So in this picture, we've got a pregnant mom and a little fetus
inside of her uterus.
That's the name of this little chamber
that the fetus is hanging out in.
And this uterus is an organ.
And women have this organ.
And it's a very, very strong organ, a very muscular organ.
In fact, if you've ever gone to a delivery
and you've heard people chant, push, push, push,
they're literally encouraging mom to push down on this uterus
and help the baby come out into the world.
So this uterus is the room in which the baby lives.
But the environment in which the baby lives
is actually very different, as well,
from how we live outside in the sense
that there's amniotic fluid in this space.
Amniotic fluid, and the baby is actually
swimming in this fluid for months at a time.
So for nine months, baby is swimming in amniotic fluid.
And that brings up some obvious questions--
how is baby able to breathe or eat?
How does it take care of its needs?
So let's think about what those needs are.
Let's enumerate them.
One of them is oxygen.
So how does the baby take in oxygen
if it's not getting it from the lungs?
And the lungs are actually full of amniotic fluid, by the way.
How is it able to get nutrients?
Things like sugar or glucose that it needs for energy.
So I'll put an example, glucose.
How about let's think about waste.
How does it get rid of things like carbon dioxide?
For us, it's very easy.
We just exhale or take a breath out.
But how does a baby do that?
If I just said that the lungs are full of fluid,
how does it get rid of waste products like carbon dioxide?
And it turns out all of these kinds of issues are obviously
very important, and the mom and the baby
kind of work together a solution.
This is the first chance for mom and baby
to really work together on something.
And the solution is something called the placenta.
And you may have heard of the placenta.
And the baby actually sends a couple
of vessels up to the placenta, and these
are little umbilical arteries.
It also sends up an umbilical vein to the placenta,
and the vein brings blood back from the placenta.
And all of these vessels, all three of these,
make what we call the umbilical cord.
So you may have heard of the umbilical cord.
And now you know what's inside of it.
The umbilical cord, actually, if you were to cut it,
I'm just going to show you what it
would look like if you were to cut across it.
It's actually an easy thing to remember,
because it has a big floppy little vessel right here,
and that's the umbilical vein.
And it's got oxygen.
And that's why I'm drawing it as red, even though it's a vein.
Because it's coming back to the heart,
so that's why we call it a vein.
And you've got umbilical arteries.
And these two actually don't have too much oxygen.
That's what I'm drawing them in blue,
just to show that they are low in oxygen.
But they're called umbilical arteries
because they're going away from the heart.
So the umbilical arteries and the umbilical vein
look like this.
And actually, they're not just freely floating out there.
They're actually encased in this jelly.
And the jelly is called Wharton's jelly.
I'm actually just going to redraw this,
just to show you how I remember this,
because sometimes it's hard to remember
if there's one artery or two arteries.
And I think of the mouth as a vein, or a V,
and I think of the eyes as two little As.
So that's my little trick for remembering
that there are two umbilical arteries and one
umbilical vein, and that they're all
encased in the Wharton's jelly.
And this is the umbilical cord.
So this is the overall picture, but now I want to go into some
detail to really get us to understand how the placenta
works, because it honestly is one of the most interesting
organs in the sense that it allows us to do things that we
simply cannot do today, but we could do for many,
many months at a time.
So I'm going to invert the way that I drew this.
I drew this one way above, and I think
you'll see how I flipped it around here.
This will be the uterine wall.
And again, remember the uterine wall
is a nice, strong, muscular wall.
And let me label it so it's clear-- I'll just
call it uterus.
The wall of the uterus, anyway.
And on the insides, you've got-- let's see,
working from the outside in.
Let me draw some of mom's blood vessels.
So she's got some blood vessels coming off like this,
and this is a little uterine artery.
And this, of course, gives oxygen to the uterus.
We said it's a big muscle, so it definitely needs blood vessels,
like arteries and veins.
And I'll draw a couple of them.
Let's draw another uterine artery over here,
and I'll draw one third one over here.
And of course, there are many more than three,
but I just want to give you the concept that there
are some uterine arteries.
And there are also some uterine veins.
Let me draw some uterine veins as well,
and I'll draw one over here.
So these blue ones are the uterine veins,
I'll label this one over here.
So what they're doing is they're actually
going through a layer of tissue.
So let me draw in a layer of tissue for you
so you see exactly what I mean.
There's a layer of tissue here, and they're going through it.
And this layer of tissue is mom's tissue.
So actually, I'm going to label it mom's tissue,
or I'll just call it mom's.
And it looks a little bit-- and you'll
have to stretch your imagination--
but looks a little bit like a plate.
So this entire thing that I'm shading in in red
is one of the parts of the placenta.
So we've already started drawing the placenta.
And this part is known as the basal plate.
So if you're talking about the basal plate,
you're talking about this bit of tissue
here with the blood vessels, the uterine arteries,
and the uterine veins.
And just to be clear, it belongs to mom.
So this is mom's cells.
And now we get into some really fun stuff.
So all these uterine arteries, they squirt out blood.
And they don't go into any other vessel,
they actually just kind of squirt out blood
into an open area.
So let's say there's a red blood cell here,
this red blood cell literally could physically
touch a red blood cell over here.
They literally just could come up
and meet and maybe shake hands.
And then they could then go down the veins.
So this is really, really different
from how we usually think about blood cells traveling always
within a vessel.
Because here, it's kind of a pool.
And you have this kind of circulation
that happens because you have these red blood cells, as I've
drawn them, kind of going up into the middle
and then circulating into the veins.
So you have this interesting circulation where you basically
have blood coming up through the arteries
and down into the veins.
And the way I think about this-- and you can maybe
choose your own analogy, but for me I
think of it a little bit like a hot tub.
And the uterine arteries are like the jets of water coming
up, and the blue veins, the uterine veins,
are literally like the drains in the hot tub.
So it becomes almost like a swirling pool
of red blood cells.
Now importantly, these red blood cells have with them oxygen.
They have nutrients.
They have a lot of the stuff that our fetus
is interested in getting access to.
So let's switch gears.
Let's think about our fetus.
Our fetus has got, we said, a couple of umbilical arteries
coming down.
And I also said that they're coming down inside
of this Wharton's jelly, this umbilical cord of Wharton's
jelly.
And actually, what happens is that the vessels actually
branch out, and they split up.
So the uterine arteries, they form lots and lots and lots
of little branches, and I'm going to draw them in for you.
And let's say that the branches go all over the place.
Let's say they go like this.
Let's draw five or six branches over here,
and let's draw some branches down on the side, too.
You've got lots of branches off the uterine arteries,
and they want access to the oxygen and nutrients.
So guess what they do?
They just push in.
In fact, you have little cells here.
I'm going to draw some pushing in right here.
You've got little cells that I'm drawing in white called
trophoblasts.
And they literally do this.
They just kind of push in.
So these white cells are trophoblast cells.
And they're good at invading.
You can think of them as invading.
Or if you want to be less aggressive,
you can think of them as being just curious.
So these little fetus cells called
trophoblasts start pushing in, and within the trophoblast
is a little blood vessel.
And this blood vessel now is in very close contact
with mom's red blood cells.
You've got red blood cells coming up alongside of it.
And now, what's going to happen through diffusion
is that oxygen is going to go into the fetus's blood cells.
So oxygen is going this way, as well as nutrients.
So oxygen and nutrients go inside
and then you have carbon dioxide leaving.
So carbon dioxide actually goes into the pool of blood.
So it's a really, really cool thing
that the red blood cells aren't touching-- the mom's red blood
cells are not touching baby's red blood cells,
because of course, baby's red blood cells
are within blood vessels.
These are within blood vessels.
These things right here are not open-- they're closed vessels.
And once that exchange happens, they continue to stay closed,
and you get a little capillary coming back.
And of course, you've got capillaries coming back
from every part of this.
So all of these have been doing the same thing,
going inside of this pool of blood.
And it actually gets a little more complicated
than the way I've drawn it.
In fact, a more accurate drawing might be with more branching.
You might have something like this, where it really
has lots of surface area, and it comes back around,
and you have the blue vessels kind
of going into each one of these little finger-like projections.
And you have a lot of gas exchange happening.
So this would be a better way of drawing it,
but the concept is the same.
You basically have all of this wonderful diffusion happening,
and as a result you actually have
nice, rich, oxygenated blood returning to the baby.
So this is finally allowing the baby
to have access to oxygen and nutrients
and get rid of its waste, its carbon dioxide.
And so each one of these is actually doing the same thing
with red or oxygenated blood coming back.
And instead of having two vessels,
it all dumps into one vessel down the middle.
And this vessel, as we already know,
is called the umbilical vein.
So this is actually the umbilical vein.
Now if we called the bottom one the basal plate, then
of course, you're guessing that there
must be some name for this.
And this, of course, has its name,
called the chorionic plate.
Chorionic plate.
And this one, you can already tell,
this has all the cells from the fetus.
So this belongs to the fetus.
So you've got some tissue that belongs to the fetus, that
would be the chorionic plate and all of its contents.
You've got some tissue that belongs
to mom, that's the basal plate.
And then you've got some shared tissue or space in here.
Because all these little projections belong to the baby,
but the actual pool, this pool of blood that's circulating,
that pool of blood belongs to mom.
So really, the placenta is a combination
of all of these things.
So I think of the placenta, then, as the first time
that mom and baby work together for a common purpose.