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
