Prenatal development (ch 4) Flashcards
(34 cards)
Germinal Period
First stage of prenatal dev.
- lasts approximately two weeks –
- zygote divides through mitosis and forms blastocyst that implants into blood vessels of uterine wall
- Only half of fertilized ova implant successfully
- 15-20 percent recognized pregnancies miscarry
- 50 percent of unrecognized pregnancies miscarry
Day 1 of Germinal period
Fertilization usually occurs within 24 hours of ovulation
Day 2 of Germinal period
The single-celled zygote begins to divide 24-36 hours after fertilization
Day 3-4 of Germinal period
- The mass has 16 cells – called morula
- Travelling down fallopian tube to the uterus
Day 5 of Germinal period
- Inner cell mass forms – entire mass called Blastocyst
- Size of pinhead
Day 6-7 of Germinal period
Blastocyst attaches to the wall of the uterus
Day 8-14 of Germinal period
Blastocyst becomes fully embedded in the wall of the uterus
- Now have approximately 250 cells
Embryonic period
- week 3-8
- Organogenesis - formation of every major organ
- Layers of blastocyst differentiate forming structures that sustain development
- Sexual differentiation
Events of embryonic period - Wk 3
- Embryo 1/10 of an inch
- Become elongated
- Three layers emerge: ectoderm, mesoderm, and endoderm
Embryonic period Week 4:
- Embryo so curved that the two ends almost touch
- Outer layer (ectoderm) folds into the neural tube
- From mesoderm, a tiny heart forms and begins to beat
- Endoderm differentiates into gastrointestinal tract and lungs
- 21-28 days: eyes develop
Embryonic period: week 5
- Ears, mouth, throat take shape
- Arm and leg buds appear
- Handplate from which fingers will emerge appears
- Heart divides into two regions
- Brain differentiates into forebrain, midbrain, and hindbrain
Embryonic - Week 6-7
- Embryo almost 1 inch long
- Heart divides into four chambers
- Fingers emerge from handplate
- Primative facial features evident
- Sexual differentiation begins
Embryonic - Week 8
- Most structures and organs present
- Ovaries and testies are evident
- Embryo begins to straighten and assumes more human appearance
Neural tube defects occur during which period
- during embryonic period – 25-29 days after conception
- 1 in 1000 pregnancies – neural tube fails to close completely
Spina bifida:
- Neural tube defect
- part of the spinal cord not fully encased in the protective covering of the spinal cord
Anencephaly:
- Neural tube defect
- top of neural tube does not close and main portion of brain above brain stem does not develop
- Most common when mother is deficient in folic acid
Fetal period
- 9 weeks to birth
- Cells proliferate, migrate, and differentiate
- Differentiation of cells occurs according to where cells migrate
- Organ systems continue to grow and begin to function
- Sex organs appear during 3rd month of pregnancy
- When survival is possible if brain and respiratory system are sufficiently developed
- Weight gain
- Organized and adaptive behaviors develop
- Patterns of heart rate, activity level
Age of viability reached at about
23 weeks
Fetal period: Week 9
- Bone tissue emerges and embryo becomes a fetus
- Head of the fetus looks huge compared to the rest of the body – takes up about ½ length of fetus
- Fetus can open and close its mouth and turn its head
Fetal - Week 10-12
Fingers and toes are clearly formed
- External genitalia developed
- Movements increased substantially
- Arms and legs kick vigorously but fetus still too small for mother to feel movement
- Fetus also shows breathing movements with its chest
- Some reflexes
Fetal - Week 13-16:
- Heartbeat should be audible with stethoscope
- Fetal movements may become apparent to mothy
- Fetus 4.5 inches long
- Skeleton becomes harder
Fetal - Week 17-22:
- Fingernails and toenails, hair, teeth buds, and eyelashes grow
- Brain development is phenomenal and brainwaves detectable
Fetal - Week 23-25:
- Age of viability – fetus has change of surviving outside the womb
- 12 inches long, 1 pound
Fetal - Week 26-32:
- Fetus gains weight and its brain grows
- Nervous system becomes better organized
