How is the development of the human embryo?
The entire period of embryonic development of the human body is usually divided into the main 4 stages. Let's talk about each of them separately.
The first stage is short-term and characterized by the fusion of germ cells, resulting in the formation of a zygote.
So, by the end of the first day from the moment of fertilization of the female sex cell, the second stage of development begins - crushing. This process begins directly in the fallopian tubes and lasts about 3-4 days. During this time, the future embryo advances to the uterine cavity. It should be noted that the human fragmentation is complete and asynchronous, resulting in the formation of a blastula - a set of individual structural elements, blastomeres.
The third stage , gastrulation, is characterized by further division, during which the gastrula is formed. In this gastrulation consists of 2 processes: the formation of a two-layered embryo, which consists of ectoderm and endoderm; with further development, 3 embryonic leaf - mesoderm - is formed. The gastrulation itself occurs by a so-called invagination, in which blastula cells located at one of the poles are inserted into the interior. As a result, a cavity is formed, called the gastrocole.
The fourth stage of embryonic development, according to the table below, is the isolation of the main rudiments of organs and tissues (organogenesis), as well as their further development.
How is the formation of axial structures in the human body?
As is known, approximately on the 7th day from the moment of fertilization, the embryo begins to be introduced into the mucous layer of the uterus. This is due to the release of enzymatic components. This process was called implantation. It is with him that gestation begins - the period of pregnancy. After all, not always after fertilization comes pregnancy.
After implantation into the wall of the uterus, the outer layer of the embryo begins the synthesis of the hormone - chorionic gonadotropin. Directly, his concentration, rising, allows you to know a woman that she will soon become a mother.
By week 2, a connection is established between the villi of the fetus and the vessels of the mother's body. As a result, the supply of a small organism begins to be gradually carried out through the bloodstream of the mother. The process of formation of such important structures as the placenta and umbilical cord begins.
For about 21 days, the embryo has already formed a heart, which begins to implement its first contractions.
By the 4th week of gestation, when examining the embryo with ultrasound, it is possible to distinguish the eye cavities, as well as the rudiments of its future legs and pens. The appearance of the embryo is very similar to the auricle, surrounded by a small amount of amniotic fluid.
On the 5th week, structures of the facial part of the embryo's skull begin to form: the nose and upper lip are clearly distinguishable.
By the 6th week, the thymus gland is forming, which is the most important organ of the human immune system.
At week 7, the structure of the heart in the embryo is improving: the formation of septa, large blood vessels. Bile ducts appear in the liver, the glands of the endocrine system develop.
The eighth week of the embryonic period of development in the table is characterized by the end of the bookmark of the rudiments of the embryo organs. At this time, an intensive growth of external organs is observed, as a result of which the embryo becomes like a small man. At the same time, it is possible to distinguish clearly the sexual characteristics.
What is post-embryonic development?
Embryonic and postembryonic development - 2 different periods in the development of any organism. Under the second process, it is customary to understand the time period from the birth of a person to his death.
Postembryonic development in humans involves the following periods:
- Juvenile (before the puberty process begins).
- Mature (adult, mature state).
- A period of old age, ending with death.
Thus, it is easy to understand what kind of development is called embryonic development, and which is postembryonic.