Intrauterine development of a person is the period from the moment of formation of the zygote (fertilized egg) to the birth of a fully formed fetus, which is viable outside the uterus of a woman.
This period is called antenatal. It lasts 280 days. The following stages of fetal development are distinguished:
• initial period - characterized by crushing of a fertilized egg, the formation of a blastula and its implantation in the uterine mucosa. Fertilization occurs when the germ cells of a woman and a man merge, in which a zygote with a diploid genetic apparatus is formed. In this case, the sex of the child is determined by the chromosomes of the sperm, which fertilized the egg. So, if it contained the X chromosome, then a girl will be born, if U is a boy. The initial stages of crushing are in the fallopian tube. The implantation process is completed by fixing the fertilized egg in the thickness of the uterine mucosa, where its further development takes place;
• embryonic period - the formation of the embryo and the laying of its internal organs. The intrauterine development of the fetus at this stage is the process of gastrulation, in which three germ layers are formed. In addition, it is in this period that histo- and organogenesis takes place (tissues and organs are laid). The eight-week embryo already weighs about 4 grams. His features are outlined, legs and hands are formed;
•
fetal period - accompanied by further growth and development of the fetus, which is already called the fetus from the third month of pregnancy. In this period,
ossification nuclei form in the bones
, the skin becomes covered with a fluff, the
fetal heartbeat begins to be heard
, the woman feels its movements. The intrauterine development of the fetus at this time is characterized by intensive growth processes and tissue differentiation.
The final stage is childbirth. Their onset is triggered by the release of the hormone oxytocin, which is synthesized by the pituitary gland. This hormone provokes contraction of the muscles of the uterus, which leads to pushing the baby into the pelvis and birth canal.
It should be noted that the
intrauterine development of the fetus is characterized by individual critical periods in which there is an increased sensitivity of the embryo to adverse external factors. The first three months of pregnancy, as well as childbirth, require increased attention to the condition of the pregnant woman. With the influence of negative environmental factors at this time, the risk of developing various anomalies and deformities, as well as complications during childbirth or after, increases.
It should also be noted that the intrauterine development of the fetus is accompanied by the formation of a unique organ - the placenta, which allows you to bear children in the womb. It is an important way to adapt to environmental conditions. Its main functions are participation in the gas exchange of the fetus, its supply of nutrients and oxygen, as well as the secretion of hormones, which ensure the normal course of the entire period of pregnancy.