Embryonic human development is a process which originates from a conception of the body and lasts for up to 8 weeks. After this period, the body forming in the womb is called a fetus. Generally the period of intrauterine development in humans is divided into 2 phases: embryonic, which has just been mentioned, and fetal — 3-9 month of fetal development. Let us consider in more detail the main stages of embryonic development and give at the end of the table that will facilitate understanding of this process.
How does the development of the human embryo?
The entire period of embryonic development the human body can be subdivided into 4 major stages. Explain each of them separately.
The first stage is short and is characterized by the fusion of gametes resulting in a zygote is formed.
So, by the end of the first day after fertilization the female sex cell, begins the second stage of development is crushing. This process begins directly in the fallopian tubes and lasts about 3-4 days. During this time, the future embryo moves to the uterus. It is worth noting that in humans the complete crushing and asynchronous, thereby forming uninstalling — a collection of individual structural elements of the blastomeres.
The third stage, gastrolyte, characterized by further division, in which forms a Papoose. Gastrulation consists of 2 processes: the formation of a double layer of the embryo, which consists of the ectoderm and the endoderm; with further development 3 is formed of embryonic leaflet — mesoderm. Gastrulation occurs by so-called intussusception, in which the cells of the blastula, located on one of the poles, vpaivaetsja inside. The result is a cavity, called gastrocele.
The fourth stage of embryonic development, according to the table below, the separation of the basic 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, is approximately 7 days from the moment of fertilization, the embryo begins to intrude into mucous layer of the uterus. This happens due to the release of the enzymatic components. This process is called implantation. It starts with a gestation — period of pregnancy. After all, not always after fertilization pregnancy.
After implantation in the uterine wall, the outer layer of the embryo begins the synthesis of the hormone — human chorionic gonadotropin. Directly its concentration, elevating, lets you know the woman that she will become a mother soon.
2nd week is the creation of links between the villi of the embryo and the maternal vessels of the body. As a result, the supply of a small body slowly begins to be carried through the bloodstream moms. Begins the process of forming such important structures as the placenta and umbilical cord.
Approximately 21 days the embryo has already formed a heart which starts to make their first cuts.
By week 4 of gestation during the examination the fetus using ultrasound can distinguish the eye socket, as well as the rudiments of its future legs and arms. Their appearance the embryo is very reminiscent of the ear, surrounded by a small amount of amniotic fluid.
5 weeks begin to form patterns of the facial part of the skull of the embryo: clearly visible the nose and upper lip.
For week 6 there is a formation of the thymus gland, which is the most important organ of the human immune system.
7 days a week there is a perfection of the structure of the heart in the embryo: the formation of partitions, the major blood vessels. Appear in the liver, bile ducts, is the development of the glands of the endocrine system.
Eighth week of embryonic period of development in the table is characterized by the completion of the laying of rudimentary organs of the embryo. At this time there is intensive growth of external bodies, with the result that the fetus becomes like a little man. While clearly it is possible to distinguish sexual characteristics.
What is the post-embryonic development?
Embryonic and post-embryonic development 2 distinct periods in the development of any organism. Under the second process is commonly understood as the time period from birth to his death.
Post-embryonic development in humans involves the following periods:
Thus, it is easy to understand what development is called the embryonic and postembryonic what.