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30 Cards in this Set

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What is gestational age?
It is defined from the time of fertilization by embryologists and from the 1st day of the last menstrual period by clinicians.
What is the embryonic period?
It begins at the start of the 3rd week of gestation (5th menstrual week) and lasts through completion of the 8th week (10th menstrual week).
What is the "all or none" theory of teratogenesis?
In the first two weeks after fertilization, tertogenic insults cause cell death from which the pregnancy can either recover fully or be lost.
Why are the first two weeks after conception considered low risk?
b/c the conception does not have direct contact w/ the maternal circulation for 5 to 7 days after fertilization, differentiation does not begin until 14 days, and most structures before day 14 are extraembryonic.
When is the critical period for neural tube defects?
From day 15 thru 27.
What is the critical period of heart development?
From day 20 thru 50.
What is the critical period for limb development?
From 24-36 days after fertilization. Exposure before day 33 can cause severe anomalies; after day 33 causes absence of hypoplasia of thumbs.
What specific environmental teratogens can cause limb anomalies?
Thalidomide exposure.
What is amelia?
Absence of the limbs.
What is meromelia?
The partial absence of a limb.
What accounts for the majority of developmental defects in humans?
Chromosomal alterations and genetic disorders (25%).
What are Wilson's Six Principles of Teratology?
1. Susceptibility depends on gentotype of conceptus.
2. Susceptibility varies w/ development stage.
3. Teratogenic agents act in specific ways on developing cells & tissues to cause abnormal development.
4. Final manifestations of deviant development are death, malformation, growth retardation, or functional deficit.
5. The access of adverse infulences to developing tissues depends on nature of agent.
6. Deviant development inc in frequency & degree as dosage inc
What is a major infectious agent that causes developmental abnormalities?
Rubella: The congenital Rubella Syndrome includes congenital heart dz, cataracts, deafness.
What are the only confirmed effects of ionizing radiation in humans?
Microcephaly and Mental Retardation
Which system is sensitive to teratogenic effects throughout fetal life?
The CNS
What radiation dosage elicits teratogenic effects?
25 rads
What is the most sensitive time for CNS damage from ionizing radiation?
8-15 weeks after LMP.
What is a category A drug?
Studies in women show that drug fails to demonstrate a risk to the fetus.
What is a category B drug?
1. Animal studies indicate no fetal risk and there are no human studies.
2. OR Animal studies indiate a risk that is not found in well controlled studies in pregnant women.
What is a category C drug?
1. There are no studies available in women or animals.
2. OR Drug maybe have teratogenic effects in animuls but no studies available in women.
What is a category D drug?
A positive risk of fetal effects exists, but benefits of using drug outwigh risk in some situations.
What is a category X drug?
There is definite fetal risk and risk clearly out weights any possible benefit.
What is Bendectin?
A product prescribed to ameliorate N/V in early pregnancy (approved by FDA), but was taken off market b/c of lawsuits that it caused birth defects.
Where is the most highly oxygenated blood in the fetus?
In the umbilical vein, which returns blood from the placenta to the fetus.
Can the umbilical venous pO2 ever be higher than uterine vein pO2?
No
Why does HbF have a higher O2 affinity than HbA?
HbA binds 2,3-DPG more avidly than HbF.
What are the 3 shunts of the fetal circulation?
1. Ductus Venosus
2. Foramen Ovale
3. Ductus Arteriosus
Do the fetal ventricles function in parallel or series?
Parallel
What is the fetal CO?
300 ml/min/kg -- 3x higher than that of the mother.
How long does it take to deplete the fetus of oxygen?
Two minutes after fetal O2 supply is cut off.