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