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Current time:0:00Total duration:11:53

Video transcript

before a baby is born there are a lot of adaptations that we see that allow the baby to take nutrients and oxygen form um and you know successfully get those nutrients and oxygen to the different cells that need them in the body so what I wanted to do is kind of draw out for you in one diagram all the kind of things that we see before birth these are all the things that are happening while the baby is still in the uterus sometimes we say in utero so before birth what do we notice well this structure over here this is our placenta this is you know partially mom and partially fetus so the placenta has moms blood kind of pooling in this area and the baby actually sticks its little capillaries inside of that pool of blood and you can see that the purplish blood is kind of going in and the reddish blood is coming out and essentially what I was trying to draw there is that oxygen is getting picked up so it's actually getting oxygenated and this blood as it's kind of reddish is joining into this blood vessel down here so this is kind of the smiley part of our sour face and this is our umbilical vein so those are umbilical vein is actually going to carry oxygen of blood back towards the liver area so let me actually just jot that name down umbilical vein and this is actually the first of the adaptations I was talking about so I'm going to make a little list of adaptations over here on the side just so we can keep track of what they are adaptations and the first one will be the umbilical vein so once the blood goes into the umbilical vein it has kind of a branch point you can see that it can either go to the right or the left and if it goes to the left it's going to enter the liver so if it goes kind of this way it's going to enter the liver and it's going to take awhile for that blood to come out on the other side because it has to go through all the little capillaries in the liver and then emerge on the other side but there is a shortcut so this shortcut let me just circle it here the shortcut is actually going to be right here so let me just make sure it's very clear what that shortcut is this is called our ductus venosus ductus venosus and the ductus venosus is basically going to allow blood to go from the umbilical vein through it so it's like a little tube so it is just like any other blood vessel it's going to go through it and on the other side it hits and meets up with our inferior vena cava so this is our inferior vena cava right IVC just for short and the IVC or the inferior vena cavas a large vein picking up blood from the right leg and also from the left leg so this is our left leg down here so the inferior vena cava meets up with the blood coming from the umbilical vein which is very oxygenated and so this blood I'm going to draw is kind of purplish now because it's kind of got some oxygen but it's not as rich as what was coming out initially from the umbilical vein because it mixed in with the IVC and that blood dumps into the right atrium so this is our right atrium on this side and simultaneously you actually have blood from the superior vena cava or SVC zart head and arm region draining down this way and this blood also kind of ends up in the right atrium so you've got this blood kind of mixing and now I'm going to draw it as kind of a deeper purple because it's mixed up blood now the second adaptation then let me just make sure I don't skip out on these this is the first one the second one would be the ductus venosus that I wrote up which is as I said kind of a shortcut from the umbilical vein over to the inferior vena cava now the blood is in the right atrium so it has a couple of options first it could simply go down into the right ventricle and some of the blood does that it just goes right down into the right ventricle and if it goes into the right ventricle it's going to get squeezed and once it gets squeezed it goes into the pulmonary artery this is my pulmonary artery over here and we know the pulmonary artery has a branch over to the lungs on both sides so we've got some blood going to one lung and some blood go into the other lung but remember once that blood kind of approaches the lungs we have to think about what's going on inside of the lungs so let me draw out what's happening then inside the lung so you've got these sacs air sacs that actually are not full of air right because when the baby is still inside of the uterus or when the fetus is in the uterus it's full of fluid so you've got these sacks full of fluid and going past them our little blood vessel so this is a little blood vessel and let's say this is an arteriole over here now if it's full of fluid that means there's not much oxygen so what ends up happening is that there's a process called hypoxic pulmonary vasoconstriction and what that means is that the alveolus literally tries to help constrict constrict the arteriole so the arteriole has some smooth muscle like this and because there's no oxygen the alveolus is going to cause that little arterial to basically contract down so it basically looks a little bit more like this and when it looks like that what we've essentially done is increase the resistance of that arteriole and if this is happening millions of times and millions and millions of alveoli then the entire lung is going to have a lot of resistance a lot of resistance in the lung at this point so if that's the case that there's a lot of resistance then a few things we have to kind of deduce from that the first is that if there's a lot of resistance then the pressure in the pulmonary artery remember this is our pulmonary artery right here these two should draw a little arrow to both of them the pressure in the pulmonary artery is going to go very high so these pressures are going to be high and that's simply because you've got a lot of resistance that you have to try to fight against so they have a lot of pressure and if there's a lot of pressure in the pulmonary artery just think back and think well where did that pulmonary artery come from it came from the right ventricle so for there to be forward flow of blood you better have a lot of pressure the right ventricle and then I could take the argument back and say well if you have a lot of pressure in the right ventricle then you must have a lot of pressure in the right atrium so you have a lot of pressure basically on the right side of the heart because of the fact that you've got a lot of resistance in the lungs so these pressures especially the right atrial pressure starts getting so high that it starts getting higher than the pressure in the left atrium and so you get a little bit of blood flow that starts going from the right atrium across that foramen ovale that allows right here that allows blood to actually go across it so this is our foramen ovale foramen ovale allows blood to go from one atrium over to the other and since blood can now go across you're going to see some of the blood continue down into the right ventricle but some of the blood will also kind of go across into here and that's actually quite useful because at the same time that you have blood going across you actually don't have too much blood coming back through the pulmonary veins and the reason for that again is because it's hard to get blood flow through the lungs because there's so much resistance there so you have a little bit of blood kind of coming in through the pulmonary veins and you get some blood coming from the right atrium now from the left atrium blood is going to go down into the left ventricle and it's going to get squeezed around into the aorta so now you get blood in the aorta that gets squeezed there or sent there from the aorta or from the left ventricle I apologize so the left ventricle is squeezing blood down into the aorta and the aorta is distributing blood all the way down now before I finish off showing you where the aortic blood goes let's actually make sure I don't forget my list over here my third adaptation then should be the foramen ovale foramen ovale sending blood from the right atrium to the left atrium and a fourth adaptation actually I've just kind of sketched out but I haven't talked about yet is right here so you actually have this little this little guy right here a little connection a little vessel you can think what is a vessel because blood flows through the between the pulmonary artery and the aorta so this thing right here is called the ductus ductus arteriosus ductus arteriosus so the ductus arteriosus allows blood to go from the pulmonary artery to the aorta and why would blood go in that direction in particular well remember the pulmonary artery again has very high pressures and the high pressures are because of the high resistance in the lungs so because of those high pressures blood of course goes from high pressure to a place where there's lower pressure usually and in this case it's going to go from the pulmonary artery over to the aorta so it's actually going to flow in this direction let me just draw a little arrow it's going to go flowing in that direction so ductus arteriosus is another another fetal adaptation so we've got four so far ductus arteriosus and this actually explains then why you don't get too much blood coming back through the pulmonary veins because a lot of the blood goes into the pulmonary artery trunk ends up going into the aorta actually doesn't even go into the lungs because the resistance is so high so now let's kind of wrap this up let's say blood is now down in the aorta as I said it's going to go into the legs and it's also going to kind of go into these internal iliac arteries so I've drawn these arteries here these are the internal iliac arteries and they're of course lots of branches off the internal iliac but the important branch that I want to point out right now is this one this branch this major one that I'm kind of sketching in this is actually the way I have a name for it we call this the umbilical artery so this is actually bringing blood back towards the placenta now why would so much blood go to the placenta and that's a fair question why doesn't it go you know there's a branch here that goes to the bladder there's a branch that goes to other places why is blood going into the placental branch or the umbilical artery why why so much well it turns out that the Senta and this is very clever actually has a very low resistance very low resistance so just as the lungs have a high resistance and they're kind of making blood divert away from them the placenta has a low resistance and it makes blood divert towards it so you can see now that this is a really ingenious kind of system we have these five adaptations umbilical vein the umbilical artery now we have the ductus venosus and we have the foramen ovale and the ductus arteriosus I don't want to miss out on any of them so we have five important adaptations here and this is how blood flows in the fetus