Stages of embryogenesis. Periods of embryo and fetus development

The development of the human body begins with the very first day of fertilization of the ovum with the sperm. The stages of embryogenesis are counted from the moment of the beginning of the development of the cell, which subsequently forms the embryo, and from it appears a full embryo.

Development of the embryo fully begins only from the second week after fertilization, and starting from the 10th week in the maternal body, a fetal period is already taking place.

The first stage of the zygote

Absolutely all somatic cells of the human body have a double set of chromosomes, and only the sex gametes contain a single set. This leads to the fact that after the fertilization and fusion of male and female sex cells, the set of chromosomes is restored and again becomes double. The cell formed in this case is called a "zygote".

The characteristic of embryogenesis is that the development of the zygote is also divided into several stages. Initially, the newly formed cell begins to divide into new cells different in size, called morules. Intercellular fluid is also distributed unequally. A feature of this stage of embryogenesis is that the morula formed as a result of division do not grow in size, but only increase in quantity.

The second stage of

When cell division ends from them a blastula is formed. It is a single-layer embryo the size of an egg. Blastula already carries in itself all the necessary DNA information and contains an unequal cell size. This is already on the 7th day after fertilization.

After this, the single-layered embryo passes through the gastrulation stage, which is the movement of existing cells into several embryonic sheets - layers. First they are formed 2, and then a third appears between them. During this period a new cavity is formed in the blastula, called the primary mouth. The previously existing cavity disappears completely. Gastrulation allows the future embryo to clearly distribute the cells for the further development of all organs and systems.

From the first formed outer layer in the future, all skin integuments, connective tissues and nervous system are formed. The lower layer formed by the second layer becomes the basis for the formation of respiratory organs, the excretory system. The last, middle cell layer is the basis for the skeleton, circulatory system, muscles and other internal organs.

The layers are named in the scientific environment, respectively:

• ectoderm;
• endoderm;
• mesoderm.

The third stage of

After all the stages of embryogenesis have been passed, the embryo begins to grow in size. In a short time, it begins to represent a cylindrical organism with a clear distribution to the cephalic and caudal ends. The growth of the ready embryo continues until the 20th day after fertilization. At this time, the previously formed plate of cells, the precursor of the nervous system, is transformed into a tube, which subsequently represents the spinal cord. From it, gradually grow and other nerve endings that fill the entire embryo. Initially, the processes are divided into the dorsal and abdominal parts. Just at this time, the cells are distributed and further division between the muscle tissues, skin integuments and internal organs that are formed from all cell layers.

Out-of-embryo development of

All the initial stages of embryogenesis are parallel to the development of extra-germinal parts, which in the future will provide the embryo and fetus nutrition and support vital functions.

When the embryo has fully formed and exits the tubes, the embryo is attached to the uterus. This process is very important, since the proper functioning of the placenta depends on the life of the fetus in the future. It is at this stage that embryos are transferred during IVF.

The process begins with the formation around the embryo of the node, which is a double layer of cells:

• embryoplast;
• trophoblast.

The latter is the outer shell, therefore it is responsible for the effectiveness of attachment of the embryo to the walls of the uterus. With its help, the embryo penetrates into the mucous membranes of the female organ, implanting directly into their thickness. Only a reliable attachment of the embryo to the uterus gives rise to the next stage of development - the formation of a child's place. The development of the placenta is carried out in parallel with its separation from the litter. The process is provided by the presence of the trunk fold, which, as it were, repels the walls of the extraembryonic organ from the body of the embryo. At this stage of embryo development, the umbilical stem becomes the only connection with the placenta, which subsequently forms a cord and provides nutrition to the baby during the remaining intra-uterine period of his life.

It is interesting that the early stages of embryogenesis in the region of the umbilical stem also have a yolk duct and a yolk sac. In non-placental animals, birds and reptiles, this sack is a yolk of the egg through which the embryo receives nutrients during its formation. In humans, this body is formed, although it has no influence on the further embryonic development of the body, and in time it is simply reduced.

The umbilical cord has in itself blood vessels, through which the blood is transmitted from the embryo to the placenta and back. Thus, the fetus receives nutrients from the mother and outputs the products of metabolism. This part of the bond is formed from the allantois or part of the urinary sac.

The fetus developing inside the placenta is protected by two membranes. In the internal cavity there is a protein fluid, which is an aqueous membrane. In it, and swims the baby before his birth. This bag is called amnion, and its filling is an amniotic fluid. All these organs are enclosed in one more shell - the chorion. It has a villous surface and provides the embryo with respiration and protection.

Step-by-step consideration of

For a more detailed analysis of human embryogenesis, which is understandable for most languages, it is necessary to begin with its definition.

So, what is embryogenesis? This phenomenon is the intrauterine development of the fetus from the day of its fertilization to its birth. This process begins only after 1 week after fertilization, when the cells have already finished dividing and the ready embryo moves to the uterine cavity. It is at this time that the first critical period begins, as its implantation must pass as comfortably as possible for the mother's body and for the embryo itself.

This process is implemented in 2 stages:

• tight attachment;
• penetration into the thickness of the uterus.

The fetus can be attached to any part of the uterus, except the lower one. It is important to understand that this whole process is carried out for at least 40 hours, because only by gradual actions it is possible to ensure complete safety and comfort for both organisms. The place of attachment of the embryo after adherence is gradually filled with blood and overgrown, after which the most important period of the future development of the future person begins - embryonic.

The first organs of

The embryo attached to the uterus already has organs that resemble the head and tail. The very first after the successful attachment of the embryo develops a protective organ - the chorion. To more accurately imagine what he is like, you can draw an analogy with a thin protective film of a chicken egg, which is located directly under the shell and separates it from the protein.

After this process, organs are formed, which ensure further feeding of the crumb. After the second week of pregnancy, you can see the appearance of allantoic, or umbilical cord.

Third week

Embryos are transferred to the fetal stage only after the formation of the fetus, but already in the third week you can see the appearance of clear outlines of future limbs. It is during this period that the body of the embryo is loosened, the trunk fold becomes visible, the head is prominent and, most importantly, the own heart of the future baby begins to beat.

Power Change

The given period of development is marked and one more important stage. Starting with the third week of life, the embryo ceases to be fed by the old system. The fact is that the stock of the egg is being depleted by this moment, and for the further development of the embryo it is necessary to obtain the substances necessary for the further formation of the substance from the blood of the mother. By this time, to ensure the effectiveness of the entire process, allantois begins to transform into the umbilical cord and the placenta. It is these organs all the remaining intrauterine time that will provide the fetus with food and release from the products of vital activity.

FOURTH WEEK

At this time, it is already possible to clearly define the future limbs and even the places of the eye cavities. Externally, the embryo changes insignificantly, since the main emphasis of development is given on the formation of internal organs.

Sixth Week of Pregnancy

At this time, the expectant mother should pay special attention to her own health, as during this period the thymus gland of her future baby is formed. It is this body in the future, the whole life will be responsible for the performance of the immune system. It is very important to understand that the ability of her child to depend on her own independent life to resist external stimuli will depend on her mother's health. It is necessary not only to pay attention to the prevention of infections, but also to warn oneself of nervous situations, to monitor the emotional state and the environment.

Eighth seven-day

Only starting from this time limit, the future mother can find out the sex of her child. Exceptionally, at week 8, the sexual signs of the fetus and the production of hormones begin to be laid. Of course, you can know the sex if the child wants it and turns on the right side on ultrasound.

The final stage of

Starting from the 9th week of pregnancy, the embryonic period ends and begins fetal. By this time a healthy baby should already have formed all the organs - they just have to grow. At this time, the body mass of the child is actively recruited, its muscle tone is increased, the organs of hematopoiesis actively develop;the fetus begins to move chaotically. It is interesting that the cerebellum is not yet formed at this time, therefore the coordination of fetal movements occurs with time.

Dangers during development of

Different stages of embryogenesis have their weak points. In order to understand this, we need to consider them in more detail. Thus, in some periods, human embryogenesis is sensitive to infectious diseases of the mother, and in others to the chemical or radiation waves from the external environment. If there are problems in this critical period, the fetus will develop a birth defect.

To avoid this phenomenon, one should know all the stages of embryo development and the dangers of each of them. Thus, the blastula period is a special sensitivity to all external and internal stimuli. At this time, most of the fertilized cells die, but since this stage passes in the first 2 weeks after conception, most women do not even know about it. The total number of embryos that die at this time is 40%.The transfer of embryos with IVF is very dangerous at the moment, since there is a risk of rejection of the embryo by the mother organism. Therefore, during this period you need to take care of yourself as much as possible.

Transfer of embryos into the uterine cavity is marked by the onset of the period of the most vulnerable embryo. At this time, the risk of rejection is not so great, but from the 20th to the 70th days of pregnancy, all vital organs are laid, with any negative effects on the maternal organism at this time the probability of development in the future baby congenital abnormalities with health rises.

Usually by the end of the 70th day all the bodies have already been formed, but there are also cases of belated development. In such situations with the onset of the fetal period, there is a danger for these organs. In other respects, the fetus is already fully formed and begins to increase actively in size.

If you want your future child to be born without any pathologies, then watch your health both before and after the moment of conception. Lead the right way of life. And then no problems should arise.