hi everybody and welcome back to miss angla's biology class i am miss angler and in today's video we are going to be looking at the final installment of human reproduction gestation now it's important to know that in this video i'm not going to be looking at the stages of pregnancy but rather the development of an embryo into a fetus i'm going to look at the protective layers around the embryo as well as how do nutrients and wastes are exchanged between the mother and the fetus now if you're new here don't forget to give this video a thumbs up like and subscribe turn your notifications on because i post every tuesday and thursday another exciting announcement i have is many of you have requested for tutorship or one-on-one lessons with me or just more interaction more content from me and so i'm going to be launching my membership and my members only section on my youtube channel from the 1st of april in it there are going to be so many videos specifically targeted to grade 12s in preparing them for their final exams and making sure they get that distinction right let's get into the first set of embryonic layers and we're going to start off with the placenta a very very important structure it's a temporary organ which means that it only grows during a pregnancy it's the connector between the mother and the embryo that develops and it plays a really important role in secreting progesterone and it takes over from the corpus luteum you'll remember from our menstrual cycle video that the corpus luteum secretes progesterone now progesterone is exclusively used to maintain our pregnancy and so we need really high levels of it now in order to make the placenta we are going to use the corian to do that and so the corian over here is this sort of yellow layer that we can see sitting on the outside it's important it's the outside layer because now you'll see soon that i'm going to show you the amnion which sits on the inside of that but the corian sits just on the outside and it has a couple of different functions the first thing the corian does is it enables there to be a large surface area the bigger the surface area the more nutrients the more wastes can be exchanged it also has a villi now you'll remember back from your previous grades villi are those long finger like extensions and that grow out of cells well in this instance these villi are a little bit bigger but they grow out of the corian into the wall of the endometrium and it allows the corian to attach to the endometrium and eventually and very importantly it will form the placenta and you can actually see that by our network of blood vessels that are growing through this and that would have only been possible if we had had a villi then let's move on to what we call the yolk sac now in humans the yolk sac provides initial nutrients but the placenta takes over from this along with the umbilical arteries and veins it's not a very important structure later on in other animals like amphibians and fish the yolk sac is really important it's where we get most of its nutrients from but humans don't need a yolk sac because they are the viperous they are going to rely on getting their nutrients from their mother and so the yolk sac is almost like a secondary thing it's not too important we then go on to the amnion and the amniotic fluid so i'm going to start off with the amnion at the bottom here now please don't get confused between the corian and the amnion i know this diagram looks like they're pointing at the same thing but please look really carefully i want you to see that the amnion layer is labeling on the inside and the corian label line touches the outside and essentially what the amnion does is it is a layer that secretes the amniotic fluid this fluid that we see up here it's all this blue liquid sitting around our embryo and that particular embryo needs to be cushioned it needs to be protected it needs to be supported and the amniotic fluid also provides a buffer between temperature change so that doesn't get too hot or too cold on the inside and basically the embryo is floating in the liquid and it provides us like giant airbag so that there's no mechanical damage to the fetus now lastly on our list here is the umbilical cord now you'll notice that the umbilical cord is coming out of our embryo or our fetus over here and it attaches into its placenta now the purpose of our umbilical cord is a connector between fetus and mother and it contains two very important blood vessels it contains the umbilical vein which goes to the fetus and it contains a umbilical artery which moves away from the fetus now i'm going to elaborate more on that in the next slide so don't worry if you don't know the differences between those two and why the one is the vein and that one is the artery and what do they do because i will elaborate what's important to know for exams and tests on this particular section is you will need to be able to label a diagram like this you will need to be able to provide the functions for these layers but you won't be asked to draw this now i wanted to elaborate a little bit further about what's actually happening inside the umbilical cord and what is happening with those veins and arteries now i can guarantee you that there's going to be some question in your paper and your final exam is going to ask you about these veins and arteries and it's really important you know which one is which a lot of people get them confused because generally they think that arteries um are going away from the heart and veins to the heart or they've got oxygenated blood and deoxygenated blood and we get so caught up that we don't know which one is which and what's a little bit sneaky about these underlying veins and arteries is that they're actually opposite to the ones that we would see in an adult and so a nice way an easy way to remember these things is as follows so let's start off with the blood that's going to the fetus okay i want you to remember the following if it is going to the fetus then we say that it is a vein why do we say it's a vein if it's going to the fetus because remember the rule of a vein is veins carry blood to the heart and so what we see in our diagram here is this is the vein at the bottom here and the vein is carrying oxygenated blood it's carrying food it's carrying oxygen and so that is going to go into the fetus and it's going to go into towards its heart on the other hand i want you to think of artery i want you to think of a way arteries take blood away from the heart and so that means that this artery is going to go away from our fetus and it's going to take its waste products with it now yes that's very unusual because remember in your adult body arteries often have oxygenated blood and they have nutrients where in this case it's not it's not what's happening at the top of the diagram this is the artery and it's leaving see away so this is our artery up here and the artery is taking away the wastes from the fetus it's taking deoxygenated blood and wastes so now we're taking a u-turn here we're leaving through the umbilical artery up to the mother it's now up to the mother to do those exchanges now how do they ask us in an exam well generally they ask you what is the constituents of the blood like what does the blood contain does it contain oxygen does it contain wastes you need to know what are the components in the umbilical vein so what is in it oxygenated blood and food what is in the umbilical artery wastes and deoxygenated blood please know one more time that the vein goes to the embryo and the artery away now as always i like to do a terminology recap at the end of my lessons and you can use all of these words for your flash cards to study from you can turn these words into questions and all of this is great active recall for when you're studying for tests and exams so let's run through them very quickly we speak about embryos and we speak about a fetus essentially they're different stages of development an embryo is shortly after implantation within the first eight weeks if we're talking about a fetus we are talking about a much more advanced developed organism we're talking about nine weeks onwards this is when a um organism like a human starts to look more like a human maybe a few arms maybe a head at this point then we spoke about our amniotic layers and we started off looking at the corian now the corian is the outermost membrane it surrounds the amnion and it surrounds the embryo and it grows these chorionic villi and chorionic villi are there to provide a large surface area for attachment to the endometrium but also to exchange substances now that chorion and that chorionic villi eventually grow into the placenta they form the placenta and the placenta is a temporary organ and it's got a lot of important functions it assists in diffusing oxygen and food substances it assists in removing fetal waste maternal antibodies it's a barrier for protection against viruses and the most important thing it does is it secretes progesterone and that is the hormone that maintains pregnancy and it takes over that job from our corpus luteum we then moved on to the amnion and the amniotic fluid it is a layer surrounding the uh um fetus and it secretes the fluid and the fluid acts as a buffer it acts as a support system and it prevents any mechanical injury so that the fetus can just float in that liquid lastly we looked at the umbilical cord and the umbilical cord connects the fetus to the m to the placenta and inside that particular structure we find the umbilical artery which one more time remember is a blood vessel that's going away from the fetus whereas the umbilical vein is going to the fetus the umbilical artery is filled with deoxygenated blood and waste and the umbilical vein is filled with oxygen and nutrients now as always if you've liked this video don't forget to give it a thumbs up and subscribe and keep your eyes peeled for my announcement of my membership which will be the first of april you can look out for a video that's going to be posted very soon on my youtube channel explaining how memberships work and how you too can join i'll see you all again soon bye