In this video, we're going to be finishing up talking about implantation, focusing on days 10 through 12 post-conception. So, you guys remember how in our blastocyst, we have that outer layer of cells, our trophoblast. We've talked about how it is developing during this time, and then our inner cluster of cells or the embryoblast is going to go on to form the actual embryo, and that structure is doing some development during this period. So around days 10 to 12, the embryoblast is going to actually separate from the trophoblast and go on to form 2 new structures. First up, it's going to form the bilaminar embryonic disc, and bilaminar literally just means 2 layers. So, this is just 2 layers of cells kind of in a disc shape, and I'll show you that in one second. And then, it's also going to go on to form the amniotic cavity, and the amniotic cavity is basically just a gap between the embryonic disc and the trophoblast.
So if you look at our image here, just like before, we are seeing the lumen of the uterus in that darker pink on the right and then we are seeing the uterine wall or the endometrium in that lighter pink on the left. And then we have our little blastocyst, and it has grown a bit since we last saw it. But just like before, this orange is representing our cytotrophoblast, and then this yellow, where you can see it's kind of projecting extensions into that endometrium, is our syncytiotroblast. And then we have our embryoblast here kind of on the inside of that. And you can see in this structure here, we have these 2 distinct layers of cells. We have a blue layer and a yellow layer there, and that is the bilaminar embryonic disc. That is the structure that will go on to actually form the embryo. And then over here in this kind of sky blue, that little pocket right there is our amniotic cavity. So our amniotic cavity, obviously, right now, it's just kind of a little pocket right next to that disc, but that will in time go on to help form that amniotic sac and the amniotic fluid. So it's going to begin to kind of envelop and enclose that embryo a little later in development.
Now around days 10 to 12, the endometrial cells are going to proliferate and actually cover the blastocyst, which will make it fully implanted. So you can see here we have these light pink endometrial cells are now completely covering the blastocyst. So it is literally inside of the uterine wall at that point and at that point, it is fully implanted. And around this time, the syncytiotroblast is going to begin to secrete human chorionic gonadotropin, much better known as HCG, and that is the hormone that we can detect on a modern pregnancy test. So if you think about the timeline happening here, this makes total sense. So if we just draw a quick timeline like week 1, week 2, week 3, and then week 4. So week 4 is when a woman would typically be getting her period. Right? And we have ovulation happen at week 2. Ovulation, of course, leads to conception. And at this point, we are about 12 days or almost 2 weeks post-conception, which would place us right about here. And so by the time a woman is going to be missing her period potentially and knowing that she should take a pregnancy test, then we would have those nice high HCG levels, which would be at a level high enough to be detected by modern tests at that point. Alright. So, that is our kind of final phase of implantation, and I will see you guys in our next video. Bye-bye.