Before determining how great is the role and importance of blastula formation during cell fertilization, it is worth considering the very concept of fertilization. In this article, we will give a precise definition of what a blastula is and what significance it has in the process of fertilization.
Fertilization is the process of the fusion of a female and a male gamete resulting in a diploid cell called a zygote. This is sort of the first phase of an embryo's life, usually taking two or three days.
Fertilization process
The process of fertilization is a rather complex and mysterious mechanism. It consists of several stages:
- Blastula.
- Gastrula.
- Zygote.
- Neirula.
- Primary organogenesis.
- Prenatal development.
Definition of “blastula”
Of course, the blastula occupies an important place in the process of fertilization, without which further development is simply impossible. What is a blastula? Let's give a definition.
Blastulais a multicellular embryo that has only one layer of cells that appeared in the process of blastulation - the final stage of egg crushing. In other words, the blastula is the germinal bladder or, as it is also called, the blastosphere.
In the process of crushing, the resulting cells do not grow, but only rapidly increase their number.
Blastomeres are the cells of embryos formed during the crushing of the zygote.
The mutual arrangement of blastomeres and their size differ depending on the method of crushing and on the mass of the nutritious yolk in the egg. That, in fact, is what a blastula is.
The process of blastula formation
The cleavage process is completed when the ratio of the volume of the nucleus and cytoplasm is reached.
In the process of division of the zygote, two blastomeres are formed, then each new blastomere is divided into two daughter ones, and so on, until the number of blastomeres reaches 12-16 pieces. Usually this process is completed after the third day after fertilization, when the conceptus in the morula stage, leaving the fallopian tubes, enters the uterus.
When the blastomeres reach 64 pieces, a cavity is formed inside. A further increase in their number leads to the fact that the cavity increases, and all cells line up on the surface of the embryo in one row. This developmental stage is called the blastula stage.
Crushing happens:
- complete and incomplete;
- uniform and uneven;
- synchronous and asynchronous.
The first blastomeres formed are different incolor. They are more clarified and divide faster, enveloping the surface of the zygote, while in darkened blastomeres, this process proceeds more slowly, lining the inner embryoplast.
When 107 blastomeres are reached, the cleavage of the human zygote is considered complete.
Composition and structure of the blastula
Having de alt with what a blastula is, let's move on to a direct consideration of the question of cell structure.
Depending on the type of crushing, blastulas differ in their structure. The embryo in the form of a hollow ball is called a blastula.
If a cavityless ball is formed as a result of crushing, then such an embryo is no longer a blastula, but is called a morula. What exactly will come out in the process of crushing, morula or blastula, depends mainly on the viscosity of the cytoplasm. When the cytoplasm has a sufficiently high viscosity, the resulting blastomeres are rounded, only slightly flattened in places where they come into contact with each other. The free space formed between the blastocysts increases as it cleaves, and when filled with fluid, it turns into a blastocoel. And in the case when the cytoplasm has a low viscosity, on the contrary, the blastomeres fit tightly, as a result of which the fluid supply is not formed, without acquiring a rounded shape. This determines the final shape of the blastula.
So what is a blastula? How is it formed? And what does it consist of? The blastula consists of a shell that has one layer of tightly fitting cells due to mutual pressure. According to histological propertiesrepresenting the epithelial layer, called the plastoderm, which, subsequently, will turn into germ layers, flowing into the next phase - fertilization.
After cell cleavage is complete, the blastula takes on the appearance and function of a blastocyst.
The structure of the blastocyst:
- trophoblast - a collection of light cells formed in the process of crushing, serves as a shell of the blastula;
- embryoplast - a collection of internal cells;
- blastocoel - cell cavity filled with fluid.
Blastula classification
The process by which the blastula is formed is called blastulation. The main purpose of which is the formation of the embryonic cavity. This is the final stage of zygote cleavage, followed by the process of gastrulation.
Depending on the method of crushing, the following types of blastula are distinguished:
- coeloblastula;
- blastocyst;
- amphiblastula;
- discoblastula;
- blastodermic vesicle.
The term “blastula” owes its origin to the Greek word biastos, which means “sprout” or “embryo”, hence the meaning of the word “blastula” is a single-layer, multicellular embryo.
