Teratogen PDF / PPT

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Poonam Patel
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Terms
TEROS- Monster,

TERATOGEN- An agent that can produce a permanent

alteration of structure or function in an organism exposed

during embryonic or fetal life

TERATOLOGY- Branch of science which studies the

mechanisms and patterns of abnormal development

TERATOGENICITY- the induction of malformation by

teratogens

TERATOGENESIS- the process by which congenital

malformations are produced in an embryo or fetus.

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SUSCEPTIBILITY TO TERATOGENESIS

DEPENDS UPON:

1. Genotype of the foetus and maternal genome

2. Developmental stages / time of exposure

3. Dose and duration of exposure

4. Specific ways in which a teratogen acts on the developing

cells

5. Manifestations of abnormal development – death, malformation,

growth retardation and functional disorders

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THE SENSITIVITY OF THE EMBRYO TO

THE TERATOGENIC AGENTS INCLUDE

THE FOLLOWING

❖ PRE DIFFERENTIATION STAGE: the embryo is not

susceptible to teratogens. The teratogens may either cause death

of the embryo by killing all or most of the cells or they may have

no apparent effect on embryo. Resistant strain ( 5-9 days ) of

gestation

❖EMBRYONIC STAGE- stage of intensive differentiation,

mobilization and organisation. Therefore embryo becomes more

susceptible to teratogens (10-14 days) of generation.

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1. HEREDITY

e.g.,

1)Cleft lip andpalate (orofacial cleft)

2)Syndactyly

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2.ENVIRONMENT
The main environmental factors are teratogens-

1. ALCOHOL

Birth defects occur in the children of alcoholic mothers

FAS- Fatal Alcohol Syndrome

2. DRUGS AND CHEMICALS

a) Ethanol

b) Retinoic acid

c) Tetracycline

d) Thalidomide

e) Streptomycin

f) Cigarette smoking
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3. IONIZING RADIATION

•Rapidly kills the proliferating cell

•Mutagenic agents

•X rays

•Microcephaly

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4. PATHOGENS

1) Rubella virus-german measles-Symptoms include problems with the

eyes such as cataracts, ears such as deafness, heart, and brain.

Problems are rare after the 20th week of pregnancy

2) Herpes simplex- herpes of the eye, herpes infection of the brain, and

neonatal herpes when it affects a newborn

 

5.MATERNAL DISEASE

a) DIABETICS

b)PHENYLKETONURIA

c)MALNUTRITION

 

6. HEAVY METALS LIKE MERCURY AND LEAD

Organic mercury causes neurological symptoms and

Lead can lead to abortion and growth retardation

 

Types of twins with teratogenic disorders

Double monsters-siamese twins

The twins are joined or fused together at certain regions of the body

I. Equal conjoined twins

II. Unequal conjoined twins

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I. EQUAL CONJOINED TWINS

SYMMETRICAL DOUBLE MONSTERS

BASED ON THE NATURE OF THE FUSION OF PART OF THE BODY

a) CRANIOPAGUS

b) THORACOPAGUS

c) PYGOPAGUS

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a) HEAD TO HEAD FUSION- CRANIOPAGUS

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b).CHEST TO CHEST FUSION- THORACOPAGUS

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c).RUMP TO RUMP FUSION- PYGOPAGUS

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II. UNEQUAL CONJOINED TWINS

➢Here growth is inhibited or normal differentiation fail to occur in

one of the twins

➢The smaller individual of a conjoined pair is called parasitic twin

➢ Normal part – autosite

➢ If the parasitic twin attached to autosite at:

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a. Jaws – epignathus parasiticus

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b.Thorax – thoracopagus parasiticus

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c. Rump – pygopagus parasiticus

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EMBRYOMATA

One kind of mixed tumours containing clearly differentiated
organs representing all primary germ layers

TERATOMATA

Any kind of mixed tumours with tissues or fragmentary parts of
organs derived from more than one germ layer but without normal
architecture arrangement.

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EXAMPLE: DERMATOID CYST

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MALFORMATIONS IN LEGS AND ARMS

a) SIRENOMELUS

Upper part of the body is normal but the lower part is like tail of fish.

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b) AMELIA

Both pairs of appendages fail to develop completely

 

c) PHOCOMELIA

Here hand and feet may be attached directly to the trunk due to
the failure of the limbs to elongate.

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MALFORMATIONS OF HANDS AND LEGS

a) POLYDACTYLY

Duplication of single digit

 

b) SYNDACTYLY

Developing digit

fail to separate

from each other

 

c) OLIGODACTYLY

Failure of development

of one or more digit

 

PERSISTENCE OF TAIL

Instead of

regression, tail

continues to grow

and persist even

in adult stage.

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GIGANTISM

Excessive production of growth hormone

 

DWARFISM

Deficiency in
production of
growth
hormone

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REFERENCES

I. Developmental biology- m. A subramaniam- page (149-

157)

II. Developmental biology – scott. F . gilbert – page (666-670)

III. Developmental biology – the fundamentals – M.G university