L4 (prenatal) Flashcards
Preformationism
ultimate nativist theory of development in which prenatal life starts with a fully-formed individual (either in the sperm or egg) that gets bigger
Canalization
developmental reduction in plasticity of cells (i.e. reduction in ability to change as we age)
Beginning of life according to Beng of West Africa
life begins when newborns choose not to return to afterlife (wrugbe) rather they are born as a reincarnation of an ancestor
you know they’ve chosen to stay when their umbilical stump drops off a couple weeks post-birth
Gametes
haploid sex cells (eggs and sperm)
Haploid cells
contain only half the genetic material found in other diploid cells (23 chromosomes instead of 23 pairs of chromosomes)
Eggs vs sperm
- much bigger (the largest cell) and formed prenatally
- smaller and formed throughout the lifespan
How many sperm fertilize eggs?
millions of sperm are ejaculated but only ~200 reach the egg (survival of the fittest)
Zona reaction
chemical reaction that blocks other sperm from entering an egg
takes around 6 hours for sperm to penetrate by 6-7 inches
What happens to sperm when it fertilizes an egg?
sperm tail falls off and the rest goes into the egg
Zygote
fertilized egg with 23 chromosomes from mom and 23 chromosomes from dad
3 principles of prenatal development
- cephalocaudal (head first)
- basic first then more specialized (e.g. arm bud, hand paddle, then fingers)
- important first (e.g. brain, heart)
4 processes that transform a zygote into an embryo then into a fetus
- cell division (mitosis) resulting in the proliferation of cells
- cell migration
- cell differentiation
- apoptosis
Cell migration
movement of cells from their point of origin to somewhere else in the embryo
Cell differentiation
embryo’s unspecialized stem cells are transformed into ~350 different types of cells
Apoptosis
selective death of certain cells that enables prenatal development
3 periods in prenatal development
germinal (conception to 2 weeks), embryonic (3rd to 8th week), fetal (9th week to birth)
Germinal period
lasts until the blastocyst is implanted in the uterine wall where rapid cell division takes place
after conception, zygote > blastomere > morula > blastocyst
When are twins determined?
germinal period
Monozygotic twins
identical, share the same genetic material, and result from the division of inner cell mass (usually share the same placenta)
Dizygotic twins
fraternal, share 50% of genetic material, and result from two different eggs getting fertilized by two different sperms
What happens to MZ twins when inner cell mass split happens in the first 2 days of the germinal period?
they get their own amniotic sacs and sometimes even their own placentas
What happens to MZ twins when the inner cell mass split happens late?
they may share the same amniotic sac and risk having umbilical cord entanglement; become conjoined if very late
Is twinning hereditary?
identical twinning is uncommon and random while fraternal twinning is hereditary (tendency for hyper-ovulation is passed down)
Embryonic period
following implantation, blastocyst becomes an embryo, placenta and amniotic sac form, and chemicals are released to preserve the pregnancy (e.g. progesterone)
Why is the embryonic period the most sensitive period of development?
- rapid cell division takes place and major organs begin to form
- when most miscarriages occur
Amniotic sac
- filled with amniotic fluid
- protects the baby and lets it move unhampered by gravity
Placenta
a semipermeable network of blood vessels that allow for the exchange of fluids between the fetus and their mom and produces hormones (e.g. estrogen, progesterone)
connected to the embryo by the umbilical cord
What happens in weeks 2-3 of prenatal development (from germinal to embryonic period)?
inner cell mass folds into 3 layers: top, middle, bottom
What does the top layer of the inner cell mass transform into?
nervous system (neural tube then brain and spinal cord), nails, teeth, inner ear, lens of eyes, outer surface of skin
spina bifida results from errors in neural tube closure so should take folic acid
What does the middle layer of the inner cell mass transform into?
muscles, bones, circulatory system, inner layers of skin, other intestinal organs
What does the bottom layer of the inner cell mass transform into?
digestive system, lungs, urinary tract, glands
When do most spontaneous abortions/miscarriages occur?
before 11 weeks of prenatal development (during embryonic period) wherein most embryos have severe defects like aneuploidy (having extra/missing chromosomes)
Androgens (e.g. testosterone)
produced by all fetuses but especially by genetically male fetuses, causing their testes to develop, which eventually produces testosterone itself
Outcome of testosterone in a genetic female
congenital adrenal hyperplasia (male anatomy and brain differentiation)
Outcome of lack of sensitivity to testosterone in a genetic male
androgen insensitivity syndrome (no male organs and often raised as a female)
At what age does gender identity emerge?
present from age 2 or 3 but both cisgender and transgender children reliably identify with their gender by age 5
How are males affected by x-linked recessive traits and y-linked traits?
- males (XY) are more susceptible x-linked recessive traits as they only need 1 gene (from their mother) to express the trait
- only males are affected by y-linked traits (from their father)
Examples:
* X-linked: hemophilia and fragile-x syndrome
* Y-linked: webbed toes
When does apoptosis begin on a large scale?
24 weeks
When do fetuses’ hair and neural cells tune to different sounds?
25 weeks
Fetal breathing
movement of the chest wall, pulling in and expelling small amounts of amniotic fluid help the respiratory system become functional
What are some signs that fetuses are practicing for life outside the womb?
- bringing their hand to their mouth
- fetal breathing
- swallowing of amniotic fluid
- cells in visual pathway engage in spontaneous activity
How does fetal swallowing aid in their development?
swallowing of amniotic fluid promotes the development of the palate and aids in the maturation of the digestive system
What is the relationship between activity differences before and after birth?
individual differences in activity level continue after birth (more active fetuses = more active children)
When does fetal movement begin?
5-6 weeks (jerky and uncontrolled movement) and at 7 weeks, fetuses hiccup!
all during embryonic period
Which time of day are fetuses most active (in terms of movement)?
early morning and late evening
How is fetal movement related to cortical inhibition?
in the second half of pregnancy, only 10-30% of movement is thought to be related to cortical inhibition
GABA selectively attenuates activity of other neurons in the cortex
When do fetuses engage in rest during pregnancy?
- rest/activity cycles every few minutes at 10 weeks
- sleep around 75% of the time toward the end of pregnancy
How do fetuses experience senses of touch, taste, smell, and hearing?
- feel their own movements
- taste and smell amniotic fluid
- hear their mother’s voice and bodily sounds
- seeing is minimal (although eye mainly develops prenatally)
When do fetuses habituate to speech sounds and dishabituate to new sounds?
32 weeks
What are the preferences of full-term new borns?
- mother’s voice and smell
- food, music, words, stories they’ve experienced prenatally
Teratogens
any environmental agent that can potentially cause harm during prenatal development
Factors that influence the effect of teratogens
- timing
- individual differences in the fetus
- has a dose-response relation (cumulative impact)
Thalidomide poisoning
a teratogen that turns offs genes that regulate proteins that develop limbs
only takes effect prior to limb development
Examples of teratogens
excessive alcohol intake early on, smoking, mercury, marijuana, illegal drugs, maternal diseases (e.g. flu)
though sleeper effects may make them difficult to detect
Facial features of people with fetal alcohol syndrome
elfin ears, eye folds, large flat upper dentate, thin lips, small and widely spaced eyes
3 maternal factors in prenatal development
- age (young and old parents put baby at risk)
- nutrition (e.g. folic acid and sufficient calories is important)
- stress-level (high stress impacts hormone environment in womb)
What are the negative effects of pre- and post-natal depression and anxiety (of mother) on child development?
- deficits in attention and cognitive control
- more impulsivity
- reduction in fetal brain connectivity
Potential risks of administering SSRIs to mothers during pregnancy
cardiac issues and withdrawal symptoms at birth, but NOT autism
confound in link between SSRIs and autism
