Conception occurs when the male sex cell (sperm cell) enters the female body and merges with its egg cell. As a result, a new cell (zygote) is formed and the formation of the human embryo begins. Only during the first eight weeks of intrauterine development, a baby is called a fetus or an embryo. In the future it is called a fruit.
In the first eight weeks, the main organs, both internal and external, are laid. By the appearance of the embryo, it is not yet possible to determine the sex of the embryo - it will become possible only after another two weeks.
Stages of development of the human embryo
Let us trace how the embryonic development of man occurs. At the time of fertilization, there are two nuclei in the egg. When they merge, a unicellular embryo is formed, in which 23 chromosomes of the father are added to the 23 chromosomes of the mother. Thus, the set of chromosomes in the embryo cell is 46 pieces.
Next, the human embryo begins to gradually move along the fallopian tube towards the uterus. In the first four days, the fission of the cells of the embryo occurs approximately once a day, in the future the cells begin to divide more and more rapidly.
All this time the uterus is preparing to take the fetus, its mucosa becomes thicker and additional blood vessels appear in it. Approximately on the seventh day after fertilization embryo implantation starts, which lasts about 40 hours. Vorsels on the surface of the embryo increase and grow into the tissue of the uterus. The placenta is created.
At the end of the second week, the length of the human embryo approaches 1.5 millimeters. Closer to the fourth week, the formation of most organs and tissues begins - rudiments of cartilage of the skeleton, bones, kidneys, intestines, liver, skin, eyes, ears appear.
By the fifth week the length of the embryo is already about 7.5 millimeters. With the help of ultrasound at this time, one can observe how his heart is shrinking.
Beginning with 32 days, the human embryo has the rudiments of the hands, and a week later - the rudiments of the feet. When the 8th week of development ends, the embryo acquires a length in the region of 3-4 centimeters. Both the internal structure of the embryo and its external appearance acquire all the signs of a person. The tabulation of all the main organs ends.
Factors affecting the development of the embryo
Smoking
Nicotine can easily strangle the baby in the womb, because the fetus in the first two months is extremely sensitive to lack of oxygen, and when smoking it is inevitable.
Alcohol
The influence of alcohol on the development of the embryo is no less negative. For example, drinking at the time of conception can lead to an alcoholic embryo syndrome, which is expressed in multiple developmental anomalies. It is extremely dangerous even episodic use of alcohol, if it occurs at the time of implantation or the formation of an organ. The development of alcohol syndrome is caused by the effect on the embryo of ethyl alcohol, resulting in a slowdown in body growth, a violation of the CNS, anomalies of the face and internal organs.
Drugs
The effect of drugs on the fetus is manifested in the slowing down of development, multiple developmental defects, congenital nervous disorders, intrauterine death. There are often stillbirths caused by the cessation of drug intake in the child's body.
Radiation
The baby's embryo is extremely susceptible to the effects of radiation. Irradiation of the mother before the onset of implantation of the uterine wall, entails the death of the embryo. If harmful radiation affects the period of embryogenesis, anomalies and developmental anomalies develop, the probability of its death increases.