General embryology lecture for written and viva examination : Teratology : abnormal development

 

Teratology

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It is the study of abnormal development.

It is the branch of science that studies the causes, mechanisms, and patterns of abnormal development.

What do you mean by congenital anomaly?

Ans: it is a structural abnormality of any type that is present at birth.

There are four clinically significance types of anomalies

a)       malformation : occurred during organogenesis

                                caused by environmental & / or genetics

b)      Disruption: morphological alteration of already form structures due to destructive processes  . Example: amniotic bands

c)       Deformation : mechanical forces that mold a part of fetus. Example: clubfoot

d)      Dysplasia: abnormal organization of cells. Example: congenital ectodermal Dysplasia   

The causes of birth defects or congenital anomalies are ;;;

1.       genetic factors such as chromosome abnormalities

2.       environmental factors such as drugs and viruses

3.       multifactorial inheritance (both genetic and environmental factors)

• Genetic factors such as chromosome abnormalities: they are two types

a)       Numerical :i) trisomy – Down syndrome ( extra 21 chromosome ) Klinefelter syndrome (47XXY) ii) monosomy: Turner syndrome (45X)

b)      Structural abnormality: Prader willi syndrome, Cri-du-chat syndrome

• Environmental factors :

a)       Infectious agents: i) Rubella virus : Cataracts, heart defects ii) HIV : growth retardation

b)      Physical agents: X-rays: spina bifida, cleft palate

c)       Chemical agents: i)Smoking: growth retardation ii) alcohol : fetal alcoholic syndrome, mental retardation iii) thalidomide : limbs defects

d)      Hormones: maternal diabetes: heart & neural tube defects

• Multifactorial inheritance (both genetic and environmental factors)

Cleft lip, neural tube defects etc.

Principles of Teratology: ( capacity of an agent to produce birth defects)

1. Susceptibility
2. to teratogenesis depends on the genotype of the conceptus
3. Susceptibility to teratogens varies with the developmental stage at the time of exposure
4. Manifestations of abnormal development  depend on dose and duration of exposure to a teratogen
5. Teratogens act in specific ways on developing cells to initiate abnormal embryogenesis
6. Manifestations of abnormal development are death, malformation, growth retardation & functional disorders