Embryonic period of development

The embryonic period of human development includes the time from the moment of fertilization of the egg and lasts until 8 weeks of pregnancy. Conditionally it is divided into 4 stages, each of which has its own peculiarities. Let's talk about them in more detail.

What are the stages of embryogenesis?

The embryonic period of development in humans takes 2 months - this is how long the processes of transformation of the embryo into the fetus last. As a result of this process, a body is formed that has practically the same morphological features as the adult organism.

At the first stage, a zygote is formed. It is formed as a result of the fusion of male and female sex cells. This period is quite short-lived. After it comes the stage of fragmentation.

During this period, intensive cell proliferation occurs. In this case, the cells formed by crushing were called blastomer. First a small accumulation of these cells is formed, which resembles a raspberry berry in its external form, and was called morula. With further fragmentation, the number of cells increases and the morula takes on a more rounded shape, the blastula.

After crushing, the next, the third stage of the embryonic period of the development of the organism, is gastrulation. It assumes the transformation of a single-layer embryo into a two-layered one, i.e. simply speaking - there is a doubling of the shells. In this case, the gastrula itself consists of 2 embryonic leaves, ecto- and endoderms. During the evolution of all living things, the process of gastrulation became complicated by the formation of an axial complex (a neural tube, axial skeleton, musculature), which is laid on the dorsal side of the embryo from the 3rd embryonic leaf.

The fourth period involves the isolation of the main rudiments of organs and tissues, as well as their further development. Along with this, there is an intensified unification of parts into a single whole. So, from the outer layer of the endoderm, the formation of epithelial tissue lining the digestive canal, as well as its glands. From the mesoderm - the muscles, as well as the epithelium of the genitourinary system, the serous membranes of the brain. A mesenchyme forms a connective, cartilaginous, bone tissue, vascular system.

How does the laying of the main organs and systems take place?

After listing all the stages of the embryonic period of development, we will also tell what systems and organs are formed on each of its weeks. Thus, the process of crushing during the formation of a human embryo lasts approximately 3-4 days. During this time, it moves along the fallopian tubes to the cavity. As a result of the process of crushing from blastomeres located on the surface, a shell is formed, which participates in the process of feeding the embryo, the trophoblast. Those blastomeres, which are located directly in the center, form an embryoblast, from which the future body of the embryo is formed.

Approximately from the second week of the beginning of the development process, the embryo is immersed into the wall of the uterus. At the same time, formation of such structures as yolk and amniotic vesicles is observed. After they form a mesenchyme, an amnion is formed. This is essentially an aqueous membrane that forms a bag, which is subsequently filled with all known amniotic fluid.

At about the 3rd week of embryonic development, a dense lump of growing cells is released from the back of the embryo. Its so-called head section, thickening, forms the primary nodule. It is this structure that gives rise to such anatomical formation as the neural tube.

At 4 weeks apart from the extraembryonic membranes, the embryo undergoes primary segmentation as a result of enhanced growth, i.e. separate segments of the future fetal body are formed. Parallel to this, the initial stage of the process of organogenesis and histogenesis takes place.

By the 5th week of pregnancy, the rudiments of the arms and legs can be clearly defined, and by the 6th week the limbs are divided into the main segments. Approximately by the end of 7 weeks at carrying out of US it is possible to see rudiments of fingers. So, at week 8 (this is how long the embryonic period lasts), the rudiments of the embryo organs complete.

In order to visualize the main stages of the embryonic period of development, let us present below the table in which they are displayed.