Fertilization and Implantation

by Jason Amores Sumpter
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Hello, everyone. In this lesson, we are going to be talking about the process of fertilization or the creation of a zygote. Okay, so let's get into our lesson. And the process of fertilization commonly is also called conception. This is a very common term, especially for human beings. Now fertilization is going to be the formation of a zygote from the fusion of an egg and a sperm. And the way this is going to happen is the sperm is going to have to enter the female body, and then it's going to travel through the cervix, which, if you guys remember, is the opening to the uterus, and then it's going to travel into the ova duct. Now what are over? Duck specifically called in human beings in human females there, specifically called fallopian tubes. But they are also going to be called uterine tubes. These air both meaning the same thing. I just want you guys to know those terms as well. In case you are given those terms on a test, they mean the same thing. Fallopian tube, uterine tube over ducked all the same thing in a human being. Okay, And once the sperm enters the oval duct. There should be an egg there or an ove, um, and that is going to be fertilized by that sperm. Now, upon the sperm entering the of, um, it is going to complete my Asus two and then they are going to fuse their nuclei together to create a deployed nucleus or the zygotes nucleus. Okay, everyone. So this is going to be the process of fertilization, and it's not as easy as you may think. The sperm has to do a lot of work to actually fertilized this egg, and part of it is going to be because off the jelly coat that it has to fight through and all of these reactions, we're going to have to take place inside of the egg as well. So the first thing that the sperm is going to dio is is going to do sperm binding sperm binding is going to be the very first step of fertilization. And in this step, the sperm attache's to the jelly coat. So the jelly coat you guys can see is labeled here, and this is going to be this orange structure right here, that orange layer off the egg and this jelly coat is going to be made of glycoprotein, and it's gonna be this very thick, viscous structure that the sperm actually has to push its way through to even get to the plasma membrane of the egg. And this is gonna be a protective structure for the egg, and it's going to work. Thio eliminate a mass number of sperm actually getting to the egg because they have to do so much work to actually get to the eggs membrane. So sperm binding is going to happen in the sperm is going to attach to the jelly coat in mammals. The jelly coat is also called the Zona Pellucida. Okay, guys, just so you guys know, let me write that down for you. It's also called the Zona who lucida in mammals specifically. So in our eggs human eggs it's going to be called the Zona Pellucida, but jelly coats a little easier to say. So what's going to happen now is once the sperm actually bind the jelly coat, the Ark a zone or the ark is, um is actually going to open up. And the ark is, um is that cap on the end of the sperm or the head of the sperm, and it's going to open up and it's going to release these arcas own enzymes. So this is going to cause the arcas own reaction to begin the Ark Assam reaction is actually going to dissolve that jelly coat and allow the sperm to actually dig through the jelly coat and get to the plasma membrane of the sperm. So the next thing that's going to happen is the sperm membrane fuses with the egg membrane. So now that these membranes actually fuse, which you guys can see in this particular reaction right here now that these membranes air actually fused, they're actually going to stimulate another reaction toe happen. And that is gonna be the cortical reaction. And you guys can see all of these little structures thes little yellow circles here are gonna be cortical Granules, and they're waiting for a sperm to actually bind its plasma membrane with the eggs plasma membrane. And once it does that, it's going to begin this cortical reaction. As you guys can see, these yellow circles are actually diffusing into the membrane, and they're going to release cortical enzymes, which is actually going to change the chemistry off the membrane of the egg cell, and what this is going to do is it's going to ensure that no other sperm buying to this egg. So what is going to do is going to block Polly sperm E Polly sperm is going to be basically more than one sperm fertilizing one egg. And in most organisms, you don't want that because you have too much genetic material in that particular egg. Some organisms there are exceptions, but in US human beings we only want one sperm and one egg to come together because then you have the perfect amount of deployed genetic material. And you guys can see in this diagram here that the genetic material of the sperm is actually entering the egg. And then those two sets of genetic material refuse to make these zygotes genetic material. So that's a brief overview of how fertilization is going to happen. If you guys want more information about the details of the Ark is own reaction or the cortical reaction, and he talks about that whenever we talk about animal development. Okay, so let's go down and see what happens after the fertilization process has happened. What's gonna happen next? What's gonna happen next is the zygote is going to form, and it's going to start developing into the embryo into the fetus. Okay, so what's going to happen is this is thes. I go here, these I got is that first cell that is made by the fusion of the sperm and the egg, and it's gonna have two sets of chromosomes. But on the very first day, it's going to start dividing via the process called cleavage. Cleavage is a very specific type of division. It's not like most mitosis. Cleavage is where cells split without getting bigger, so they're going to say, Stay the same general size. And this is generally going to allow this dividing Zygo, this dividing embryo to move through the fallopian tube without being too big. So you guys can see the very second day cleavage is going to begin and make all of these particular types of cells. Now, do you guys know what this structure is called? Because it's no longer Caldas. I go. Once it starts having cleavage, this is going to be called a more Ula a memorial A is going to be a solid ball of cells. Now the Morial A is then going to undergo this process called compaction, and that's happening right here. And the cells are actually binding together via Desmond's OEMs and via tight junctions and their compacting together. And then they're going to undergo the process of differentiation where they become different cell types in the developing embryo, which will then develop into different tissue types and different organ types. But all of these steps right here are gonna be happening to the memorial. Uh, so in the first day, you're gonna have fertilization and the creation of a zygote. And then on the 2nd, 3rd and 4th day, sometimes the fifth day, you're going to have the production of the more ULA, and it is going to be developing and compacting and differentiating. And then, on the fifth or the sixth day, you're going to have the formation of the blast Ula. So this is going to be the blast, Sheila, and it's different from Memorial A because it's no longer solid. It's actually going to be, ah, hollow ball of cells. As you guys can see, it's gonna have this cavity, and this cavity is going to be called the blast. Oh, seal. And this is going to be a fluid filled cavity. And it can also be called the blast to see, like, cavity, as they call it here in this diagram. Now, this is a blast, Sheila. But whenever you're talking about a blast, Sheila that specifically found in mammals, this is going to be called a blast Assist. So this is specific to mammals. So our blast villas are called blast assists. Okay, but all organisms have blast jealous, okay? And this is a hollow ball of cells that forms from the cleavage of the zygote in the fallopian tube. And it's gonna have two types of cells I want you to know about. It's gonna have these inner cell mass or inner mast cells, and it's gonna have these trophoblastic cells. Now the inner mass cells or inner cell mass are going to become the fetus after they begin to divide and begin to form basically the baby. This is where the baby is going to come from, and then the trophoblastic cells are actually going to become the placenta and any other supportive tissue that is needed. So these trophoblastic cells they're going to be the ones that air here in this ring of cells. And then the inner cell mass are gonna be those cells that you see in red. So there are also different terms for this that I want you guys to know their different terms for the inner cell mass. They can also be called the Epi blast or the embryo blast. Hopefully, you guys can see that, um, the embryo blast. They're all the same thing. They're just different names for the same thing. So embryo blast. So these are all also the inner cell mass. They're the same thing now. The truffle blast generally only has that one name. Okay, All right. So that's going to be the basis of what's gonna happen in the first couple of days. So now what's gonna happen next is the process of implantation. And I really like this diagram here because it does show you where all of the processes that we just talked about actually occur. So you guys can see here. I'm highlighting in yellow. This is the ovary. This is where the egg is going to be made. And this is going to be where this follicle right here Reduce it are. Excuse me. The follicle actually produces the egg and releases it. So the oocyte is going to be the egg now. Actually, fertilization doesn't happen in the uterus. Most people think it happens in the uterus, but it doesn't. It's actually going to happen in the fallopian tube right here. We can see the sperm coming to bind with the egg, and then they are going to form the Zygo, which you guys see here. This one right here is showing that the two nuclei of the sperm and the egg er actually fusing together and then we're going to form the zygote. Now we're going to have the cleavage begin around, day to, and this is going to form the more ULA. And as the more Ula is dividing and it's differentiating and it's compacting, it is going to be traveling through the fallopian tube to the uterus. And then finally, in day 5678 and nine we're going to have the blast Ula actually implant into the wall of the uterus, which you guys can see right here. So this is the implantation off the blastocyst or the blast Sheila. And then this particular little mass of cells will begin to grow, begin to differentiate and form the entire fetus and the placenta as well. Okay, everyone. So that was our lesson on the process is off implantation and fertilization. Next, we're going to talk about child's birth and gestation.