Umbilical vessels and the ductus venosus | Circulatory system physiology | NCLEX-RN | Khan Academy


So here we are. We’re looking at the placenta. I’m just going to outline the
parts that are specifically considered the placenta. That’s this bit right here. And I’m going to
orient you by labeling the pink wall
that’s around this. You remember that’s
called the uterus wall. That’s this wall right here. This is our uterus, and this
is a very muscular organ. Remember, this is going to
help us squeeze the baby out. Or it’s going to help mom
squeeze the baby out, anyway, when it’s time for delivery. Now, in the placenta,
there are different parts. And there’s an inside part. Remember, mom is on this
side, and baby is on– or fetus is on this side. And when I say baby and
fetus, I kind of mean them interchangeably. I recognize that they’re
not exactly the same thing, but when I mean baby, for
the purposes of this video, I mean the unborn
baby, the baby that’s still getting
nutrition from mom. So this layer then,
this little layer that I just put in here, this
is the basal plate, remember. So this is mom’s tissue. And on the other side, we
have the chorionic plate. Remember, that’s
the fetus tissue. The chorionic plate is full
of lots of blood vessels. And in between the two–
this is the interesting part, where all the
magic is happening. In between the two,
remember, there’s blood. There’s a giant pool
of blood, and it’s full of oxygen and
nutrients, and it takes away waste, like carbon dioxide. All the things
that the baby needs are located in
this pool of blood. And you remember,
the pool of blood, the way we even got
this pool of blood is that we have
little arteries here, uterine arteries that are
pushing blood into that pool. And then it’s getting recycled
by all these uterine veins. So you’ve got this circulation
happening on the mom’s side. And within the pool of blood,
remember, the fetus is actually sticking its little
capillaries in there. So the fetus is
sticking its capillaries into the pool of blood. So that middle area,
this middle zone, is really where the
diffusion is happening. Remember, the diffusion
is happening from the pool into the fetus’s capillaries,
capillaries right here. So fetus capillaries are pushing
their way into that pool. And that’s where they’re
getting their oxygen nutrients and dumping off
the carbon dioxide. So the question is, how
does it go from there back to the fetus? So the fetus, of course, has
umbilical arteries and veins. And this red one is
the umbilical vein. And how does the oxygen
get from where it is now all the way back to
the different organs? And I’m going to draw
this little yellow circle. You can imagine this is,
let’s say, the belly button. And it’s interesting
because so much used to happen in the
belly button for the fetus, and by comparison,
not much happens in adult humans with
the belly button at all. So you’ve got, let’s say, one
artery there, one artery there. And I’m trying to draw
a little face here for us to remember
what this looks like. So this is our little
face with two eyes. So the umbilical vein is in red
and that’s– just to label it– this guy. And then you’ve got the
two umbilical arteries, and those are in purple. And those are the two eyes
of our umbilical cord, umbilical arteries. So what I want to do
now is to figure out exactly how does
blood, as I said, go from the umbilical vein
all the way back to the rest of the body. And to do that,
what we need to do is actually sketch out
what’s going on in the body. So I’m going to
draw the diaphragm. Remember, the diaphragm is
a muscular– a big muscle, rather. And It’s very
muscular, of course, lot of skeletal muscle in here. And above the
diaphragm and below the diaphragm are
a couple of organs that we’re going to
have to talk about. And the first one,
above the diaphragm, is a four-chambered
organ– I’m sure you’re very familiar with this
guy– called the heart. So the heart is sitting up here,
and it’s got four chambers. And I’m going to quickly
label the four chambers. You’ve got the right atrium,
and the right ventricle down here, the left atrium, and
the left ventricle down here. And so this is my heart. And the other
organ– and actually, let me label this muscle just
in case we lose track later. This is our
diaphragm, of course. And the other
organ– not muscle. The other organ is the liver. This liver is this huge organ,
actually sits right below the diaphragm. So it’s actually quite close
to the heart, as it turns out. And the liver does a
number of important things. But right now we’re
just going to talk about the anatomy of what’s
going through the liver. So you’ve got a vein here. I’m going to label it here. It’s called the portal vein. And don’t worry so much
about the names of things, but I just want to diagram
out how blood is traveling. And you’ve got another vein here
I’ll draw a little bit longer, just to give me
more space to write. And this is the
inferior vena cava. You remember this vessel. This is the big vein that
brings in a lot of blood from different
parts of the body. And you have the aorta. And remember, the
aorta is actually going to go off
the left ventricle, and it’s going to
go behind the heart. So I’m going to just
draw dashed lines. And let’s say it
comes through here. And I’m showing it– go
down, down, down, down, down, and split up. It’s going to split
up at the legs. So this is where the legs are. And actually these
internal branches, let’s say this branch right
here and this branch right here, these branches are called
the internal iliac branches, or internal iliac arteries. You call them internal
iliac arteries. And I’ll explain
in just a moment why I bothered to name
these guys as opposed to all the other arteries and
branches I could have named, because, of course, there
are many, many branches off the aorta. But these are going to
be very important for how the fetus’s blood gets around. So let’s follow blood now. Let’s start back at
the umbilical vein and see what happens. So the umbilical vein blood
I’ll just show going this way, and this umbilical
vein blood is now on the inside of the
body of the baby. So if I said this is the
belly button, then, of course, that must mean that everything
on this side of the belly button is the body of the baby. So we’ve got the
baby, there, and it’s going inside the baby’s
body, and the vein travels, travels, travels. And it has a choice. It can either go over
to the portal vein, or it can go over to
the inferior vena cava. And we’ll follow
one path at a time. Let’s do the inferior
vena cava path first. When the oxygenated red
blood comes and mixes with the deoxygenated
blue blood, it actually forms kind
of purplish blood. That’s why I’m
drawing it this way. Remember, purplish
represents somewhere in between having a lot of oxygen
and having a very low amount of oxygen, somewhere in between. So that’s why I drew that red
and blue turning into purple. So if I have
purplish blood there, that is one of my
two paths I said. In fact, this part of
the journey, this part, is only possible because
there’s a tube there. And that tube is actually
called the ductus venosus. And essentially what
this is is a shortcut. Now, if that’s the shortcut,
what’s the other path? Makes you wonder, right? Well, the other path is actually
much, much longer, obviously. And I’m going to
show it over here. So if it joins the portal
vein, instead of going down the ductus venosus, if
blood goes this way, then it’s going to branch
out into different parts of the liver. It’s going to go to all the
different parts of the liver. And then it’s going to
go into capillary beds. So it’s going to go and
get very, very, very tiny. So let’s follow one
branch, let’s say this guy. It’s going to get into very,
very, very tiny capillary beds. And then on the other
side, it’s going to get picked up by
tiny capillary beds, and it’s going to
get brought back. And it’s going to
join up with blood from all the different
parts of the liver. And it’s going to eventually
be part of a vein. And this vein right here
is called the hepatic vein. So either way, even
if it takes a shortcut or doesn’t take the
shortcut, eventually blood is going to make its way back
into the inferior vena cava and into the right atrium. So overall, the
goal is the same. It’s going to get
to the right atrium. But one way, taking
the ductus venosus, is much quicker
than the other way. And that’s important, because
you want– from the fetus’s perspective, you want this
wonderful umbilical vein blood, which is rich and
full of oxygen, to make its way
back to the heart quickly so that it can get
pumped out through the aorta to the rest of the body. Now there is a very
interesting way that blood makes its way
through the heart itself. And we’re going to skip over
that for the time being. I’ll get into that
in another video. But it gets into the aorta. That’s the next part. And it goes down the aorta. Blood gets pumped to all
different parts of the body. And I’m drawing it
as purple, still, because, of course, it’s
not very, very oxygenated like the umbilical vein
is, but it’s also not completely deoxygenated like
in the inferior vena cava. It’s somewhere in between. And blood goes down into
the internal iliac arteries. And from there,
you actually have branches that go to
one umbilical artery on this side and one umbilical
artery on the other side. So you actually
have branches that go off of the
internal iliac artery and go to the
umbilical arteries. And, of course, from that
point, you know what happens. Then both arteries go
into the pool of blood that mom has set up for
the fetus and exchange at the capillaries for
oxygen and nutrients. And the new blood, then, is
very, very highly oxygenated. And the journey repeats itself. So just to make
sure we’re clear, let me just start
from the beginning and go through it
again, Now I’m going to use a little blue
dot to track– oh, let’s say a little green
dot– to track where we are. So blood starts in the
umbilical vein right here. And let’s say that’s our
first starting point. It goes to a little branch
point, where it either can go down into the
ductus venosus– that would be this one. Or it can go this way,
and join the portal vein. It has an option. If it goes the long way, then
it goes into the portal vein, and it goes off
into some capillary, gets picked up and
dragged back, and joins the hepatic vein, which
eventually also merges with the inferior vena cava. Of course, if it
takes the shortcut, that route is much quicker. So that’s the whole point
of the ductus venosus, is to skip over the liver. Eventually the blood makes
its way to the right atrium. And again, it’s going to
have an interesting path through the heart, which we’ll
get into in a future video. But for right now,
let’s just assume it gets through the heart
and gets out into the aorta. Now blood is going
to go down the aorta, is going to branch off
into one of the two legs, because these
branches go to the two different legs of our fetus. And it’ll go down into
the internal iliac artery right here and on the
other side right here. And at that point,
it’ll shoot up– some of it, anyway, will shoot
up into this umbilical artery, into these umbilical
arteries, these two. So now blood is over here into
our two umbilical arteries. And it’s going to
go down, and it’s going to exchange inside of that
pool of blood in the placenta, and it’s going to
turn around and join our umbilical vein again. So that’s the loop
that we follow, and that is the fetal
circulatory system.

37 Replies to “Umbilical vessels and the ductus venosus | Circulatory system physiology | NCLEX-RN | Khan Academy”

  1. wonderful presentation! i wanted to add one key point that i feel u may have missed. fetal shunts are present also because the mother is doing the metabolism for the child, trough the placenta, hence the lungs and liver functions are not needed.

    i watched 2 of ur videos about this topic and didnt hear it mentioned, but i see there are a couple more so i dont know if u mention them there. keep up the great work!

  2. This video kicks butt. 12:32 of this w graphics or sitting through a 2 hr lecture with a 55 year old uninterested and tenured diabetic & making no learning progress.

  3. This was a truly helpful lesson. I'm not sure if you're aware of this, but it is next to impossible to find a clear, accurate illustration/animation alongside an instruction as to how the Ductus Venousus works. All I EVER heard was "it makes blood skip the liver". Now I know How, Where, and Why it does that. Thank you!

  4. Great video, thank you soo much, but I do have a question for you. Does mom and fetus blood ever get mixed up in this whole process at all?

  5. If you don't mind i'll try to give a beginning of answer.
    Answer: No, the blood of the mother and fetus must NEVER mix, there would be a rejection because of the major complex of Histocompatibility. If the bloods "touch" then the consequences will most probably be the death of the fetus. This is why the placenta exists, to ease the exchanges of nutrients, Immunoglobulins and other., hope this helps.

  6. This is not entirely true (at least to my knowledge). Small (and I mean really small) quantities of blood will mix. Consider the rhesus incompatibilities between mother and child that can sometimes occur. In a first pregnancy where mother and child are opposing rhesus (+ and -) small amounts of blood can mix and mother can produce antibodies against antigen D (rhesus +). In a second birth antibody against rhesus can cross placenta (being IgG mediated) and cause haemolytic anaemia in the fetus.

  7. I love all these videos, but I tried it with the closed captions today, and it was pretty funny. A lot of #%$ like it's trying to sensor the inferior vena cava

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