what I have next to me is a real human fetus because one of the most amazing things about human anatomy and physiology is the story about how the body actually came to be because starting from one cell and developing all the way into a full body made up of trillions of cells is absolutely ridiculous and to help us with this story today we are going to show you the fetus so that we can talk about what it takes to get from that one cell at conception through some of the most vulnerable stages of development all the way up to becoming you so let's take a look at the fetus but let me quickly address the elephant or the lip in the room here I apologize if this destroyed lip of mine is a little distracting you're more than welcome to make fun of me for it in the comments below my friend Victor decided he wanted to show me how powerful and robust his deltoid and underlying greater tubric were when we were playing basketball the other night so you know what you can actually give him a little bit of grief in the comments too but anyway let's take a look at the fetus look how amazing this body is you can see development of the limb Anatomy the digits male genital structures and even the umbilical cord flowing into the placenta and isn't it remarkable that all of us were this small at some point while we were developing inside of mom but again what is even more remarkable is that we started even smaller than this this is an ovary and here is a test during the middle of the female sex cycle also known as the menstrual cycle ovulation takes place and during ovulation the ovary typically releases one egg or ovom sometimes a female can hyper ovulate and the ovary can release more than one egg and that is how you end up with something say like fraternal twins two separate eggs fertilize but most often one egg gets released every cycle with the average cycle being about 28 days what's also crazy to think about is that the ovm only lasts about 24 hours so a lot of my students when they first learn this they think okay well well how in the world does anybody ever get pregnant if you only have a 24-hour window well this is only part of the story because if you've ever watched our channel in the past you may know that I don't usually refer to sperm cells as just sperm cells I usually refer to them as pesky little sperm cells because those pesky little sperm cells can last 3 to 5 days in the FEMA reproductive tract so you can see how this would widen that window for pregnancy to occur now what is also interesting about the sperm and the oval them is that they are kind of just half cells and what I mean by that is they're considered half Ploy cells which means they contain half the genetic information or in other words the ovam and sperm only contain a single set of 23 chromosomes so in a way they're not a full cell with all the genetic information until the sperm fertilizes the egg which is then called a zygote and now you have a full diploid cell with 23 pairs of chromosomes or 46 total chromosomes and this is what is so so incredible to me and I'm obviously a bit of a nerd with this stuff but even after teaching anatomy and physiology for nearly 18 years and working with many patients over the years my mind is still just kind of blown that this actually works us starting as one cell and then that one cell has all the information it needs to become you to develop into nervous tissue creating your brain and spinal cord creating your bones muscles skin and your internal organs like your kidneys liver heart and everything else it really is a biological Marvel many people will also often wonder when certain structures or organs develop but it kind of depends on what you exactly mean by that because development is quite complex and things are developing simultaneously for example on day 18 or 19 the heart will start to develop and even start to beat by the end of the third week but it takes until about the seventh or eighth week for all four chambers to form and again since we're geeking out about all this imagine this just a tin tiny miniaturized heart inside of the fetus because at this point this particular fetus would for the most part have a fully formed heart as we estimate he's about 26 to 30 weeks along just entering into that third trimester and we actually have another video about the details and the Mysteries surrounding this fetus and how he came into our lab and I'll link that at the end of the video but let me give you some important developmental points to consider for each trimester the first trimester is the most critical stage of development as this is when all the major organ systems start to form and because of this extensive and widespread developmental activity this is the trimester when the developing human is the most vulnerable to the effects of things like drugs radiation microbes or infections the second trimester is characterized by the nearly complete development of the organ systems and by the end of this stage the fetus like the one we have viewed today shows the majority of the distinctive human characteristics the third trimester represents a period of rapid fetal growth when the weight of the fetus doubles and during the early stages of the third trimester most of the organ systems become fully functional and let's also talk about the terminology that we use to describe human development the term fetus is sometimes disliked by people maybe it's just because of how it sounds or maybe it feels less human to some but it's actually just a very specific term to describe a stage in the human developmental process for example weeks 1 to8 are referred to as the embryonic period and we refer ref to that developing human as an embryo and generally people kind of think of embryo as a cute name but it's different for some with the term fetus but the fetal period is from weeks 9 to 38 and we refer to that developing human as a fetus and the fetal period ends when someone is born and then they call that human a neonate or a newborn and then there's terms like infant toddler childhood adolescent Etc so again we just have these terms to describe the human developmental stages I don't know if that helps help and admittedly it's not like I would walk up to my pregnant sister or pregnant friend and say hey so how's that fetus doing I still usually just say baby but in science classes and in the lab we try to use the terms that represent those stages in human development so hopefully that kind of gives you a little bit of a different perspective on the term because fetus actually just means Offspring the other thing I also hope is that this gave you some extra understanding for how amazing this process is and that it actually works properly most of the time and I also want to express how grateful we are to the people that are willing to donate their bodies to science and education so that we can appreciate our bodies and life even more and of course it wouldn't be an Institute of human anatomy video if I didn't get a chance to say how excited I am about one of my favorite lifelong learning tools and that is brilliant brilliant.org is an amazing interactive online learning platform for stem subjects and I really believe it is one of the best and most fun engaging ways to learn math science and computer Compu science I've been using brilliant for almost 2 years now and it has definitely helped me to refine and sharpen past skills as well as develop new ones I recently started one of their new lessons called exploring data visually which is all about analyzing and interpreting data from visualizing charts and graphs which has definitely been helpful for me plus brilliant is constantly adding more of these lessons each and every month so you'll definitely find lessons and courses that are applicable to you no matter where you are on your educational Journey so if you're interested in check checking out this amazing learning platform go to brilliant.org to start a free 30-day trial plus the first 200 people will get 20% off their annual subscription we'll also include that information and the link in the description below thanks for watching our crazy Anatomy videos everyone like And subscribe if you feel the need and of course leave some comments below let us know what you thought of the video and we'll see you next time