Chap 3 prenatal development Flashcards
identify prenatal development stages and discuss milestones in eac
chap 3 objective #1
Discuss common agents that cause defects in the developing embryo
chap 3 objective #2
- Gestational Age
- Trimester System
Prenatal classification system
- Measured in weeks
- From 1st day of last menstrual period
- From moment of conception (in vitro )
Gestational Age
- arguments against this method
- 40 weeks (or even 38) is not divisible by 3
- Not precise enough
- still use though
Trimester system
- Period of the Zygote
- Period of the Embryo
- Period of the Fetus
3 prenatal periods
- lasts approximately 2 weeks
- From time of conception to zygote implanted into the uterus
Zygote period
- extends to the end of 8 weeks past conception
- All major body structures formed
Embryo period
Extensive growth and refinement of body structures: “growth and finishing”
Fetus period
Most important prenatal period
Embryo period*
important per Dr W.
Trimester 1
Trimester 2
Trimester 3
Milestones of Prenatal development
- this is an organism containing 48
- chromosomes and typically not susceptible to teratogens
Zygote
- the zygote is implanted into the uterus
- teratogens can be harmful
Embryo
Embryo divides into 3 layers
- ectoderm
- Mesoderm
- Endoderm
nervous system in the skin
ectoderm
muscle, skeletal, circulatory, organs
Mesoderm
digestive (immunity) , lungs, urinary tracts
Endoderm
Weeks 3 through Week 8
period of the embryo
Ectoderm folds over to form the neural tube
*becomes the spinal cord and brain
Week 3
- Neural tube becomes thicker and begins to close, producing the spinal core
- limbs develop in a proximodistal fashion
Week 4
- placental circulation occurs via the umbilical cord
- continued differentiation of the brain (maturation)
- stomach and intestines continue to grow and change position
Week 5 and 6
- Ossification
- heart will have primitive arteries
- head is forming more and body is curled
Week 7 and 8
Weeks 9 through Weeks 32 or more
- Head continues to grow faster than body
- sex becomes visible
- Digestion system begin to function
- improved vascularization occurs
- heartbeat can be heard the stethoscope
- Body becomes more proportional
- coordination improves
- ossification stays active
- reflexes strengthen
Week 13 through 16
- feel movement
- adipose tissue and brown fat develops
- continued lung maturation
Week 17 through 20
this allows fetus to maintain body heat
Brown-fat
- increased survival rate
- increased weight gain
- enhanced lung development
- surfactant- develops
- by the end taste buds appear
- eyelids are completely formed and eyelids open
Week 21 through 25
what week can the fetuses be born and still survive with intensive life support
Week 23
Age of viability
22 to 26 weeks
- increased weight gain
- fat accumulation
- still has immature thermal regulation
- neonatal reflexes are fully developed
- head hair appears
Week 26 through 29
- continued weight gain
- still require thermal support if born between 30-32 weeks: survival chances much higher
week 30 though 34
- additional weight gain (up to 2lbs)
- Fetal movement may begin to decrease
Week 35 through 38
at birth
- Passageway between pulmonary trunk and aorta (allows for bypass of the lungs)
- typically closes spontaneously
Closure of ductus arteriosus
at birth
- passageway between the right and left atrium
- Closes within first 3 months
Closure of foramen ovale
