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Summary Chapter 15 Teratogens - An Zwijsen - Developmental Biology
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Complete summary of H.15 Teratogens, An Zwijsen. Developmental Biology. good luck with the exam!
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15. Teratogens & birth defectsfigure from mythology on the left is in fact based on reality! There
exists a defect that results in a very comparable phenotype.
Goals
Table of contents
3% of all newborns have a birth defect and 10% of them they are due to environmental factors,
such as environment around mother but also environment in utero! Medication the mother takes,
infections of mother with fever, etc.
Birth defects
from top to bottom:
- Normal
- Malformation of the fetus due to
abnormal genome that leads to developmental defect(s)
- Disruption, here the DNA is all fine, but then something
happens that disrupts the developmental process. This
disruption can be physical, teratogen, medication.
- Deformation, here DNA is all fine, but for example the hips are
down instead of head giving the hips less freedom and there
may be compression of the hips which can cause a hip
deformation, physical! Because there is too little fluid in the
amniotic sac that leads to compression of the embryo. Or there is another physical event that
makes that a tissue is deformed. But in principle there is nothing wrong at the molecular level
with the fetus.
- Deformation can also happen close to birth or shortly after birth.
- Deformation can also be restored in some cases. For example, a hip dislocation. Or when it’s
a club feet due to a deformation in utero. Using correct physio-therapy we can restore the
deformation. And we then restore the birth defect.
, - Dysplasia, usually a very severe early problematic development. Tissues are undergoing
maldevelopment, not just one affected process. For example, NC cells that do not develop
properly.
Birth defects = congenital defects
1. Malformation
2. Deformation
3. Disruption
4. Dysplasia
Heritable (affecting the germ lineage) versus non-heritable (affecting somatic lineages) causes. Not
every variation in development causes defects or anomalies.
1. Malformation
A morphological defect in an organ/organ part/tissue or bigger
region of the body due to an intrinsic cause (chromosomal
or genetic abnormality) that affects patterning, growth, differentiation.
Abnormal genome
e.g. Down syndrome (trisomy 21)
2. Deformation
A deformation
is an abnormal
form or development
of a part of the body
due to an abnormal
mechanical
external force on the
fetus during its
development
in utero that results in abnormal growth or development of tissues. External from fetus perspective,
so in utero also external!
e.g. Clubfoot due to breech presentation or intrauterine compression, or hip dysplasia
3. Disruption
Normal development is impaired by a (sudden) exposure to an extrinsic factor that affects the normal
development.
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