Meet the placenta! | Reproductive system physiology | NCLEX-RN | Khan Academy
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Meet the placenta! | Reproductive system physiology | NCLEX-RN | Khan Academy


– [Voiceover] 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. This uterus is an organ and women have this organ. It’s a very, very strong
organ, 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 kind of 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, right, and the baby is actually
swimming in this fluid, for months at a time. 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? Let’s think about what those needs are. Let’s enumerate them. One of them is oxygen. How does a baby take in oxygen if it’s not getting it from the lungs? The lungs are actually full
of amniotic fluid, by the way. How is it able to get nutrients? Things like sugar, glucose, that it needs for energy. I’ll put example, glucose. Let’s think about waste. How does it get rid of
things like carbon dioxide? For us, it’s very easy, we just kind of 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? It turns out all of these kind of issues are obviously very important, and the mom and the baby
work together a solution. This is the first chance for mom and baby to really work together on something. The solution is something
called the placenta. You may have heard of the placenta. The baby actually sends a couple of vessels up to the placenta. These are little umbilical arteries. It also sends up an umbilical
vein to the placenta. The vein brings blood
back from the placenta. In all these vessels, all three of these, make what we call the umbilical cord. 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 gonna 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. That’s the umbilical vein. It’s got oxygen, that’s why I’m drawing it as red even though it’s a vein because it’s coming back to the heart, that’s why we call it a vein. And you’ve got umbilical arteries. These two actually don’t
have too much oxygen. That’s why I’m drawing them in blue, just to show that they’re low in oxygen. They’re called umbilical arteries because they’re going away from the heart. The umbilical arteries
and the umbilical vein look like this, actually they’re kind of 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 gonna redraw this, just to show you how I remember this. Sometimes it’ hard to remember if there’s one artery or two arteries. I think of the mouth as a vein, or a V. And I think of the eyes as two little A’s. 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. This is the overall picture, now I wanna 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. I’m gonna 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’ll be the uterine wall. Again, remember the uterine wall is a nice, strong, muscular wall. Let me label it so it’s clear. This is uterine, I’ll just call it uterus, the wall of the uterus anyway. On the insides you’ve got, actually I’m working from the outside in. Let me draw some of mom’s blood vessels. She’s got some blood vessels coming up like this, this
is a little uterine artery. 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. I’ll draw a couple of them. I’ll draw another
uterine artery over here, and I’ll draw one third one over here. Of course, they are many more than three but I just wanna give you the concept that there are some uterine arteries. There are also some uterine veins. Let me draw some uterine veins as well. I’ll draw one over here. These blue ones are the uterine veins, I’ll label this one over here. What they’re doing is they’re actually going through a layer of tissue. Let me draw in a layer of tissue for you so you see exactly what I mean. There’s a layer of tissue here, they’re going through it. This layer of tissue is mom’s tissue. I’m gonna label it mom’s tissue, or I’ll just call it mom’s. It looks a little bit, you have
to stretch your imagination, but it looks a little bit like a plate. 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. Actually, let me switch colors. This part is known as the basel plate. If you’re talking about the basel plate you’re talking about
this bit of tissue here, with the blood vessels,
the uterine arteries, and the uterine veins. Just to be clear, it belongs to mom. This is mom’s cells. Now we get into some really fun stuff. All these uterine arteries, they squirt out blood. They don’t go into any other vessel. They just squirt out
blood into an open area. Let’s say there’s a red blood cell here, this red blood cell literally could touch, physically touch a red blood cell over here. They literally could come up, and meet, and maybe shake hands. They could then go down the veins. This is really, really different from how we usually
think about blood cells traveling always within a vessel. Cuz here it’s kind of a pool. You have this circulation that happens because you have these red blood cells, as I’ve drawn them, kind of going up, into the middle, then circulating into the veins. You have this interesting circulation where you basically have blood coming up through the arteries
and down into the veins. The way I think about this, and you can maybe choose your own kind of analogy. But for me, I think of it a
little bit like a hot tub. The uterine arteries are
like the jets of water, coming up. The uterine veins are literally like the drains in the hot tub. It becomes almost like a
swirling pool of red blood cells. Importantly, these red
blood cells have with them oxygen, they have nutrients, so they have a lot of
the stuff that our fetus is interested in getting access to. Let’s switch gears, let’s
think about our fetus. Our fetus has got, we said a couple of umbilical arteries coming down. I also said that they’re coming down inside of this Wharton’s jelly, this umbilical cord of Wharton’s jelly. Actually what happens is that the vessels actually branch out and they split up. The uterine arteries, form lots and lots and
lots of little branches. I’m gonna draw them in for you. Let’s say that the branches
go all over the place. They go like this. Let’s draw five or six branches over here. Let’s draw some branches
down on this side too. We’ve got lots of branches
off the uterine arteries. They want access to the
oxygen and nutrients. Guess what they do? They just kind of push in, in fact, you have little cells here. I’m gonna draw some pushing in right here. You got little cells that I’m drawing in white, called trophoblast. They literally do this. They just kind of push in. These white cells are trophoblast cells. They’re good at invading. You could think of them as invading or if you wanna be less aggressive, you could think of them
as being just curious. These little fetus cells,
called trophoblasts, start pushing in. And within the trophoblast
is a little blood vessel. 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. Now what’s gonna happen through diffusion, is that oxygen is gonna go
into the fetus’ blood cells. So oxygen is going this way, as well as nutrients. Oxygen, nutrients go inside, then you have carbon dioxide leaving. So carbon dioxide actually goes into the pool of blood. 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 cuz, 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. Once that exchange happens, they continue to stay closed, and you get a little
capillary coming back. You’ve got capillaries coming back from every part of this. All of these have been
doing the same thing. Going inside of this pool of blood. It actually gets a little
bit 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. It comes back around, and you have the blue vessels going into each one of these finger-like projections. You have a lot of gas exchange happening. This would be maybe a
better way of drawing it but the concept is the same. You basically have all this wonderful diffusion happening. As a result you actually have nice, rich oxygenated blood returning to the baby. This is finally allowing
the baby to have access to oxygen and nutrients and get rid of its waste,
its carbon dioxide. Each one of these is
actually doing the same thing with red or oxygenated blood coming back. Instead of having two vessels, it all dumps into one
vessel down the middle. This vessel, as we already know, is called the umbilical vein. This is actually the umbilical vein. If we call the bottom one the basel plate, then, of course, you’re guessing that there must be some name for this. This, of course, has its name called the chorionic plate. This one, you can already tell, this has all the cells from the fetus, so this belongs to the fetus. 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 basel plate. Then you’ve got some shared tissue, or space, in here. 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. I think of the placenta then as the first time that mom and baby work together for a common purpose.

About James Carlton

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79 thoughts on “Meet the placenta! | Reproductive system physiology | NCLEX-RN | Khan Academy

  1. Ahhh, a Rishi video! Would be good if he started making videos again, his explanations were really clear and understandable

  2. Got a B on my lecture exam thanks to khan academy, i recognize this guys voice on certain videos and I've realized he gives the best explanations

  3. you are using blue for the arteries which usually represents deoxygenated blood so do the veins carry the oxygenated blood to the fetus in the placenta?

  4. thank you so much! super helpful and looking forward to videos on the fetus growth, trimesters, and more! thank you again!

  5. Thank you!! Is it beneficial to keep the baby attached to the placenta and just allow the umbilical cord to fall off on its own?

  6. thanks a lot ! You saved me from a big headache while tempting to understand all this ! Great explanations 🙂

  7. Good video though not bad on the term basal plate, I know it is technically correct though can be confused with the embryonic neural tube.

  8. Thank u for what u are doing! For all you videos, for hours of work and ton of diligence. The result is really great!

  9. i never understood what was written in those massive embryology books.. This one is a concentrate of all that stuff. Brilliant work guys

  10. I like the language and terminology. The whole process kinda gets me imagine every bit of it and get there to feel the placenta. Oops 😛

  11. In the video seems like placenta belongs to both mom and fetus. But in the faculty lesson professor told us "Placenta only belongs to fetus". Which one is true?

  12. Your videos are great, but I suggest if you made a brief conclusion of the whole video or this small lecture on one or two written slides that would be so beneficial for us to study

  13. The arteries (red) carry oxygen and nutrients away from your heart, to your body's tissues. The veins (blue) take oxygen-poor blood back to the heart. Arteries begin with the aorta, the large artery leaving the heart. They carry oxygen-rich blood away from the heart to all of the body's tissues.

  14. I’m giving birth to first baby in two months and this helps so much to know what ten heck is going on in there lol very interesting! Great explanation. Thanks so much!

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