Different tissues and organs are formed in certain periods of embryo development. At the same time the embryo at the moment of maximum intensity of d

Critical periods of prenatal development [child, fetal]

Different tissues and organs are formed in certain periods of embryo development. At the same time the embryo at the moment of maximum intensity of development processes becomes very susceptible to environmental stresses. At that time the probability of a violation of the program becomes the highest, and, thus, these periods of prenatal development is called critical periods of fetal development.

First critical period (first two weeks)

It is believed that the first critical period of human embryo development occurs within the first two weeks. In this period the blastula forms. If a negative effect on the mother or fetus was strong enough, it often kills the embryo, and then eliminates from the body of mother. If the impact is not so much, by virtue of the fact that the cells at this stage are totipotent, embryo can fully recover and continue normal development. According to scientific data, the frequency of natural termination of pregnancy at this time is around 40% of all completed pregnancies. In these situations, woman usually does not even know that she was pregnant.

Second critical period (20-70th day)

The second critical period of prenatal development lasts from 20th to 70th day after fertilization. This is the time of maximum vulnerability of the embryo. And in general, the period of embryogenesis after implantation of the zygote in the uterine wall until the 12th week is crucial to child development. At this time, origin and formation of all the vital organs occur. Therefore, under significant impact on the developing fetus of unfavorable, the so-called teratogenic (from Greek “teratos” — “beast” and “genesis”) factors may cause various developmental abnormalities — deviation of the normal structure or functioning of organs that go beyond the norm of reaction. And it is not only a variety of physical defects of development, but also, often, physiological anomalies. Many developmental disorders are so severe that there is miscarriage. It is believed that miscarriages during the prenatal period are at least 10% of registered pregnancies.

After 12 weeks of development the embryo acquires a “human appearance” and from that moment already called a fetus. Fetal development period lasts from 12th week until birth. At this time, occurs the maturation of the body — the formation of new tissues and organs, and these processes are accompanied by the rapid growth of the fetus. Despite the fact that various factors may still have a negative effect on the prenatal development of the child, in this period they no longer appear as congenital disorders.

Third critical period (childbirth)

The third critical period is childbirth. This event in the life birthing child is fraught with injuries, especially of the brain that can lead to cerebral palsy. This disease usually manifests itself in early childhood and is characterized by movement disorders. Patients have paralysis, muscle weakness, loss of coordination, and involuntary movements. It should be said that cerebral palsy, as well as most other congenital disorders cannot be completely cured, like the flu or dysentery. An important method of rehabilitation of these patients, in addition to all kinds of drugs, is a therapeutic exercise. There should also be their social adaptation. Taken from http://worldofschool.org

Teratogenic factors

Teratogenic factors of prenatal development include: various endocrine diseases of the mother, especially diabetes; temperature or ionizing impacts; a variety of chemical substances — drugs and alcohol; some infections. Among infections, the most dangerous are by unicellular parasites — toxoplasmosis and rubella epidemic viral disease. The latter — is not dangerous disease that usually children get sick. If it infects woman in the first 12 weeks of pregnancy, then the baby may have congenital malformations, including the defeat of the cardiovascular system, eyes and hearing. After the fourth month of pregnancy, the risk of this disease is reduced to zero. In addition, if a woman was ill with rubella as a child, then a secondary infection is not threatened, because rubella virus has already formed a stable immunity.

One of the most well-known teratogenic substances is considered to be calming and sedative thalidomide. It was found that in the period from 1956 to 1962 of XX century, due to the fact that pregnant women were taking this drug in large quantities in a number of countries of the world were born from 8 to 2 thousands of children with congenital deformities. This tragedy has forced many countries to tighten the requirements for licensed drugs.

Questions:
  • What is the time of fetal development is considered the first critical period?

  • What can cause teratogenic substances effects in the first 12 weeks of pregnancy?

  • What is one of the main causes of cerebral palsy?

  • Why metabolic diseases or physiological disturbances that occurred in the period of prenatal development are almost not curable?