cell.

If it's not needed, then the gene for that particular protein that codes for that particular protein is turned off.

So we can see an example here in our model.

We've got our DNA, we've got some noncoding DNA in there, but we've got two genes as examples.

One of them is turned off, so therefore the protein is not produced and one of them is turned on.

That's what will make one cell different from another.

So the pattern of which genes are turned on and which genes are turned off in each specialised cells controls differentiation.

So those cells becoming different and this will lead to the presence of different proteins in different cells, and therefore they are no longer stem cells.

They have become specialised cells.

And here's an example in these pictures here that are down a microscope.

So this is an embryonic stem cell and then it undergoes differentiation.

So the expression of certain genes, and in this case it's becoming an epithelial cell in the trachea, your airways, and then it will undergo mitosis.

And if you remember, mitosis means it's gonna make identical copies of the cell that it originates from.

So we're gonna get lots of these epithelial cells in the trachea that make up the tissue lining the trachea.

Those little hairs on the surface are for wafting away our mucus in any dirt or bacteria that get into our lungs.

So it's really important, they have a really important job and they're really specialised to do so.

So embryonic stem cells can differentiate into any type of cell, but once they have become specialised and form tissues, they can't then become other types of cells.

They can't become unspecialized and they can't form other types of cells.

Again, here are some examples of the types of cells looking down a microscope this time of what a foetus would require.

So we've got cardiac muscles, that's the muscle that makes up your heart, the tissue of your heart.

We've got red blood cells that are obviously in your blood.

We've got again the epithelial cells that make up the tissue that lines the surface of your skin.

And then we've got nervous tissue, so nerves that make up the spinal cord.

So loads of different types of cells that have different gene expression.

So time for a quick check.

Select the processes that take place in the embryo to form a foetus.

So pause while you decide and then we'll check back to see if you've got it right.

Okay, let's have a look.

So the processes that take place in an embryo to form a foetus.

So we have got differentiation, that's those cells becoming different from one another through differential gene expression.

We've got mitosis, so those cells dividing in order to form tissues of the same cell.

So if you've got those right, then well done.

So it's time for a practise task now.

We've got a confidence grid here.

So for each and one of these statements, I want you to decide what you think it's correct, but are you sure it's correct or do you think it's correct? And are you sure it's incorrect or do you think it's incorrect? So select one tick for each statement.

So pause while you do that and then we'll come back and we'll look at the correct answers.

Okay, so let's go through these then.

So early embryonic cells can differentiate into any type of cell.

Okay, so this is correct.

They can differentiate to any type.

Specialised cells cannot change back into stem cells.

This is also correct, they can't.

All genes are turned on in all cells.

This is incorrect because that's what leads to a cell being specialised.

And finally, specialised cells divide by mitosis to form organs.

That one is incorrect.

They divide by mitosis to form tissues and then different tissues form organs.

So if you've got those right, then well done.

So time for part two.

So for each statement, I would like you to write an explanation to show your understanding.

Now some of the examples that I just talked through maybe will help you with that.

So pause while you do this 'cause a little bit of writing and then we'll come back and I'll give you some feedback.

Okay, so let's see how we got on with each of these statements then.

So for the first one, early embryonic cells can differentiate into any type of cell.

We can say they're formed by mitosis in the zygote and haven't differentiated.

Or you could say maybe all of their genes are turned off or something like that.

Specialised cells cannot change back into stem cells.

So once embryonic stem cells have differentiated, they can't go back to being stem cells.

All genes are turned on in all cells.

We need to correct that and we need to say specialised cells have some genes turned off and some genes turned on.

And that happens during differentiation.

And the final one, that one was incorrect as well.

So we need to change that.

So specialised cells divide by mitosis to form tissues.

So if you got those statements right or you wrote something similar that showed your understanding, then well done.

So it's time to move on to the second part of our lesson, which is adult stem cells.

So most embryonic stem cells will differentiate and become specialised.

However, some become adult stem cells.

So even though most cells from the embryo will become a specialised cell, there is just some that hang on and become adult stem cells.

However, these are slightly specialised because they are adult stem cells in particular regions of the body.

So unlike embryonic stem cells, adult stem cells differentiate into a limited number of specialised cells.

So for example, an adult blood stem cell can differentiate into specialised red blood cells, platelets, and different types of white blood cell.

So you can see that in this image here.

So we've got a stem cell there and it's differentiating, but the examples of the cells that it becomes are limited and specific to the region of the body that it is a stem cell for.

So adult stem cells are few in number compared to specialised cells, but they are found in the following regions of the body.

So we've got the brain, they're found in them making different neurons.

We've got the eyes making the different cells of the eyes, including photoreceptors.

We've got the skin making up the different layers of the surface of your skin.

We've got the blood, those cells we just looked at.

We've got the liver, we've got the heart and muscle, the different cells that make up your muscle fibres.

And we've got bone marrow, which is the living tissue that's within your bones, which is the living tissue, which is within your bone.

So they're in lots of different regions of the body.

So time for a quick check.

Adult stem cells can differentiate into any type of specialised cell.

Now do we think that's true or false? And when you've decided, can you choose which of the statements below best justifies your choice? So pause up while you decide and we'll come back and we'll see if you've got it right.

Okay, so the correct answer is false.

Adult stem cells can differentiate into any type of specialised cell that is false.

And the statement that best justifies that is only embryonic stem cells can differentiate into any type of specialised cell.

So if you got that right, then well done.

Let's move on.

So adult stem cells can differentiate into cells that are related to each other.

So here we go.

We've got an example.

So this is a human heart.

This is a photograph of a human heart, obviously outside of the body.

And to make that human heart, we need different types of cells.

It's not just made up of one type of cell.

So for example, we've got the smooth muscle cells.

So those ones that are types of cells that are controlled automatically, okay? And they will control processes within the heart or be within inside the vessels of the heart.

Then you've got your cardiac muscle that makes up the bulk of your heart.

That's the thing that causes the muscle contractions that allows your blood to be pumped around your body.

And then we've got this epithelial tissue.

We keep seeing this as an example, don't we? Because it is a tissue that is the lining tissue of most organs, including the surface of our skin, the lining of our small intestine, our airways, but also our heart.

So three different types.

These are all stained here to look down a microscope so we can see them more easily.

You can see the nucleus in each of them, but you can also see that the cells have got shapes.

So adult stem cells can divide by mitosis as well as differentiate because if they're only differentiated then we would run out of them.

So it's important that they also divide by mitosis.

So we've got a supply of those adult stem cells when we need them to differentiate into other types of cell.

So we've got a little image here to show you what it means.

We've got a stem cell here, an adult skin stem cell.

So it's gonna do two things.

It's gonna do self-renewal by mitosis to make sure that we've got plenty of cells there for the future.

And then it's also going to differentiate into these cells.

So different types of tissues in these pictures here.

So we've got those epithelial cells again, okay, those are gonna be on the surface of the skin.

Then we've got smooth muscle, which is gonna be underneath and in blood vessels.

And then we've got fat tissue layers.

So that helps to insulate us.

So these are just a few.

There are other different layers of skin, but these are just three different examples.

And you can see a cross section of the skin there.

You see it's quite a complicated organ.

It's made up of all sorts of different types of tissue and cells.

So bone marrow, adult stem cells are located in the bone.

So lots of people don't know this, but your bones aren't just solid.

They've got this living tissue that runs down the middle of them and in there is lots of different cells but also cells that make up our blood.

So it's where they are developed and produced.

So bone marrow contains stem cells that can differentiate it into many types of cells, including blood cells.

So you can see in this image here, different cells in inside the bone marrow.

So we've got our stem cells there.

We've also got some red blood cells or the precursors to red blood cells.

We've got different types of white blood cells 'cause there's not just one type of white blood cell.

There's lots.

We've got fat cells in there.

You can see that those are quite big because they're storing our fat.

So this is just a model of bone marrow tissue, but you can see all of the different cells that those bone marrow cells are going to differentiate into.

So also adult stem cells are located in the brain, and they can differentiate into different types of neurons.

We've got a couple examples here, a motor neuron.

So that's the type of neuron that sends information to your muscles and glands.

And we've got these Purkinje cells.

So they're in the surface of the brain, the cortex of the brain, that's to do with our senses.

And you can see that those look quite different shapes from each other.

That Purkinje one looks a little bit like an alien or an octopus, which looks quite different to the motor neuron on the other side.

So time for a quick check.

So choose examples of types of adult stem cells.

So pause while you decide and then we'll come back and we'll see if you've got it right.

Okay, so let's see if we've got this right.

So choose examples of types of adult stem cells.

So we have got brain, so if you've got the one on that's right, bone marrow and skin, so not embryo 'cause our embryonic stem cells are separate because they can differentiate into any type of cell.

Whereas our adult stem cells can only differentiate into small numbers of cells.

So another check here is for some key terms this time.

So we need to complete these sentences.

Adult stem cells can what into related types of cells.

And the second sentence, adult stem cells can renew themselves, they divide by what? So again, pause while you decide the correct answer and then we will see if you've got it right.

Okay then so adult stem cells can differentiate into related types of cells and adult stem cells can renew themselves.

They divide by mitosis.

So if you've got those right, then well done.

So now it's time for our practise task.

So Izzy has carried out some research into muscle stem cells and she has found out where they are located and what they differentiate into.

She will complete this diagram with the information from her research and use it to help explain what adult stem cells are.

So this is a bit of an open task for you this time.

What I would like you to do is carry out some research.

So you might use computer or information provided to you into a type of human adult stem cell and complete this task in the same way as Izzy.

So we need to see that those cells can self renew by mitosis, but what kind of cells are they differentiating into? So if you remember on a slide previously, there is a picture of all of the different parts of the body where you can find stem cells.

So you might want to select one of those or you might want to look at them all in general in your research and find the one that you find the easiest to explain okay? So pause while you do this, I mean this might take you a bit of time, but when you come back I'll give you some feedback on this specific example that Izzy has looked into to give you a more good answer.

Okay, let's see how you got with that research.

I hope you enjoyed it and you found out lots of information that you didn't already know.

So remember this is an example from Izzy.

So you might have done this one or you might have done something different.

So complete the diagram with the information from your research and use it to help explain what adult stem cells are.

So we've got Izzy's example, muscle stem cells.

So mitosis again for self-renewal, we've got it labelled adult muscle stem cell.

Then we've got differentiation labelled.

And then these are how the cells differentiate in muscles.

So they form myoblast cells and then they form muscle cells and their scientific name is myocytes.

And then those myocytes will form a myofibril, which is a muscle fibre.

And obviously those muscle fibres come together to form our muscles.

So you might have found the same for your example too or something different.

And we're using it to explain what adult stem cells are.

So we need an explanation underneath our diagram.

So something along the lines of adult stem cells are in some regions of the body such as muscles in this example.

They can renew themselves by dividing by mitosis and the adult stem cells can differentiate into a limited number of related cells.

So again, if you wrote something to that effect, then well done.

So time for us to come to the summary of today's lesson.

So here we go.

An early animal embryo is made of unspecialized cells.

These are called embryonic stem cells.

Embryonic stem cells can differentiate to become all types of cells in the animal's body.

Once specialised, they cannot return to being stem cells.

As an animal develops into an adult, some cells remain unspecialized.

And these are adult stem cells.

Adult stem cells can differentiate to become most, but not all types of cells in an animal's body.

Stem cells can renew themselves by dividing through the process of mitosis.

And finally, there are adult stem cells in different regions of the human body, e.

g.

, in the bone marrow.

And these can divide and differentiate to make blood cells.

So well done for your work in today's lesson.

And we will see you soon.