week 1 embryonic development - fertilization -> morula -> trophectoderm ( -> chorion and placenta) +
ICM (-> embryo proper)
3 key events in week 1+2 of development - - implantation
- gastrulation
- axis and layer formation
*errors in first 2 weeks are lethal*
implantation - - blastocyst adheres to endometrium
- initiates placenta formation
- occurs 6-8 days after fertilization (MUST occur within 10 days
gastrulation - gut tissue moves inside embryo
axis formation - orientation determined by sperm entry point
- head-tail (rostrocaudal)
- stomach to spine (dorsal-ventral)
- left-right (sagittal plane)
,miscarriage rates - 10-20% of known pregnancies
30-50% of all pregnancies
weeks 2-8 of development - - morphogenesis and organogenesis
- starts to look like a human (head, limb buds)
- all organ systems established (circulatory system becomes essential)
** errors result in severe abnormality or lethality
fetal development - - all major organs present BUT not all functional (gut and longs dont work)
- grows from 1 inch to 20+ inches
- critical period for CNS development
preterm - <37 weeks
- increased risk of mortality because of undeveloped CNS and respiratory system
- 25% survive @ 6 months
fetal surgery - - performed between 18-30 weeks
- used to correct severe spina bifida
- usually hysterotomy (fetus removed for surgery)
critical vs sensitive periods - critical = error is major or fatal
- lays the foundation for further development
- embryo as a whole and each organ system/structure have a critical period
sensitive = error is problematic but not fatal
dysmorphology - study of human congenital malformations (birth defects)
- not usually preventable
- diagnosed using 'normal' standards
, - ~3% of infants have major anomaly
- ~ 5-10% have minor anomaly
major vs minor anomalies/malformations - major = require medical attention
minor = don't require medical attention BUT may indicate more serious defects present/ help identify
syndromes i.e., marfan
4 dysmorphology classifications - - malformations
- disruptions
- deformations
- dysplasia
malformations - defects of organs that result from intrinsically abnormal development
- incomplete, redundant, or aberrant development
- isolated or syndromic
i.e., split hand
disruptions - defects resulting from interference with originally normal developmental processes
- not usually genetic
i.e., teratogenic influences
deformations - abnormal shape/form of body part resulting from mechanical factors/force
i.e., club foot
dysplasia - abnormal organization of cells into tissues
- usually not confined to single organ
i.e., CT in Marfan's, bone in achondroplasia
3 patterns of dysmorphology - - sequences
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