Placentation - Video Tutorials & Practice Problems
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1
concept
The Placenta
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2m
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Video transcript
In this video, we're going to be talking about the placenta. So the placenta is the site of oxygen exchange, as well as nutrient and waste transfer between a mother and a conceptus, and it is a temporary organ that is derived from both maternal and fetal tissues and it is delivered after birth. So the placenta is going to be producing hormones to support the pregnancy all throughout the entire gestational period. And so one of the first hormones that it begins to produce is HCG like we already talked about. So, like we mentioned, the production the production of this begins almost immediately around days like 10 to 12 post conception when that syncediotrophoblast begins to release HCG and then we can detect that on a modern pregnancy test. Now, the placenta will also be producing estrogen and progesterone, even placental lactogen, as well as a hormone called relaxin. And the production of these hormones will begin a little bit more slowly and their levels will fluctuate throughout the pregnancy. And we're going to have a whole video talking about the effect that these hormones have on the mother. So for now just know that the placenta is producing them. Alright. And the final term we're going to go over is placentation. So placentation is just the process of forming the placenta and, like we talked about, it begins during the implantation phase and it continues throughout the entire fetal period. By the time a placenta is, birthed, around 40 weeks, it's going to be between 1 to £2, so they get quite large. So what you see here is an image and this is how it would look if a baby in a placenta were birthed without the umbilical cord being cut. You can see we have the baby still attached to the placenta via the umbilical cord there. So we'll go ahead and label our umbilical cord and our placenta, and the placenta has a lot of blood vessels so it tends to be a similar color to, like, a liver where it's just, like, very, very, like, a rich deep red color. Alright. So that is our little intro to the placenta, and I will see you guys in our next video. Bye bye.
2
example
Placentation Example 1
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1m
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Video transcript
This example asks us which of the following statements best describes the role of the placenta during pregnancy? So let's run through them and see what we have. So a reads that the placenta encapsulates the developing fetus holding it in place within the uterine cavity and that is incorrect. The placenta basically grows up against the uterine wall. It does not encapsulate the fetus the way that the amniotic sac would, for example. So a is incorrect. B says that the placenta facilitate the exchange of nutrients and gases between the mother and the conceptus, and that is correct. That is a great definition of what a placenta does so our answer is going to be B. Looking at C, I can tell that it's incorrect because it refers to the placenta as a permanent organ and it's not. The placenta is a temporary organ that is birthed at the end of pregnancy And then looking at d, it basically says that the placenta is functioning during the first and second trimesters and then slowly dissolves within the uterine cavity and that is also incorrect. The placenta will stay fully intact throughout the entire fetal period, does not begin dissolving at any point. So our answer here is going to be b and I will see you guys in the next one. Bye bye.
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Problem
Problem
Which of the following hormones is NOT produced by the placenta at any point during pregnancy?
A
Human chorionic gonadotropin.
B
Relaxin.
C
Melatonin.
D
Estrogen.
4
concept
Placentation – Weeks 2-3
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3m
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Video transcript
In this video, we're going to go over placentation in weeks 2 3, so kind of the earliest stages of placentation. So, do you guys remember how during implantation the syncytiotrophoblast is going to be releasing those digestive enzymes and kind of breaking down the endometrium a little bit? Well, that process creates pools of maternal blood within the endometrium. And those pools of maternal blood are known as lacunae or intervillous spaces. And as all this is happening and development is continuing, cells from the embryonic disc are going to proliferate and create a layer of extraembryonic mesoderm. So if you look down at our image here, we're seeing a conceptus that's approximately, like, you know, 2 and a half weeks or so. You can see we're fully implanted within the uterine wall and we have our little embryonic disc over here and you can see we have that blue layer and that yellow layer and the mesoderm is kind of building up in the middle, so all these little red cells that are kind of building up and forming that mesoderm. Then we know that the term extraembryonic just means outside of the embryo. Right? So extraembryonic mesoderm are just mesodermal cells that form on the outside of the embryo there. So all of these, like, reddish pink cells are just mesodermal cells that are forming around the embryo essentially. And then just like we saw before, all of this yellow is our syncediotrophoblast, just like we've seen in previous lessons. That's kind of eroding that endometrium. And you can see how around that syncediotrophoblast we have all of these pools of maternal blood forming, so that is the lacunae. Alright. Now, over time the extraembryonic membrane and the syncytiotrophoblast are going to become a structure called the chorion. And you can kind of think of the chorion as like a pre placental structure that basically just surrounds the conceptus and it will go on to become the outer layer of the embryonic sac. So if you look at our image here, we are now pretty much calling the extraembryonic, mesoderm as well as that syncediotrophoblast that all of this is now considered the chorion and that, of course, is going all the way around the conceptus there. So that is our chorion. And then the chorion is going to go on to develop projections called chorionic villi, and those are going to essentially enter the lacunae and they are going to be the main site of exchange between the mother and the conceptus. So nutrient exchange, gas exchange, waste exchange, that's gonna be happening within these chorionic villi. So if you look at our image here, basically, these little extensions that are coming out of the chorion, those are the chorionic villi. And we are going to see much more mature versions of those coming up in our next video as we talk about placentation, a little bit later in development. So I will see you guys there. Bye bye.
5
example
Placentation Example 2
Video duration:
55s
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Video transcript
Okay. So which structure is primarily responsible for nutrient and gas exchange between the mother and the fetus? So that is, of course, going to be a placental structure because that is where all exchange between the mother and the conceptus takes place. So just knowing that, we can already eliminate c and d and so we're left with the chorion and the chorionic villi and the chorion is going to be kind of the outer layer of the embryonic sac. It's basically going to be surrounding the conceptus but the chorion itself is not going to be the structure that allows for the exchange that happens between the mother and the conceptus. That is going to be specifically those chorionic villi and those are going to extend into those pools of maternal blood and that is going to allow for that exchange of things like nutrients, waste, and gas. So our answer here is b, the chorionic villi.
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Problem
Problem
The chorion is made up of the:
A
Syncytiotrophoblast and lacunae.
B
Ectoderm and syncytiotrophoblast.
C
Extraembryonic mesoderm and syncytiotrophoblast.
D
Extraembryonic endoderm and syncytiotrophoblast.
7
concept
Placentation – Weeks 4-12
Video duration:
4m
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Video transcript
Okay. So let's finish up talking about placentation going through weeks 4 through 12 of development. So around week 4, the chorionic villi are going to develop and extend, blood vessels that will connect to the umbilical arteries and veins. And then in weeks 5 through 12, the endometrium is going to be undergoing massive changes at a cellular level to accommodate the pregnancy and placentation and we're not going to go over all of that in detail. There are kind of 2 main things that you should probably know. So first is that the endometrium that is beneath the embryo or away from the lumen is going to contribute to the placenta. So this will essentially become the maternal portion of the placenta, And then the endometrium that is toward the lumen or toward the cavity of the uterus is going to go on to surround the embryo and the amniotic sac. So if you look down here at our images, we are showing week 4 week 12 of development. So looking at week 4 first, just to kind of orient you, we are still fully implanted within the uterine wall there. The lumen or the cavity of the uterus would be in this direction and the uterine wall, kind of toward the myometrium would be over in this direction. You can see we have our little embryo inside of that amnion and a little early umbilical cord is forming there with these umbilical blood vessels. So those are the 2 umbilical arteries and the umbilical vein. Then you can see how we have these chorionic villi, which now have these fancy little networks of blood vessels within them, and those are nestled within these intervillous spaces filled with maternal blood all throughout there. And then we have our maternal blood supply depicted here. So just to give you kind of a little zoom in on what this would look like, we have this image here. So what we're seeing is the umbilical cord right there, the umbilical blood vessels, and then you can see how those are connecting to the blood vessels within that chorionic villi. And then that chorionic villi is, of course, embedded in that intervillous space full of maternal blood, and we've got the maternal blood vessels supplying blood to that space. And so essentially, all of this is the portion of the endometrium that is gonna be contributing to our placenta. So that is the maternal portion of the placenta. And then the chorionic villi is the, fetal portion of the placenta that is kind of jutting into that maternal portion there. And again, that is going to be the main site of all of our exchange between the mother and the conceptus. The nutrient, waste removal, gas exchange, etcetera, will be happening within those chorionic villi. And then one other thing to note here is that you can probably see pretty easily, the chorionic villi on this side, so toward the lumen, are much smaller than the chorionic villi over on this side toward the uterine wall. And that's because these guys are getting kind of flattened a little bit. So as the embryo grows and the, you know, the embryonic sac is pushing out, they're kind of getting squashed against the sac and this endometrial tissue. So over time, those will essentially flatten out, which we can see over here nicely. So what we are looking at over here in week 12 now is a cross section of a fully formed placenta. So by week 12, our placenta should be fully formed and should be acting as the, conceptus' main source of all of its nutrients, gas needs, oxygen exchange, waste removal, etcetera, And you can see how this side of the, placenta has basically flattened out completely. So we're looking at that here, this kind of orangey peachy colored layer and then we have the endometrial tissue here in pink that is completely surrounding the embryo and the amniotic stack there extending all the way out and around that conceptus. Alright. So that is placentation, and I will see you guys in our next video. Bye bye.
8
example
Placentation Example 3
Video duration:
38s
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Video transcript
So the placenta should be fully functional as the fetus' sole source of nutrient gas and waste exchange by what time frame? So we would expect to see that placenta be fully functional by about 12 weeks post conception. So our answer here is going to be d. From 6 to 8 weeks, we are still seeing some development of that placenta, growth of the chorionic villi, development of those blood vessels within the chorionic villi, but but by about 12 weeks we should see a, you know, a good maturation of that organ, to the point where it can act as the sole source of exchange between the mother and the conceptus. So our answer here is d, 12 weeks.