Embryonic Stem Cells

Where we left off after the
meiosis videos is that we had

two gametes.

We had a sperm and an egg.

Let me draw the sperm.

So you had the sperm and
then you had an egg.

Maybe I'll do the egg in
a different color.

That's the egg, and we all
know how this story goes.

The sperm fertilizes the egg.

And a whole cascade of events
start occurring.

The walls of the egg then become
impervious to other

sperm so that only one sperm can
get in, but that's not the

focus of this video.

The focus of this video is how
this fertilized egg develops

once it has become a zygote.

So after it's fertilized, you
remember from the meiosis

videos that each of these were
haploid, or that they had--

oh, I added an extra i there--
that they had half the

contingency of the DNA.

As soon as the sperm fertilizes
this egg, now, all

of a sudden, you have
a diploid zygote.

Let me do that.

So now let me pick
a nice color.

So now you're going to have a
diploid zygote that's going to

have a 2N complement of the DNA
material or kind of the

full complement of what a normal
cell in our human body

would have. So this is diploid,
and it's a zygote,

which is just a fancy way of
saying the fertilized egg.

And it's now ready
to essentially

turn into an organism.

So immediately after
fertilization, this zygote

starts experiencing cleavage.

It's experiencing mitosis,
that's the mechanism, but it

doesn't increase
a lot in size.

So this one right here will then
turn into-- it'll just

split up via mitosis
into two like that.

And, of course, these are each
2N, and then those are going

to split into four like that.

And each of these have the same
exact genetic complement

as that first zygote, and
it keeps splitting.

And this mass of cells, we can
start calling it, this right

here, this is referred
to as the morula.

And actually, it comes from the
word for mulberry because

it looks like a mulberry.

So actually, let me just kind
of simplify things a little

bit because we don't
have to start here.

So we start with a zygote.

This is a fertilized egg.

It just starts duplicating via
mitosis, and you end up with a

ball of cells.

It's often going to be a power
of two, because these cells,

at least in the initial stages
are all duplicating all at

once, and then you
have this morula.

Now, once the morula gets to
about 16 cells or so-- and

we're talking about
four or five days.

This isn't an exact process--
they started differentiating a

little bit, where the outer
cells-- and this kind of turns

into a sphere.

Let me make it a little
bit more sphere like.

So it starts differentiating
between-- let me make some

outer cells.

This would be a cross-section
of it.

It's really going to look
more like a sphere.

That's the outer cells and then
you have your inner cells

on the inside.

These outer cells are called
the trophoblasts.

Let me do it in a
different color.

Let me scroll over.

I don't want to go there.

And then the inner cells, and
this is kind of the crux of

what this video is all
about-- let me scroll

down a little bit.

The inner cells-- pick
a suitable color.

The inner cells right there are
called the embryoblast.

And then what's going to happen
is some fluid's going

to start filling in some
of this gap between the

embryoblast and the trophoblast,
so you're going

to start having some fluid that
comes in there, and so

the morula will eventually
look like this, where the

trophoblast, or the outer
membrane, is kind of this huge

sphere of cells.

And this is all happening as
they keep replicating.

Mitosis is the mechanism, so now
my trophoblast is going to

look like that, and then
my embryoblast is going

to look like this.

Sometimes the embryoblast-- so
this is the embryoblast.

Sometimes it's also called the
inner cell mass, so let me

write that.

And this is what's going to
turn into the organism.

And so, just so you know a
couple of the labels that are

involved here, if we're dealing
with a mammalian

organism, and we are mammals,
we call this thing that the

morula turned into is a zygote,
then a morula, then

the cells of the morula started
to differentiate into

the trophoblast, or kind of the
outside cells, and then

the embryoblast. And then you
have this space that forms

here, and this is just fluid,
and it's called the

blastocoel.

A very non-intuitive spelling
of the coel part of

blastocoel.

But once this is formed, this is
called a blastocyst. That's

the entire thing right here.

Let me scroll down
a little bit.

This whole thing is called the
blastocyst, and this is the

case in humans.

Now, it can be a very confusing
topic, because a lot

of times in a lot of books on
biology, you'll say, hey, you

go from the morula to
the blastula or the

blastosphere stage.

Let me write those words down.

So sometimes you'll say morula,

and you go to blastula.

Sometimes it's called
the blastosphere.

And I want to make it very
clear that these are

essentially the same stages
in development.

These are just for-- you know,
in a lot of books, they'll

start talking about frogs or
tadpoles or things like that,

and this applies to them.

While we're talking about
mammals, especially the ones

that are closely related
to us, the stage is the

blastocyst stage, and the real
differentiator is when people

talk about just blastula
and blastospheres.

There isn't necessarily this
differentiation between these

outermost cells and these
embryonic, or this

embryoblast, or this inner
cell mass here.

But since the focus of this
video is humans, and really

that's where I wanted to start
from, because that's what we

are and that's what's
interesting, we're going to

focus on the blastocyst.

Now, everything I've talked
about in this video, it was

really to get to this point,
because what we have here,

these little green cells that
I drew right here in the

blastocysts, this inner cell
mass, this is what will turn

into the organism.

And you say, OK, Sal, if that's
the organism, what's

all of these purple
cells out here?

This trophoblast out there?

That is going to turn into the
placenta, and I'll do a future

video where in a human, it'll
turn into a placenta.

So let me write that down.

It'll turn into the placenta.

And I'll do a whole future video
about I guess how babies

are born, and I actually learned
a ton about that this

past year because a baby
was born in our house.

But the placenta is really
kind of what the embryo

develops inside of, and it's the
interface, especially in

humans and in mammals, between
the developing fetus and its

mother, so it kind of is the
exchange mechanism that

separates their two systems,
but allows the necessary

functions to go on
between them.

But that's not the focus
of this video.

The focus of this video is the
fact that these cells, which

at this point are-- they've
differentiated themselves away

from the placenta cells, but
they still haven't decided

what they're going to become.

Maybe this cell and its
descendants eventually start

becoming part of the nervous
system, while these cells

right here might become muscle
tissue, while these cells

right here might become
the liver.

These cells right here are
called embryonic stem cells,

and probably the first time in
this video you're hearing a

term that you might recognize.

So if I were to just take one of
these cells, and actually,

just to introduce you to another
term, you know, we

have this zygote.

As soon as it starts dividing,
each of these cells are called

a blastomere.

And you're probably wondering,
Sal, why does this word blast

keep appearing in this kind
of embryology video, these

development videos?

And that comes from the Greek
for spore: blastos.

So the organism is beginning
to spore out or grow.

I won't go into the word origins
of it, but that's

where it comes from and that's
why everything has

this blast in it.

So these are blastomeres.

So when I talk what embryonic
stem cells, I'm talking about

the individual blastomeres
inside of this embryoblast or

inside of this inner
cell mass.

These words are actually
unusually fun to say.

So each of these is an
embryonic stem cell.

Let me write this down
in a vibrant color.

So each of these right here are
embryonic stem cells, and

I wanted to get to this.

And the reason why these are
interesting, and I think you

already know, is that there's
a huge debate around these.

One, these have the potential
to turn into anything, that

they have this plasticity.

That's another word that
you might hear.

Let me write that down,
too: plasticity.

And the word essentially comes
from, you know, like a plastic

can turn into anything else.

When we say that something has
plasticity, we're talking

about its potential
to turn into a lot

of different things.

So the theory is, and there's
already some trials that seem

to substantiate this, especially
in some lower

organisms, that, look, if you
have some damage at some point

in your body-- let me
draw a nerve cell.

Let me say I have a-- I won't
go into the actual mechanics

of a nerve cell, but let's say
that we have some damage at

some point on a nerve cell right
there, and because of

that, someone is paralyzed
or there's some nerve

dysfunction.

We're dealing with multiple
sclerosis or who knows what.

The idea is, look, we have these
cell here that could

turn into anything, and we're
just really understanding how

it knows what to turn into.

It really has to look at its
environment and say, hey, what

are the guys around me doing,
and maybe that's what helps

dictate what it does.

But the idea is you take these
things that could turn to

anything and you put them where
the damage is, you layer

them where the damage is, and
then they can turn into the

cell that they need
to turn into.

So in this case, they would
turn into nerve cells.

They would turn to nerve cells
and repair the damage and

maybe cure the paralysis
for that individual.

So it's a huge, exciting area
of research, and you could

even, in theory, grow
new organs.

If someone needs a kidney
transplant or a heart

transplant, maybe in the future,
we could take a colony

of these embryonic stem cells.

Maybe we can put them in some
type of other creature, or who

knows what, and we can turn it
into a replacement heart or a

replacement kidney.

So there's a huge amount
of excitement about

what these can do.

I mean, they could cure a lot of
formerly uncurable diseases

or provide hope for a
lot of patients who

might otherwise die.

But obviously, there's
a debate here.

And the debate all revolves
around the issue of if you

were to go in here and try to
extract one of these cells,

you're going to kill
this embryo.

You're going to kill this
developing embryo, and that

developing embryo had
the potential to

become a human being.

It's a potential that obviously
has to be in the

right environment, and it has
to have a willing mother and

all of the rest, but it does
have the potential.

And so for those, especially, I
think, in the pro-life camp,

who say, hey, anything that has
a potential to be a human

being, that is life and it
should not be killed.

So people on that side of the
camp, they're against the

destroying of this embryo.

I'm not making this video to
take either side to that

argument, but it's a potential
to turn to a human being.

It's a potential, right?

So obviously, there's a huge
amount of debate, but now, now

you know in this video what
people are talking about when

they say embryonic stem cells.

And obviously, the next question
is, hey, well, why

don't they just call them stem
cells as opposed to embryonic

stem cells?

And that's because in all of our
bodies, you do have what

are called somatic stem cells.

Let me write that down.

Somatic or adults stem cells.

And we all have them.

They're in our bone marrow to
help produce red blood cells,

other parts of our body, but the
problem with somatic stem

cells is they're not as plastic,
which means that they

can't form any type of cell
in the human body.

There's an area of research
where people are actually

maybe trying to make them more
plastic, and if they are able

to take these somatic stem
cells and make them more

plastic, it might maybe kill
the need to have these

embryonic stem cells, although
maybe if they do this too

good, maybe these will have
the potential to turn into

human beings as well,
so that could

become a debatable issue.

But right now, this isn't an
area of debate because, left

to their own devices, a somatic
stem cell or an adult

stem cell won't turn into
a human being, while an

embryonic one, if it is
implanted in a willing mother,

then, of course, it will turn
into a human being.

And I want to make one side
note here, because I don't

want to take any sides on the
debate of-- well, I mean,

facts are facts.

This does have the potential
to turn into a human being,

but it also has the potential
to save millions of lives.

Both of those statements are
facts, and then you can decide

on your own which side of that
argument you'd like to or what

side of that balance you
would like to kind of

put your own opinion.

But there's one thing I want
to talk about that in the

public debate is never
brought up.

So you have this notion of when
you-- to get an embryonic

stem cell line, and when I say
a stem cell line, I mean you

take a couple of stem cells, or
let's say you take one stem

cell, and then you put it in a
Petri dish, and then you allow

it to just duplicate.

So this one turns into two,
those two turn to four.

Then someone could take one of
these and then put it in their

own Petri dish.

These are a stem cell line.

They all came from one unique
embryonic stem cell or what

initially was a blastomere.

So that's what they call
a stem cell line.

So the debate obviously is when
you start an embryonic

stem cell line, you are
destroying an embryo.

But I want to make the point
here that embryos are being

destroyed in other processes,
and namely, in-vitro

fertilization.

And maybe this'll be my next
video: fertilization.

And this is just the notion that
they take a set of eggs

out of a mother.

It's usually a couple that's
having trouble having a child,

and they take a bunch of
eggs out of the mother.

So let's say they take
maybe 10 to 30

eggs out of the mother.

They actually perform a surgery,
take them out of the

ovaries of the mother, and then
they fertilize them with

semen, either it might come
from the father or a sperm

donor, so then all of these
becomes zygotes once they're

fertilized with semen.

So these all become zygotes,
and then they allow them to

develop, and they usually allow
them to develop to the

blastocyst stage.

So eventually all of these
turn into blastocysts.

They have a blastocoel in
the center, which is

this area of fluid.

They have, of course, the
embryo, the inner cell mass in

them, and what they do is they
look at the ones that they

deem are healthier or maybe
the ones that are at least

just not unhealthy, and they'll
take a couple of these

and they'll implant these into
the mother, so all of this is

occurring in a Petri dish.

So maybe these four look good,
so they're going to take these

four, and they're going to
implant these into a mother,

and if all goes well, maybe one
of these will turn into--

will give the couple a child.

So this one will develop and
maybe the other ones won't.

But if you've seen John & Kate
Plus 8, you know that many

times they implant a lot of
them in there, just to

increase the probability that
you get at least one child.

But every now and then, they
implant seven or eight, and

then you end up with
eight kids.

And that's why in-vitro
fertilization often results in

kind of these multiple
births, or reality

television shows on cable.

But what do they do with all
of these other perfectly--

well, I won't say perfectly
viable, but these are embryos.

They may or may not be perfectly
viable, but you have

these embryos that have the
potential, just like this one

right here.

These all have the potential
to turn into a human being.

But most fertility clinics,
roughly half of them, they

either throw these away,
they destroy them, they

allow them to die.

A lot of these are frozen, but
just the process of freezing

them kills them and then bonding
them kills them again,

so most of these, the process of
in-vitro fertilization, for

every one child that has the
potential to develop into a

full-fledged human being, you're
actually destroying

tens of very viable embryos.

So at least my take on it is
if you're against-- and I

generally don't want to take a
side on this, but if you are

against research that involves
embryonic stem cells because

of the destruction of embryos,
on that same, I guess,

philosophical ground, you
should also be against

in-vitro fertilization because
both of these involve the

destruction of zygotes.

I think-- well, I won't talk
more about this, because I

really don't want to take sides,
but I want to show that

there is kind of an equivalence
here that's

completely lost in this debate
on whether embryonic stem

cells should be used because
they have a destruction of

embryos, because you're
destroying just as many

embryos in this-- well, I won't
say just as many, but

you are destroying embryos.

There's hundreds of thousands of
embryos that get destroyed

and get frozen and obviously
destroyed in that process as

well through this in-vitro
fertilization process.

So anyway, now hopefully you
have the tools to kind of

engage in the debate around stem
cells, and you see that

it all comes from what we
learned about meiosis.

They produce these gametes.

The male gamete fertilizes
a female gamete.

The zygote happens or gets
created and starts splitting

up the morula, and then it
keeps splitting and it

differentiates into the
blastocyst, and then this is

where the stem cells are.

So you already know enough
science to engage in kind of a

very heated debate.