Before determining how important the role and importance of the formation of blastula during the period of cell fertilization, it is worth considering the concept of fertilization. In this article we will give an exact definition of what a blastula is and what significance it has in the process of fertilization.
Fertilization is the process of fusion of the female and male gametes as a result of which a diploid cell called a zygote is formed. This is, in a way, the first phase of an embryo's life, usually taking two or three days.
Fertilization process
The fertilization process is a rather complex and mysterious mechanism. It consists of several stages:
- Blastula.
- Gastrul.
- Zygote.
- Neurula.
- Primary organogenesis.
- Prenatal development.
Definition of “blastula”
Of course, blastula occupies an important place in the process of fertilization, without which further development is simply impossible. What is blastula? We give a definition.
A blastula is a multicellular embryo that has only one layer of cells, which appeared during the blastulation process - the final stage of egg crushing. In other words, a blastula is an embryonic bubble or, as it is also called, a blastosphere.
In the process of crushing, the formed cells do not grow, but their number only increases rapidly.
Blastomeres are the cells of embryos formed during the fragmentation of a zygote.
The relative position of the blastomeres and their size vary depending on the method of crushing and the mass of the nutritional yolk in the egg. Here, in fact, what is blastula.
Blastula formation process
The crushing process is completed upon reaching the ratio of the volume of the nucleus and the cytoplasm.
In the process of zygote division, 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 ends 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 stage of development is called the blastula stage.
Crushing happens:
- complete and incomplete;
- uniform and uneven;
- synchronous and asynchronous.
The first blastomeres formed are different in color. They are more clarified, divide faster, enveloping the surface of the zygote, while in darkened blastomeres, this process proceeds more slowly, lining the internal embryoplast.
Upon reaching 107 blastomeres, the fragmentation of the human zygote is considered complete.
The composition and structure of the blastula
Having dealt with what blastula is, let us proceed directly to the question of the structure of the cell.
Depending on the type of fragmentation, the blastula varies in structure. A hollow-ball embryo is called a blastula.
If, as a result of crushing, a cavityless ball is formed, then such an embryo is no longer a blastula, but is called a morula. What exactly will happen 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 round in shape, only slightly flattened in places where they are in contact with each other. The free space formed between the blastocysts as it is crushed increases and, filling with liquid, turns into a blastocele. And in the case when the cytoplasm has a weak viscosity, on the contrary, the blastomeres fit tightly, as a result of which the fluid supply does not form, without acquiring a round shape. The blastula will ultimately depend on this.
So what is blastula? How is it formed? And what does it consist of? The blastula consists of a membrane having one layer of tightly fitting cells due to mutual pressure. By its histological properties, it represents the epithelial layer, called the plastoderm, which, subsequently, will turn into embryonic layers, flowing into the next phase - fertilization.
At the end of crushing, the blastula cell acquires the appearance and function of a blastocyst.
Blastocyst structure:
- trophoblast - a combination of light cells formed in the process of fragmentation, serves as a blastula membrane;
- embryoplast - a set of internal cells;
- blastocele is a cell cavity filled with liquid.
Blastula classification
The actual process by which a blastula is formed is called blastulation. The main purpose of which is the formation of an embryonic cavity. This is the final stage of zygote crushing, followed by the process of gastrulation.
Depending on the method of crushing, the following types of blastula are distinguished:
- coblastula;
- blastocyst;
- amphiblastula;
- discoblastula;
- blastodermic vesicle.
The origin of the term “blastula” is due to the Greek word biastos, which means “sprout” or “germ”, hence the meaning of the word “blastula” - a single-layer, multicellular embryo.