Fetal structures in an adult | Circulatory system physiology | NCLEX-RN | Khan Academy

So I left up this picture.

This is a picture of how
blood flows in a baby right

after it's born, and
all the different parts

of that circulation and
all the different names.

And the reason I left
this up is because I

want to talk about
all the changes

that then happen
as we grow older.

So you know, let's take
myself for example.

I'm an adult now.

And as an adult, what are
all of the structures called?

Or what becomes of all
these things in my body?

Well, for starters, if I
look down at my belly button,

I'm not going to see
a little smiley face.

Right?

I'm not going to see
any blood vessels.

I'm just going to see skin.

And that's because all these
blood vessels have really,

for a long time in my body,
not been delivering blood.

So that's the first kind of
change I want to point out.

Now, what used to be the
umbilical vein over here

has, in my body,
become a ligament.

All of that, from
many years ago,

there was some clotted
blood in there.

But over the years-- in
fact, shortly after birth,

this started getting fibrosed.

And lots of tissue kind
of fell into this area,

and it became almost like
what happens with a scab.

You get lots of
proteins in there.

And you don't really have
a space anymore for blood

to flow.

So this becomes a ligament.

In fact, there's a
ligament that extends

towards the portal vein.

And even the ductus
venosus, that

becomes a ligament as well.

So all these become ligaments.

In fact, they have
fancy Latin names.

So let me actually just
replace this umbilical vein

with what it's
called in my body.

And in my body we call it
the ligamentum teres hepatis.

So if you want to impress
your friends, you can say, ah,

do you mean my
ligamentum teres hepatis?

And that's what becomes
of the umbilical vein.

This is actually kind of
a tricky word to remember.

But "hepatis" refers to liver.

So you know that this is
headed towards the liver.

So you can remember it that way.

And over on this side,
this ductus venosus, well,

it's no longer a
duct, right? "Duct"

implies that you can actually
pass something through it.

And the way I've drawn it,
it's a ligament, right?

So it's a ligament.

And we're actually going to
name it something fancy as well.

We'll call it
ligamentum-- so kind

of starting out the same
way as the other one.

This one is ligamentum venosum.

So remember it used
to be ductus venosus.

So now we call this
the ligamentum venosum.

So that's fairly
easy to remember.

So two ligamentums
so far, right?

And I promise you we're going
to have a few more before we're

done.

Now moving on, we have blood
entering the right atrium.

And you know blood
in the fetus used

to go from the right
atrium to the left atrium

through the foramen ovale.

But then we talked
about how it closes

when the pressure
on the left side

gets higher than the
pressure on the right side.

And so when it closes, the
idea is that, over time, there

is actually going to be
some-- some tissue is going

to basically form
between those two flaps.

And so it actually
creates a real seal.

And when that happens, then
that space-- this space right

here-- becomes known
as the fossa ovalis.

So that's what it might be
called in me or you today.

If you were to actually look
inside of the right atrium,

you would spot a
tiny little hole

on the wall that has
tissue on the other side,

and that's called
the fossa ovalis.

But it turns out
that in many adults,

you actually don't
have a real seal there.

So the way I've drawn it
where there's actually

a little seal between the
two, that may not even happen.

In fact, let's say in
about 20%, or sometimes

you'll see the
number 25% of adults,

you actually just
have two flaps that

could theoretically kind of move
apart from each other again.

And so if you're one of those
20%, let's say 20 to 25%,

if you're one of
them, then you'd

have what's called a
patent foramen ovale.

And if you're part
of the majority,

then, the other 75 to 80%,
then you'd have a fossa ovalis.

So really all that means
is that some people have

a real seal that connects
the two flaps of tissue,

and some people
don't have a seal.

And so the two
flaps can actually

move apart from each other if
the pressure on the right side

gets really high.

So in a person with a patent
foramen ovale, theoretically,

if you had a lot of pressure on
this right side, on that spot,

you would actually
open that flap up.

And you could actually
have a situation

like this, where all of a
sudden now, you can actually

move blood between the two.

So this is actually an
interesting thought process.

You can actually move
blood from the right side

to the left in people
with what they call a PFO.

But for most people, the
pressure on the right side

really never gets that high.

So even if you have a
PFO, because the pressure

on the right side
is almost always

lower than the left
side, it almost always

means that this
flap will stay shut.

So even with a PFO, the
vast majority of people

never even know it.

In fact, they go on living
their lives very happily,

even though there's really no
seal sealing that thing off.

Now moving onwards, we
have the ductus arteriosus.

And so we know that this,
shortly after birth,

is going to kind of tighten up.

The muscles constrict when
they face all those high oxygen

levels and they can sense
the low prostaglandins.

And this ductus
arteriosus then, it really

doesn't have this name anymore.

It gets changed.

And in an adult, I'm
going to give you

a moment to guess
as I write it out.

Again, ligamentum-- and
I'll give you a clue.

Try to remember what we
called this guy over here.

We're going to call this
one ligamentum arteriosum.

So you're getting the hint
for how we name these things.

And now if we follow the
blood down, down, down,

down the aorta, it goes into
the internal iliac artery.

That's this guy on the left
and this guy on the right.

And the internal iliac
artery has lots of branches.

And we haven't drawn all the
branches, but there are many.

And eventually, it
was going to lead

into what we used to call
the umbilical artery.

Now, these umbilical
arteries, just

like the ductus
arteriosus, actually

starts kind of constricting
once the oxygen levels go up

and once the prostaglandins
levels go down.

And when it constricts,
it turns into a ligament.

And this is also
because there's no blood

flow through this area.

And the last place where
there is blood flow

is going to maintain blood flow.

So there were branches, I said.

And of course, through
these branches,

blood is flowing to
other areas, right?

Blood it's going to, let's say,
different structures inside

of our pelvis.

And these last couple
of branches right here,

these are headed
towards our bladder.

So sometimes you'll see that.

You'll see that
they'll say part of it

turns into an artery
towards the bladder.

And the other part
turns into a ligament.

So let's actually erase this
word, "umbilical artery,"

and replace it with
the correct word, which

is that it turns
into the medial--

and actually, this is very
important, because people get

confused on this
point all the time.

I'm going to point to the L--
medial umbilical ligament.

And there are two of
them, of course, right?

Because there are two arteries.

So I should write medial
umbilical ligaments,

two of them.

So then just to
kind of summarize,

we have a few ligaments down
here by our belly button.

We have one important
ligament that's in our liver.

We also have one up by
our aorta separating it

from the pulmonary artery.

And finally, we have-- either
you have a sealed-off version,

and we call that a fossa
ovalis in our heart,

or you have a patent
foramen ovale.

And even if that's the
case, for most of us,

that is not a problem.