MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

BIOLOGY

CHAPTER 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.4. ONTOGENETIC LEVEL OF LIFE ORGANIZATION

1.4.3. Biology of Individual Development

Teratogenic Factors

Teratogenic factors, or teratogens (from Greek *teratos* – monster, prodigy) are environmental factors that disrupt Embryogenesis and cause Congenital Malformations. The process of congenital malformations arising is called teratogenesis, and the science of teratogens and teratogenesis is known as teratology. Teratogens are classified into physical, chemical, and biological.

Physical teratogens include ionizing radiation, high and low temperatures, and mechanical factors (pressure, vibration, mechanical trauma). Chemical teratogens include chemical substances (including certain medications): Folic acid antagonists (aminopterin), valproic acid, androgens, coumarin anticoagulants, retinol (in excess), lead, organic mercury compounds, tetracycline, thalidomide, trimethadione, alcohol, cocaine, and others. There are numerous Examples of how chemicals induce congenital birth defects. For instance, in Japan, many children were born with neurological symptoms resembling cerebral palsy. It was discovered that the fish consumed by the mothers of these children contained high levels of organic mercury compounds released as industrial waste into Minamata Bay, a condition that became known as Minamata disease. Similar incidents occurred in the United States when hogs were fed corn grain treated with a mercury-containing fungicide, and their meat was consumed by pregnant women. In the 1960s in Western Europe, over 7,000 children were born with amelia and meromelia (complete or partial absence of limbs) and Heart defects. It was revealed that the cause was thalidomide (a sleeping pill and anti-nausea medication) taken by the mothers during the Cytology/cytology/16.html">Early stages of Pregnancy (Fig. 1.88). Following this tragic history with thalidomide, legislative acts were passed in all developed countries requiring every new pharmaceutical drug to undergo animal embryo teratogenicity testing before clinical application.

A frequent cause of congenital malformations is maternal alcohol consumption.

The complex of these defects is described as fetal alcohol syndrome (narrow palpebral fissures, maxillary hypoplasia, cardiac defects, mental retardation). The incidence of fetal alcohol syndrome is 1-2 cases per 1,000 newborns. Even moderate alcohol consumption during pregnancy is harmful. Tobacco smoking also poses a serious danger.

Tobacco smoke components inhibit fetal development, lead to low birth weight and premature birth, and some act as teratogens. "Passive smoking" is likewise harmful: in families where the father smokes, developmental anomalies in children are recorded twice as often as in non-smoking households.

Biological teratogens are pathogens of infectious and invasive diseases (TORCH infections): rubella virus (rubeola), cytomegalovirus, Herpes simplex virus, varicella-zoster virus, *Toxoplasma gondii*, Syphilis spirochete, and varicella virus.

Thus, rubella virus infection can lead to cataracts, glaucoma, heart defects, and deafness. Cytomegalovirus causes microcephaly, blindness, mental retardation, and fetal death. Infection with *Toxoplasma* results in Hydrocephalus (Water on the Brain), cerebral calcifications, and microphthalmia (abnormally small eyes).

Certain maternal Metabolic Disorders (Diabetes Mellitus, phenylketonuria) also exert a teratogenic effect. The risk of congenital malformations in children born to mothers with diabetes mellitus or phenylketonuria is significantly higher compared to the offspring of healthy mothers.

The action of teratogens depends on: 1) the genotype of the mother and fetus; 2) the stage of development: most major malformations occur during the third to eighth weeks of pregnancy (the teratogenic period) when Organs are actively forming. However, the embryo remains sensitive to teratogens both before and after this window. Therefore, virtually no period of pregnancy is entirely safe from The impact of teratogens on the embryo and fetus; 3) the dose and duration of exposure to teratogens.

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Fig. 1.88. Thalidomide embryopathy as a consequence of exogenous factor exposure in a pregnant woman (thalidomide intake).