Introduction to Human Development - Video Tutorials & Practice Problems
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concept
Introduction to Human Development
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4m
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Video transcript
Hey, everyone. And welcome to the human development chapter. In this video, we're just going to go over some basic terminology to kind of get us started. And we're going to begin with the term conception. And so conception is the moment when an oocyte is fertilized by a sperm cell. And you guys remember an oocyte is just a term for an immature egg. And so conception marks the beginning of development. Now throughout this course you're going to hear me referring to a conceptus. And a conceptus is just a term to refer to the developing offspring. And what's nice about this term is that it can refer to either an embryo or a fetus. So as you'll see in an upcoming video the terms embryo and fetus both imply something about the age of the conceptus, whereas conceptus is kind of a nice broad term that does not imply anything about the development happening. So it's kind of just a nice general term that we can use. And then finally, it's good to understand how we measure the gestational period also known as the prenatal period. And the prenatal or gestational period is just the time during which the development of that conceptus occurs. And so the way that we measure this is that it extends from the date of the mother's last menstrual period. So we're looking at the first date of the last menstrual or most recent menstrual period, and that is sometimes abbreviated to LMP, right up until birth. And so that's gonna be approximately 40 weeks long. So if you look down at our little chart here, we are looking at this green line where we are starting again at the first day of the mother's last menstrual period, extending all the way through until birth occurs and that time period is usually going to be about 40 weeks long. So that is the, traditional way that we measure gestational period represented by this green, arrow here. Now astute to viewers may have noticed, like, Hannah, you just said that conception begins when an oocyte is fertilized by a sperm cell. That's not the same thing as the date of the last menstrual period. What's up with that? Love that you're asking questions. Fantastic point. It is kind of weird. So basically, as you may recall, women typically ovulate about 2 weeks into their cycle. And so week 2 is usually the actual date of conception and when that takes place. And so at the moment of conception, a woman is already considered 2 weeks pregnant. So basically, this entire time from the 1st day of the period up until week 2, nothing is happening. There is no development occurring. That's just kind of empty space, there. And we use you may be like, well, why do we even do this? Good question also. We use the date of the mother's last menstrual period because women are much more likely it's much more noticeable the first day of your last period. So it is a pretty reliable date that women can report on and then we can usually estimate that ovulation would take place approximately 2 weeks after that date. So that is why we use the date of mother's last menstrual period. But this does mean you have to kind of think about it because that means that from the moment of conception through birth, this period right here represented by this, yellow arrow, that's gonna be approximately 38 weeks. So just to kind of put all that together, the traditional way of measuring pregnancy is a gestational period of 40 weeks long, wherein the first two weeks nothing is happening. There is no development taking place. The actual development of the conceptus is taking place over a 38 week period approximately. And so just so you know, this course, this chapter is going to be focusing on the 38 weeks of prenatal development, so the actual 38 weeks of development from conception until birth. So our day 1 is the moment of conception essentially. But do be aware of this of, of this discrepancy. Some textbooks will talk about the dates a little bit differently. Some professors will use different dates, so be aware of how your textbook and your professor talk about it, but those are the 2 kind of traditional ways that we think about that prenatal period. Alright. So that is our little primer for human development and I will see you guys in the next one. Bye bye.
2
example
Introduction to Human Development Example 1
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1m
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Video transcript
Okay. So this one reads, Judy takes a pregnancy test after realizing her period is one day late. When the test comes back positive, she immediately calls her OBGYN to set up an appointment. On the phone, she tells them the date of her last menstrual period and is confused when the doctor refers to her as already being 4 weeks pregnant. If you were the doctor, how would you explain this to Judy? So let's run through these choices and see which one is the best explanation for that. So a reads, conception typically takes place within 1 to 2 days of the menstrual period ending, so using the date of the last period is a pretty accurate marker. And that's definitely incorrect. Right? We know that for conception to take place, ovulation has to occur and ovulation will take place about 2 weeks after the period, not 1 to 2 days after it ends for most women. So, a is definitely not a very good explanation. B reads that important prenatal events like placenta development actually take place in the time between the menstrual period and conception, and that's also incorrect. We know that there is actually no development taking place during that time at all. We need conception for any development to actually begin. So b is not a good explanation either. C reads, we often measure pregnancy starting with the date of a woman's last period rather than the date of conception because reporting tends to be more accurate, which means that for 2 of those 4 weeks you weren't even pregnant yet. And that is a fantastic explanation. So we really do, we use that date of the last period because women are just much better at reporting it. Women typically don't know the day of ovulation, they usually know the day of their first, of their period beginning. So c is definitely a great answer. Then d reads it's impossible to accurately predict the day of conception so it's best to ballpark it and that's not true either. We have a pretty good way to estimate that date using the day of the last menstrual period. Alright, so our answer here is going to be c. And there you go.
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Problem
Problem
True or False (if false, choose the answer that would correct the statement): Conception is the moment an embryo begins to develop.
A
True.
B
False: Conception is the moment a person discovers they are pregnant.
C
False: Conception is the moment an oocyte is fertilized by a sperm cell.
D
False: Conception is the act of sexual intercourse.
4
concept
Timeline of the Prenatal Period
Video duration:
4m
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Video transcript
In this video we're going to go over a timeline of the prenatal period just to begin to introduce some vocabulary as well as talk about some of the major events that we're going to be covering in this chapter. So the prenatal or the gestational period is often divided into 3 stages. So first up is the preembryonic stage and that is spanning weeks 12 post conception and during the majority of this time we're going to be referring to the conceptus as a blastocyst. It is going to have a few different names a bit earlier in development but for the majority of those 2 weeks that we're going to be calling it a blastocyst. And you can see what a blastocyst looks like right there. Basically just a big old pile of cells at this point, still very early in development. Next up we have the embryonic period and this is spanning week 3 through week 8 post conception and during that time we're going to be referring to the conceptus as an embryo. And you can see, just in these images how the embryonic period is a time of very rapid development. So we're gonna start that period looking like this as a little trilameter or 3 layered disc of cells, and then we're going to kind of enter that more like tadpole y stage and then finally we're going to end that stage looking a little bit more distinctly human by that point And then we are gonna get into the fetal stage, which is going to span weeks 9 through approximately 38 or when birth takes place. Could be 39, could be 37, just depends on what that baby wants to do. And during that time we're going to be referring to the conceptus as a fetus. And as you can see from our image here, fetus looks pretty much like a little baby, albeit a very teeny tiny baby for the majority of those earlier weeks there. So you can see we kind of have a timeline up along the top here, kind of spanning from week 1 to week 38 of development. And then along the left side, we have this list of events that will be taking place, and these are listed here in the order that we're going to cover them in this chapter. So feel free to refer to this, as kind of like a map to let you know where you are in the chapter and what topics are going to be coming up next. So what these pink lines are referring to is basically when these events are taking place. So you can kind of tell what week each of these events is taking place by looking at these pink lines. And these solid colored pink lines are referring to major developmental events happening and then these striped lines are referring to some development taking place, but the majority would be happening wherever we see that solid pink line. So to kind of give you an idea of what we're gonna go through, we'll begin with fertilization, which of course is the very first event that's happening in week 1. Cleavage and blastocyst formation will also be happening in week 1. We will be talking about implantation, which is the process of the blast assist embedding itself into the uterine wall, and that is happening during our pre embryonic, development stage. We'll talk about the development of the extraembryonic membranes or membranes that develop outside of the embryo. That will begin in our preembryonic stage, but the majority of that growth is gonna happen during our embryonic period. We'll talk about gastrulation, which is basically the process of creating that little guy right there, and that is happening in the preembryonic and very early embryonic phase. And then we'll discuss organogenesis, which is the creation of organs that will be happening during our embryonic phase. We will talk about placentation. Placentation is the creation and growth of the placenta that is gonna begin very early in development around week 2 and that will span pretty much all of embryonic development. The placenta is usually functional by about 12 weeks, but then it will continue to grow a little bit throughout the fetal stage as well. And then we'll talk about organ development and skeletal growth, which as you can see, we'll see a little bit of that happening in our embryonic period, but the vast majority of that growth, of course, will be more in that fetal stage of development. Alright. So that is our timeline of the prenatal period. Again, feel free to refer back to this lesson to kind of see where you are, as you go through the chapter and what events are going to be coming up next or what events are happening during which week. Alright. See you guys in the next one. Bye bye.
5
example
Introduction to Human Development Example 2
Video duration:
42s
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Video transcript
Okay. So this one reads, at 10 weeks, a conceptus is commonly referred to as a what. So looking at our answer choices, I know we can immediately take out infant because we're only gonna be calling them an infant once they're already born, and we can take out blastocyst for sure because blastocyst, is a very, very early stage. That's like 1 to 2 weeks of development. So we're left with embryo and fetus. So remember an embryo is how we refer to a conceptus between 3 to 8 weeks of development and then a fetus is from weeks 9 to approximately 40 or whenever birth takes place. So, a 10 week conceptus is going to be referred to as a fetus and there you go.
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