201-Prenatal Development

This video is about the basics of prenatal development prenatal development of course starts with fertilization, which is the fusing of an egg and sperm there are some extraordinary images of this available on the internet on the left we have one these images which is an egg covered in tens of thousands or maybe even hundreds of thousands sperm who have made it through the vaginal canal chosen the appropriate direction to turn up either the left fallopian tube or the right fallopian tube because remember they don't know exactly where there might be an egg and then have found an egg in the fallopian tube oftentimes we think about this process as sperm driven the sperm is there to conquer the egg it triumphantly has made it and found the egg and then the first one to push through as the one who wins and gets to fertilize it and that's actually not really an accurate representation what truly happens is there are proteins on the head of each sperm and when they reach the egg they start to rub that head with those proteins on the side of the egg looking for the appropriate protein receptors that are covering the egg and if there's a matchup between the eggs protein receptors and the sperms protein than the egg actually opens and allows that sperm in and then closes off to all other sperm by changing the chemical makeup of the outside so that's how we end up with just a single egg fertilized by a single sperm so this fertilization process generally happens in the fallopian tube if there's an egg it's been ovulated a small number of days beforehand and is moving down a woman's fallopian tube if it meets up with sperm than the sperm have the opportunity to fertilize it if fertilization does occur we now call the fused sperm and egg cell a zygote and a zygote really is just a single cell fertilized egg there are three stages to the development process after fertilization the first is called the germinal period so after we have the fertilized egg or the zygote it basically starts dividing so that one cell turns into 2, 2 into 4, 4 into 8 et cetera et cetera we just have massive amounts of cell division and in this happens for the first probably 8 in 10 days after fertilization the germinal period is where we find something called totipotent stem cells each of these cells that you see here are essentially totipotent stem cells which is a designator that say it's a kind of stem cell that can turn into absolutely anything and that's true at this point because we have a bunch of cells that have the ability to become any kind of cell in the human body some will eventually become hair cells some will become skin cells some will become heart cells some will become toenail cells brain cells liver cells et cetera at this point they don't have their jobs yet they're just cells eventually though cell differentiation does happen and that's just the term we use to talk about cells getting their specific job so they differentiate and start doing something specific once they do that they can start to form the systems that will make up the human being so we move now into the embryonic period once this differentiation has happened and the systems start to form so on the left we see an embryo very early in this period and on the right we see an embryo that's a lot later towards the end of this period you can see that in the beginning you don't really look very human you look a little bit alien and have some characteristics like a tale for example that seem strange to us if you were to look on the internet for images of the embryos of other species you would find that those embryos look a lot like our own human embryos but slowly through cell differentiation and the building up of systems we start to build arm buds which we can kind of see in the middle portion of the middle image a portion that will eventually become an eye the circulatory system starts to come into place at some point the heart will start beating and that tail starts to get absorbed you can see the tail in the middle picture is much smaller than it is on the left that's because it's being absorbed and then on the right there isn't a tail anymore the hand and arm buds have grown to be more like actual hands and arms we're looking a little bit more human-like by the end of the embryonic period then in the fetal period the third and final period which is pretty much from 2 months up to birth we're very human-like just growing bigger so on the left we see a fetus who is probably towards the 2 to 3 month mark and is about the size of a person's thumb and on the right we see a fetus that's getting towards the end of the term which is forty weeks of development and he's pretty big and packed in the womb of course some babies don't make it to the 40 week term date and they're born early and we call these premature babies or preterm infants so preemies are something that our culture is dealing with because we have the ability to keep infants alive outside of the womb much better because of medical technology than we were able to do before and because of that we have to start worrying now about survival rate because of course have been infant is born to early they really aren't fully prepared to deal with the outside world they would like to stay fetus longer and be able to completely develop so not just in terms of size because you can see both of these pictures are very small babies but also in terms of developing things like fat so the infant on top the premature infant on the top has very very little body fat that's why it looks too skinny and long and kind of disproportionate to what a full-term baby would look like so the survival rates are approximately the following right now at about 22 weeks of development which again remember is barely over half because a full term would be 40 weeks the survival rate is fewer than 10 percent so very few babies that are born this early live because they're just not prepared one of the major problems is lungs lungs are one of the last things that develop so it's difficult to breathe if is your lungs aren't 6 working very well however if you can keep that baby in there just one more week the survival rate jumps quite significant up to 53 percent so sometimes women who go into preterm labor are on to bed rest in an effort to keep the labor from actually progressing to the point where a delivery will be required because if you can keep that fetus in there for just even one more week the survival rate is quite substantially higher at 24 weeks it's 67 percent at 25 weeks it's 82 percent and at 26 weeks it's 85 percent so still 26 weeks is quite early but the survival rate has jumped dramatically just in the four weeks from the 22 development and that has to do with things like development of the lungs of course things aren't just going on with the developing fetus there's things happening with the mom's body as well one thing that often times women are concerned about is weight change of weight gain so this is an approximate breakdown of what a woman is going to gain because of the various parts of her body and that fetus' body that are going to change during pregnancy so first she's going to gain about four pounds of extra blood volume quite a bit of that will come from her own blood volume because she needs to be able to carry more nutrition and oxygen some of it will come in the form of blood in the baby's system and in the placenta 2 pounds of extra uterus the uterine walls thicken to be able to maintain the pregnancy 1

4 pounds of placenta so the placenta again is the thing that connects the mom to the fetus and is the transmitter of nutrition in and waste out 18 pounds of amniotic fluid that is the fluid that the fetus is floating in within the womb Within the amnion 1 pound of breast tissue in preparation for breastfeeding 27 pounds of interstitial fluid this is fluid that is basically just the water within ourselves everybody already no matter what has interstitial fluid and when a woman is pregnant she gets More interstitial fluid which is why a lot of pregnant women experience swelling of the feet or the ankles or the lower legs especially towards the end of pregnancy because they have so much water essentially in their system That as they walk around throughout the day gravity pulls that water down and it collects in the feet and ankle area 5 to 10 pounds of just body fat are very normal for a woman to gain and then of course 7 to 7 and a half pounds of baby totaling 25 to 30 pounds so a typically sized woman should gain somewhere between 25 and 30 pounds during pregnancy this is gonna depend of course on things like your height and your build But regardless of your starting point there is a certain amount of weight that's healthy to gain not getting enough weight is problematic and gaining too much weight is also problematic the other contributing factor that the mom provides is the environment both outside of herself and what she consumes and puts into the womb so teratogens have to do with the latter teratogens or teratogens are harmful chemicals that could impact negatively the development of the fetus these are things like alcohol or tobacco or hard drugs or even things like caffeine there's some research that points to the increased likelihood of a miscarriage if a woman consumes a lot of caffeine but other factors are important to first does mom have any particular diseases that could harm her developing baby so for example if the mom was HIV-positive that would be of concern because there's a likelihood of being able to pass that on to the fetus and in some parts of the world were a lot of women are HIV positive this is a major concern there's also concerns about things like keeping women from handling kitty litter because kitty feces can contain A parasite called toxoplasmosis that can cause some problems Women of course should exercise while their pregnant just in general in life you should exercise but during pregnancy it's important to maintain a healthy body weight it's also important to help build up your strength and stamina because birthing Of course is a very challenging process and women who have stronger core systems or who have better stamina are gonna not struggle quite as much nutrition is key eating healthy whole foods lots of fruits and vegetables avoiding a lot of sugar or fat remember that developing fetus is laying down the very basic systems that they will live with for the rest of their life so being able to have enough of the appropriate nutrients to build those systems are important So you maybe have heard about for example about folic acid being really important for brain development prenatally and that's true so women should eat a lot of foods that have folic acid in them amongst other kinds of food of course stress has been shown to be able to impact the the developing fetus for example high high levels of stress there's less research that point to the problems associated with just general regular day-to-day stress that women who are experiencing extreme stress like the loss of a loved one Or maybe a loss of a job can sometimes pass that stress on to their developing infant because our body releases hormones and chemicals when we're stressed cortisol and adrenaline it's part of that fight or flight response and it's possible for those to pass through the placenta and impact the system of the fetus maternal age is important this is especially something to consider as women are having babies later and later in life because of the availability of things like fertility treatments so there's some concerns with propensity for particular disorders or diseases for example Down syndrome is more likely much more likely in women who are older than younger and finally prenatal development can be influenced by whether the woman has had previous births or not


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