Stages of embryonic development

The process of human embryonic development has 4 stages, and the time lasts 8 weeks. It begins with the meeting of male and female sex cells, their fusion and the formation of a zygote, and ends with the formation of an embryo.

What are the stages of embryogenesis?

After the fusion of the spermatozoon with the egg, a zygote is formed . It is within 3-4 days moving along the fallopian tubes and reaching the uterine cavity. In this case, a period of crushing is observed . It is characterized by strong intensive cell division. At the end of this stage of embryo development , a blastula is formed - a cluster of individual blastomeres, in the form of a ball.

The third period, gastrulation, involves the formation of a second embryonic leaf, resulting in the formation of a gastrula. After this, the third germinal leaf appears - the mesoderm. Unlike vertebrates, embryogenesis in a person is complicated by the development of the axial complex of organs - the rudiments of the nervous system, as well as the axial skeleton and, together with it, the musculature are laid.

At the fourth stage of the development of the human embryo, the rudiments of future organs and systems formed to this moment are segregated. Thus, the above-mentioned nervous system is formed from the first embryonic leaf, and partly the sense organs. From the second endoderm, the epithelial tissue lining the digestive canal and the glands in it are located. A mesenchyme forms a connective, cartilaginous, bone tissue, as well as a vascular system.

Because of what can the sequence of these stages be broken?

The stages of human embryonic development, presented in the table below, do not always go in the order in which it is necessary. So, under the influence of certain factors, mostly exogenous, the course of development of individual organs and systems may be disrupted. Among such reasons we can distinguish:

• violation of environmental conditions (temperature, chemistry, etc.);
• violation of interaction between individual cells;
• heredity.

This is not all the reasons that lead to a violation of the development of the embryo. There are so many of them that sometimes physicians can not pinpoint exactly what caused the embryonic development process to fail in a particular case. As a result of the fact that the stages of development of the human embryo break their sequence, anomalies occur, some of which can lead to the death of the embryo.