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Fetal structures in an adult

Find out what happens to those nifty fetal structures once we get older. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.

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Video transcript

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.