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Fertilization and Embryology


Okay, so that is, what we just covered is very high yield, knowing mitosis, knowing meiosis one and understanding oogenesis and spermatogenesis. Then next concept is the process of actual fertilization. It's been more and frequently tested. So I'll just go through some things. So an egg, there's just two layers that you need to know.

You need to know the outer layer is corona radiata, okay? So corona, like a crown. Easy to remember it's the outer layer. And the inner layer is the zona pellucida, all right? So the acrosomal process is the process when a sperm penetrates the corona radiata and is able to bind to the zone pellucida.

This triggers an acrosomal process where, basically, the acrosome of the sperm is able to digest some of the zona pellucida and eventually make it into the ovocyte. So acrosomal process, just some digestive enzymes are released and it makes through the zona pellucida. And the coritcal reaction happens once this ovum and this sperm in the ovum membranes fuse, calcium's released and you this fertilization membrane that's created around the ovum cell.

That's called the cortical reaction, again. When sperm and ovum membranes fuse, calcium's released and you have the formation of this membrane, okay? A lower yield topic. Embryology, back to higher yield. Indeterminate and determinate or not that big of a deal but we'll discuss some things that are very big deals.

So indeterminate cleavage is just when you have myotonic divisions and early embryo. And these divisions don't differentiate these cells into any specific type of cell. So they still maintain their ability to divide into anything. Versus determinate cleavages when divisions narrow down the type of cell into which the cell can develop.

So cell that was able to become anything divides and now has only become, able to become some kind of neural cell, and then divide again and is only able to become part of the central nervous system. It gets more and more specific in throughout determinate cleavage. Okay, you need to know, what happens in the embryo. So basically, fertilization occurs and then you divide, you have 2 cell stage, 4 cell stage, 8 cell stage, 16 cell stage.

They don't really have a name. The next set after 16 cell stage is called a morula. It's a solid ball of cells, okay? After the morula, you have what's called the blastocyst. It's as a blastocyst that the fertilized egg will implant into the uterus. Okay, so, while a morula is a solid ball of cell, a blastocyst is a hollow ball of cell, okay?

And it's hallow here and this is called, the hallow part is called the blastocael. And then there are group of cell called inner cell mass, okay? And then on the outside here you have the trophoblast, and that's why actually implants into the uterine wall, okay? So this inner cell mass. And then the final thing you go to after the blastocyst is what's called a gastrula, okay.

And this process of gastrulation is very important.

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