Prenatal development (ch 4) Flashcards
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
Fetal - Week 33-38:
- Last 6 weeks of full term pregnancy bring further weight gain and brain activity
- Lungs mature and begin to expand and contract
Teratogens:
Any disease, drug, or environmental agent that can harm a developing organism
- effects = worse during critical period
Newborns routinely screened with Apgar test, which is quick assessment of:
- Heart rate
- Respiration
- Color
- Muscle tone
- Reflexes
leading cause of infant mortality
prematurity
Low birth weight
- weighing less than 5.5 pounds (or 2500 grams)
- Extremely LBW weigh less than 2-3 lbs (or 1000 grams)
- Micropreemies weigh less than 1.75 lbs (or 800 grams)
- Less than 1 percent of births but comprise 36 percent of hospital costs
LBW associated with…
- lower SES
- African-American ethnicity
- smoking, stress
- multiple births
Werner’s 40 year longitudinal study revealed:
- Effects of prenatal and perinatal complications decrease over time
- Outcomes of early risk depend on quality of postnatal environment
- Protective factors - Personal resources: intelligence, sociability, communication that help them choose or create more nurturing or stimulating environments
Considered infertile after
one year of trying to get pregnant
Effect of alcohol during 1st trimester
Facial abnormalities
Effect of alcohol during 2nd and 3rd trimester
Growth and brain development = stunted
