Crushing of the zygote

The concept of the "birth of a new life", as a rule, is limited only by associations about the conception of the child as a result of a passionate meeting of the egg and sperm. Further, according to the majority, pregnancy occurs, the fetus develops and a large belly grows in the future mummy. What is there to be wise, everything is trite simple ... In fact, prenatal development of a person is a very important and delicate process, requiring in-depth study. Let's try to understand the subtleties of one of its stages - the fragmentation of the zygote.

Zygote is a fertilized sperm ovum. It is with fertilization, which can occur within 3 days after sexual intercourse, the intrauterine development of a person begins. As a result of penetration of the spermatozoon into the egg, their nuclei merge with chromosomal sets of 23 paternal and 23 mother chromosomes and a nucleus is formed with the entire set of 46 chromosomes inherent in all cells of the body, excluding genital cells. After this, the zygote is crushed.

The fragmentation of a human zygote is a 3-4-day process of dividing an embryo into small parts of a cell by reproducing their structure in a manner similar to the structure of the mother cell (mitosis or fission by cloning type) while maintaining its overall size (about 130 μm). Blastomers - the cells formed during the fragmentation of the zygote, also divide, and at different rates, in other words, their division is not synchronous.

As a result of the first division of the zygote, there are two differentiated blastomeres. One, larger, "dark", is the basis for the development of tissues and organs of the embryo. The set of large blastomeres obtained in subsequent divisions is called the embryoblast. The second, small and "light" type of blastomer, the division of which occurs faster, forms a set of similar ones - the trophoblast. With its help there are finger-like villi, necessary for the subsequent fixation of the zygote to the uterine cavity. Blastomeres, without interacting with each other, are held with the help of only the shiny shell of the egg. Its rupture can lead to the development of genetically identical embryos, for example, identical twins.

The appearance of a multicellular embryo

As a result of the fragmentation of the zygote, a multicellular embryo is formed, consisting of the cellular layers of the embryoblast (inside) and the trophoblast (periphery). This is the stage of morula - the period of embryonic development, in which there are up to a hundred cells in the bud, crushing and the formation of which occurs as the embryo moves along the oviduct into the uterine cavity. In view of the lack of independent mobility, the movement of the crushed egg takes place under the influence of the hormones of progesterone and estrogen due to the peristaltic musculature of the oviduct, the movement of the cilia of its epithelium, and also the movement of the gland secretions in the fallopian tube. Somewhere on the 6th day after fertilization, getting morula into the uterus leads to the beginning of the blastulation process - the formation of a blastocyst, which is a hollow vial filled with liquid from the well-developed layers of trophoblast and embryoblast.

Approximately on the 9th-10th day, the embryo (implantation) of the embryo grows into the wall of the uterus, which is already in the complete environment of its cells. From this moment the woman stops the menstrual cycle, and you can determine the onset of pregnancy.