Many blastula, is slightly off-center, but this

Many animals develop very similarly.

If you were to look at how many seemingly unrelated organisms develop, you would find that the first basic steps of life are very close and almost exactly the same. Here, we will look at the process of gastrulation and how it occurs in frogs.

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What Is Gastrulation?

Gastrulation is when the three germ layers form around the embryo readying it for the next step, organogenesis, which is when organs are created.

When the sperm and egg combine, they form a zygote. As the days and hours progress, the zygote starts multiplying its cells until eventually it is a bundle of many cells. This then rearranges itself so there’s a hollow cavity inside of it. This is now called a blastula.

Gastrulation in frogs resembles closely the gastrulation of many other animals. We see the three germ layers forming just as they would in humans. In the end, we’ll see the process look very similar, if not the same, as the gastrulation process of human beings. So for the most part, once you get down the concept of gastrulation, you essentially understand it for most animals out there.One of the main differences in frogs over humans is that there is a larger amount of yolk-laden cells that are due to become the endoderm. These cells also end up forming a yolk plug.

Also, in frogs, the blastocoel, hollow space inside of the blastula, is slightly off-center, but this doesn’t make much of a difference in the gastrulation process.

The Three Germ Layers

At the end of gastrulation, we end up with a three-layered frog embryo. These three layers are the germ layers, which are the basis for all of the organs that will form later on.The outermost layer of the embryo is the ectoderm. This layer will become many different linings but most superficially will become the outer layer of the skin, part of the esophagus, as well as many other organs and nerve tissue.

On the inside of the gastrula is the endoderm, which forms the digestive tract of the embryo. The endoderm will become the digestive tract of the organism as well as a number of other assorted organs and linings, such as the lungs, liver, etc. The middle layer is the mesoderm. This ends up becoming many of the skeletal muscles of the organism.

This also becomes the bone, blood, and sex organs.This is just a quick overview of the three germ layers as they give rise to many different organs and organ systems. It’s also after gastrulation, when the organs form, that we see some of the major differences between organisms as they develop.

Gastrulation Process

But what about the actual process of frog gastrulation? The frog blastula will form a small invagination, or tuck, in its side.

This opening will eventually become the anus of the frog. The cells near the tuck start to get pulled inward further and further. These cells will eventually become the endoderm and mesoderm of the embryo.

At the same time this is happening, the cells that eventually will be ectoderm cells begin to stretch, multiply, and move towards the tuck, stretching over and covering the outside of the blastula.As gastrulation continues, the cells that got pulled into the frog blastula will arrange themselves so the innermost layer is the endoderm. On top of this is the mesoderm, which will exist in-between endoderm and ectoderm. The ectoderm is the outside covering that has stretched and pulled over the top of the other layers. The germ layers that form during gastrulation will arrange themselves on the outside, inside, and the middle of the newly formed gastrula, which is also called a three-layered embryo.

The endoderm also slightly pokes out of the gastrula in the form of a yolk plug. This yolk plug has lots of food cells in it, and eventually works its way inside of the embryo as organogenesis begins in the frog.

Lesson Summary

Upon fertilization of an egg cell by a sperm cell in a frog, a zygote is formed.

The zygote then begins to go through a few changes. The cells begin to pack tightly together to form a blastula or hollow ball. Next, a small invagination forms on the side of the frog blastula and begins to push into the center of the blastula. As gastrulation continues, the cells pushing inward become the mesoderm and endoderm layers.

The cells that cover the outside of the blastula end up becoming the ectoderm. By the end of gastrulation in frogs, we’ve got the gastrula, or three-layered embryo made up of the endoderm, mesoderm, and ectoderm.


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