Intrauterine human development - the period from the formation of a zygote (fertilized egg) to the birth of a fully formed fetus that is viable outside the woman's uterus.
This period is called antenatal. It lasts 280 days. The following stages of fetal development are distinguished:
• Initial period - characterized by the crushing of the fertilized egg, the formation of 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 that fertilized the egg. So, if he contained the X chromosome, then a girl will be born, if Y, then a boy. The initial stages of crushing take place in the fallopian tube. The process of implantation ends with the fixation of the fertilized egg in the thickness of the mucous layer of the uterus, where it develops further;
• 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 embryonicsheet. In addition, it is in this period that histo- and organogenesis takes place (tissues and organs are laid). An eight-week-old embryo already weighs about 4 grams. His facial features are outlined, legs and arms are formed;
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fetal period - accompanied by further growth and development of the embryo, 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 fluff, the fetal heartbeat begins to be heard, the woman feels his 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 provoked 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 said that the intrauterine development of the fetus is characterized by separate critical periods, during 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 them, increases.
It should also be noted that the intrauterine development of the fetus is accompanied by the formation of a unique organ -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 that ensure the normal course of the entire period of pregnancy.
