Baby circulation right after birth | Circulatory system physiology | NCLEX-RN | Khan Academy


We’ve talked about
fetal circulation, and I’ve talked about all
the different interesting adaptations that the
fetus has to make sure it can adjust to life
within the uterus, within mom. But when the baby
comes out– let’s say the baby is just
delivered– there’s got be a lot of
changes that happen. In fact, these
adaptations, each of them plays a role in the first few
minutes, hours, days of life. And so what I wanted to do is
go through all the adaptations, think through them,
and see what’s happening actually after birth. So we know what
happens before birth and how the baby
adjusts there, but how does this now
translate into what’s going to happen
after birth and what the baby has to do now
that it’s separated from mom and
breathing on its own? And the first two things
I want to point out are the idea of– what are the
big things that are changing? And one big thing is, of
course, that the placenta, which the baby’s been using for 40
weeks, or nine months or so, is no longer around. The placenta is removed
from the baby’s circulation. We’re going to cut it away. And the second big thing
that’s going to happen is that the lungs
get used to bring in air for the first time. So the lungs take in air. So these are the two huge
things that are going to change. And these two things
are going to end up affecting a whole lot of
other things, as well. So let’s get started. Let’s see what happens when
the placenta gets removed and when the lungs take in air. Let’s start with the placenta. So let’s say that you decide
that the baby is now delivered, and you want to cut the
cord, cut the umbilical cord, and put an umbilical
clamp right there. And this is often done. You’ll see this done in
movies, or if you’ve ever gone to a delivery, you’ll see
this done pretty routinely. So this is a little
umbilical clamp, and it’s clamping the cord. And if you’re ever worried about
whether that hurts the baby or the mother, it doesn’t. Because the umbilical
cord does not have nerves. So that’s kind of the first
interesting thing about it. But this stuff, remember–
this pale yellowish stuff that’s kind of jelly-like–
we call this Wharton’s jelly. Wharton’s jelly. And one of the
things that I always thought was really cool
about Wharton’s jelly is that it’s a really
interesting Mother Nature-type idea, that the Wharton’s
jelly starts contracting. It gets kind of tighter around
the three vessels– the two eyes and the smiley face
that I’ve drawn here, which are the two umbilical
arteries in the vein. The Wharton’s jelly starts
squeezing around those vessels as soon as the
temperature falls. So temperature
falls– and remember, the temperature in
the mom is going to be much warmer than it is
outside in the delivery room, so immediately that Wharton’s
jelly is exposed to cold air. And when the temperature
falls, the Wharton’s jelly starts to contract,
causes contraction. And of course, that’s going to
squeeze down on all the vessels inside. It’s going to basically
clamp down on them. And so it’s almost like we have
this man-made clamp that I drew in orange, but the
Wharton’s jelly is kind of a natural clamp
that we already have. So we’re taking this very
low-resistance placenta– remember, it used to be very
low-resistance, a lot of blood liked to flow in
that direction– and creating really
high-resistance. So this is the
first big change, is that the placenta
gets removed and you go from low-resistance
to high-resistance. So that’s a key idea. Now as a result of the
high-resistance– remember, there used to be blood flowing
through the umbilical vein, but now in the first
few days, there’s really no blood
flowing through here. All the blood
starts clotting off. And that’s true even
of the ductus venosus. You get some blood
clots in there. So you don’t really
have any flow anymore, and in the first few days,
you really completely lose any flow
through those things. So this becomes
non-used, or unused, over the first few days of life. Now you still have blood
flowing from the portal vein into the liver, and you
still have blood going up the inferior vena cava, and
this is all deoxygenated blood, so that is still
the same as before. And this deoxygenated blood
now has no new fresh oxygen to mix with. So I’m not going
to color it purple. I’m going to leave it
the same blue color. So deoxygenated blood
comes up from the legs and it comes down from
the head and the arms, from the superior vena cava. And now all this
deoxygenated blood fills in the right atrium,
and some of that blood is going to now go into the
right ventricle, so let’s color that in blue. And it’s going to
get squeezed out into the pulmonary arteries
from the right ventricle, so let me color that in the
same deoxygenated blue color. And this is headed
toward the lungs. Now in the lungs,
what was happening? Well, initially, remember
we had these little alveoli. And they’re full of fluid. And that fluid now is going
to get replaced by air. So air is going to
push the fluid out. Air is going to push
all that fluid out. And what’s on the outside? Well, we’ve got
little capillaries. So we’ve got these
capillaries, and the fluid will enter the capillary. But remember, right before the
capillary is the arteriole. Let me actually sketch
it a little bit smaller, the arteriole. Because it used to
be very constricted. Remember, there was that hypoxic
pulmonary vasoconstriction. But now that you
have air in there, the oxygen levels are
rising in the alveolus. And what that’s
going to do is that’s going to send a signal over
to the arteriole– this is our arteriole– to say,
hey, it’s time to open up now. It’s time to finally dilate. So this arteriole is excited. It’s never really been very
dilated before in its life. So it finally says,
yay, it’s my chance. So it dilates. It dilates like this. And it’s nice and plump and big. And when it gets big, what
does that really mean? It means that the
resistance has fallen. Resistance has fallen. So remember, the lungs used
to have high resistance. And now, millions of alveoli
are causing the arterioles to open up and resistance falls. And this happens, of
course, on both sides. So on the left lung
and the right lung, the resistance is falling. And that deoxygenated
blood now can flow in. Because initially, it
wasn’t really wanting to flow in because the
pressures had to be so great. But now the pulmonary artery
pressures are falling. It’s easier to actually get
the blood into the lungs. And that means, of course,
the right ventricular pressures are falling. And the right atrial
pressures are falling. So the entire right
side of the heart now is working under
lower pressures because the resistance in
the lungs has gone down. And now the resistance
in the lungs going down, that means that more
blood is going to go in, and if it goes in,
it’s going to go into all the little
thousands of capillaries and it’s going to
get oxygenated. And those capillaries are going
to send all that blood back and it’s going to flow
into the left atrium. So you have all this fantastic
oxygenated blood coming in from both sides, coming
into those pulmonary veins. So now tons of
oxygenated blood is dumping into the left atrium,
which is different than before, because you didn’t have
much flow through the lung. So now you’ve got lots of
blood kind of flowing in here. And at the same time, the
pressures on the right side have fallen. So if pressures on the
right side have fallen, think about what’s happening
to our foramen ovale. Before, blood was actually
kind of gushing through there. But now, because the pressures
on the right side are so low, this little flap of tissue,
like a little valve, closes off. And so now you can actually
see that this flap of tissue will do this. It’ll close off. Because you basically
have more pressure on the left side
than the right side, and it pushes that
flap of tissue over. And now the foramen ovale
is basically closed. And this happens, actually,
in the first few minutes– first few minutes after
a baby is out of the mom, you actually see this foramen
ovale close, which is amazing. Now blood continues
to go down, it likes to go into
the left ventricle. So it’s going to go
down here and get squeezed into the aorta. So let me show– now oxygenated
blood for the first time kind of getting into
the aorta this way. And then you have the question
of the ductus arteriosus. Remember, initially
the reason that blood was moving from the pulmonary
artery into the aorta was because the pressures in the
pulmonary artery were so high. But now the pressures
are pretty low, the pressures are much lower. If anything, you would actually
have flow going this way because the aortic
pressures are higher than what the pulmonary
pressures are now. But it turns out, interestingly,
that in the first few hours of life, you actually
have some constriction of the muscles in that
ductus arteriosus. So that ductus arteriosus has
smooth muscle in the walls. And those smooth
muscles are going to sense that now
oxygen levels are high. They’re going to
sense the increase in oxygen levels in the blood. And they’re going to
start getting twitchy, they’re going to want
to start constricting. The other thing that the
ductus arteriosus senses is that the placenta is removed. How would you sense
something like that? And how would the ductus– which
is over here– how would it sense that the placenta– which
is over here– how would it know that it’s been removed? Well, it turns out
the placenta actually makes a little chemical
called prostaglandin. And when prostaglandin
levels fall, when prostaglandin
levels go down, then the ductus arteriosus
also is more willing or able to close down. So those little muscles inside
of the ductus arteriosus– remember, it’s like a
little artery, in a sense. It’s got smooth
muscle around it. Those muscles are
going to constrict, they’re going to tighten down
when the oxygen levels go up and when the prostaglandin
levels go down. It’s going to sense that. And so it’s going
to know that hey, it’s time for me to close
up shop and tighten down. And over time– and I’ll
say over a course of hours– this is going to happen. So let me actually just jot
down the time frame for you. So over the course
of a few hours, the beginning of
constriction will happen. So over time, this
will actually get kind of tighter and
tighter and tighter. Let me sketch it
out, getting smaller and smaller and smaller. You actually have on
the inside of it maybe a tiny little opening, and then
over time, a smaller opening, and over time, no
opening at all. So that’s going to
happen at the beginning of the first few hours of life. Now, following the
blood all the way down, you actually have aortic blood
with oxygen flowing down here into the, let’s say, the right
leg and into the left leg, over here. And there are these
branches, these big branches, called the internal iliac
branches, and off of them, where the umbilical
arteries, right? The umbilical arteries
where branches off of the internal iliac. And what’s going to
happen is that you’re going to still get blood
flowing to other branches off the internal iliac, like
this little branch might go to the bladder. But that last little
bit, really, there will be no flow through
there because the resistance is so darn high. Because the resistance
over here is so darn high, no blood is going to want
to go in that direction. In addition, the
umbilical arteries, just like the ductus arteriosus,
have smooth muscle in them. And so that smooth
muscle is going to respond to the very
high levels of oxygen that, for the first time,
these arteries are seeing, and low prostaglandins that
are kind of circulating. And they’re also going to
kind of start constricting. So just as the ductus
arteriosus started constricting, these arteries also
start constricting. They get tighter and
tighter and tighter until really there’s almost
no space in the middle left. And that’s how I’m going
to draw it fizzling out. So initially, they get
kind of more narrow and they get even more narrow
as the muscles in the walls tighten and tighten and tighten. And they finally get
something like this. And you still have
blood, of course, going to other branches,
which is what I’ve drawn here. But that last little
bit going just to the umbilicus, that part
is going to constrict down. And this process happens over
the course of a few hours. So now you have it. You have all the
five adaptations and how things change over
the course of minutes, hours, and days. And of course, it’s not exact
and each baby is different, but these amazing changes are
happening soon after birth.

100 Replies to “Baby circulation right after birth | Circulatory system physiology | NCLEX-RN | Khan Academy”

  1. One thing I would like to mention about the Foramen Ovale is that it may not close completely directly after birth. In fact, many infants will continue to have what will sound like a heart murmur upon auscultation, for a couple weeks after delivery until that Foramen Ovale completely fuses closed. This is normal and most doctors will be able to differentiate between a heart defect and this slow closing of the Foramen Ovale.

  2. OMG!!!

    Clamp is not physiological. It cuts off the oxygen supply to the baby, together with 1/3 of baby's own blood still in placenta, iron, red and white blood cells, and stem cells. There is a mounting evidence now for both preterm and full term babies how immediate clamping is the cause for anemia and mental retardation, ADHD, and whole host of neurodevelopmental delays. Please familiraize yourself before lecturing.

  3. I have been watching his videos since I started college in 2010. I am now 3 months away from graduating as an RN (registered nurse) and I am still using his videos. He is absolutely amazing!!!!!!. I always recommend his videos to everyone. Thank you so much for your fabulous videos, you have no idea how much they have helped me, exspecially through all my Biology's.

  4. Can you shed light on "fad" births that leave placenta attached for 24 hours or so? I can wrap my head around why some midwives wait until the baby is breathing and the placenta detaches as a little extra "insurance" for well-being since there may still be enough oxygen-rich blood to do some good for the baby if there is a pulmonary problem. It seems that Wharton's jelly will shut off most flow pretty quick, therefore oxygen and prostaglandin will drop. Any point or risk in the fad?

  5. Thanks for the information! The video however skips the most important bit of information parents need, namely that at the moment of birth a third to a half of the baby's blood is in the placenta, and that the CORD MUST NOT BE CLAMPED until this blood has been transferred to the baby and the cord stops pulsating and goes flat and white. It's in fact best to not clamp the cord until the placenta has been delivered. Once the blood has been transferred the placenta goes flat and is more easily expelled than a placenta which is full of blood due to premature cord clamping  which deprives the baby of its full volume of blood, leaving the baby weakened and anemic,

  6. Why do you teach the intervention of clamping in a video attempting to explain human anatomy and physiology. Cord clamping isn't physiology.

  7. Thanks for the video, great stuff, and thanks to Erwin for bringing that important point, I did not know that. You guys rock! Thanks.

  8. ?? because performed immediately at birth it is a surgical intervention, shown to reduce blood volume, produce bradycardia, risk ID anaemia..besides, it would be more interesting to see an accurate presentation of transition from placental to pulmonary respiration that isn't just 'clamp'.

  9. Does the pressure and resistance of blood flowing through the left ventricle increase? If so, why is there an increase? 

  10. Great video. I have a question: when the ductus arteriosus and the umbilical arteries constrict due to high pO2 and low prostaglandin levels, what eventually happens to them? Do they remain there as a cylindrically oriented cell mass, or do they apoptose?

  11. Thanks for the great video. Totally helped me as for my Reproductive Bio course. Am currently a Medical Sciences student. Cheers!

  12. I've been so lost with this fetal circulation before and after birth! Thank God, I stumbled onto this video, and the light bulb in my little brain is ON baby!!! thanks Khan!!!

  13. with the body's own production of wharton's Jelly, I really dont see the need for us to cut the cord or clamp it before this process happens on its own! more reason to delay cord clamp!

  14. Thank you!! 3 years in nursing school and nobody has been able to explain this as clearly as you in your video. You made fetal circulation feel easy!

  15. Wonderful indeed! The only thing I do not agree with: you say mother nature. Yes, nature in itself is amazing but our body was created…. we cannot claim that the heart or the liver decided something in the real sense of the word. As said… fearfully and wonderfully made! Thank God! And thanks for the explanation!

  16. I love this video. "So, this arteriole is excited, its never really had a chance to be dilated before…"

  17. every day in med university, my believe in one God increases. áll this system is impossible by nature it self. I can believe in adaptation but to some limit, There is bigger and genius power behind all this that make it happened, and I call it God. The creator of everything.

  18. Please please please dear god do a video on development of the heart. Preferably before my undergrad finished in 2 years. Would really appreciate a good vid on that.

  19. I regret that this is complete nonsense about the adaptions of the baby during the first minute after birth. "Now it is separated from Mum and breathing on its own" This is a major part of the adaption. How did it get separated from the Mum ?? Was it by a cord clamp ?? When did nature start using a cord clamp. Of course she never did although she does have a mechanism to close off the placenta but this is done slowly and after the lung function has been established. the first thing that happens after a normal healthy birth is the baby takes its first breath, this leads to a marked increase in blood flowing through the lungs and the blood leaving the lungs is not oxygenated. It is the oxygenated blood and the cold and handling of the card that causes constriction of the vessels within the cord and this "clamps" the cord vessels, but only gently and slowly and the vein stays open after the arteries so that the baby gets most of the residual blood in the placenta to use to fill its lungs.

    www.hutchon.net/birmingham2013/

  20. Simplified and creative demonstration of all topics! Excellent videos! Very much recommended for understanding fundamental concepts! 👌👌👏👏

  21. What happens to the amniotic fluid that was previously inside baby's lungs? Do they cough it out/swallow it?

  22. Amazing job , very well simply explained and schematized, really thank you a lot ! keep on what you re doing, Much respect !

  23. This video was fantastic! I've read the chapter 3 times and it finally clicked when you explained it in this video! Thank you!

  24. I watched both the before and after videos and I am so thankful you took time to make them! When I was reading about it in the book I was completely lost and decided to give YouTube a try and came along your videos! The way you explained it was so comprehensible! THANK YOU THANK YOU THANK YOU!!

  25. Super nice video. Though I wonder why does increase in oxygen levels make the pulmonary arterioles dilate while it makes ducts arteriosus and umbilical arteries constrict?

  26. I thought the umbilical vein was only in the umbilical cord and not the fetus. So why would there be blood there if there it's in the cord?

  27. i clicked here to learn about how the placenta helps in the transition from womb to world. but number 1. remove the plcaenta. do you have nay idea how stupid that is??? why the fuck clamp the placenta right away? the placenta IS what facilitates smooth transition. you meds are BACKWARDS as fuck. ignorant actually. immediate cord clamping is the most counter-intuitive practice. years of rigerous medical training yet they cant even recognise the placenta job over their machines?? >:(

  28. Great video thank you! I'm still confused about the fluid in the alveoli. Does it get pushed out into the blood stream or the interstitial fluid?

  29. So the pressure on the left side of the heart becomes greater than the right side of the heart therefore the septum primum closes off but why isn't the septum secundum opening up? Wouldn't the greater pressure on the left side push it open?

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