Epigenesis
The emergence of new structures and functions during development
Canalization
- Refers to developmental
reduction in plasticity - Initially cells can become
anything (stem cells); as
development progresses, it’s
harder to change paths - Studies with frogs: you can
change a cell’s path by simply
moving it - development
influenced by neighbouring cells
Gametes
Egg and sperm
- Eggs are much bigger (largest cell!) and all formed
prenatally; sperm much smaller and formed throughout
lifespan - haploid = only half the genetic material found in other
diploid cells - 23 chromosomes v. 23 pairs of chromosomes
Fertilization & Conception
- While millions of sperm are ejaculated, only ~200
reach the egg (most get lost, tangled up, or have
other genetic defects - survival of the fittest!) - Takes about 6 hours to go 6-7 inches
- When one penetrates, zona reaction occurs,
blocks other sperm from entering - sperm tail falls off and rest goes into egg
- zygote = fertilized egg with (hopefully) 23
chromosomes from mom and 23 from dad
Sex differences do not begin at conception
Conception rates are equal, but girls more likely to miscarry early
Sexual Differentiation
- All about hormones
- Androgens, including testosterone, are produced
by the genetically male fetus and cause male anatomy
to develop that eventually produces testosterone
itself - Testosterone in a genetic female can cause male
anatomy and brain differentiation - Studies have shown a link between levels of prenatal
testosterone and gender-typed behaviour and
homosexuality - Not uncontroversial, more (bigger) studies needed
Processes of Development
Four major developmental processes transform a zygote into an
embryo and then into a fetus:
1. Cell division = mitosis results in the proliferation of cells
2. Cell migration the movement of cells from their point of origin to
somewhere else in the embryo
3. Cell differentiation transforms the embryo’s unspecialized stem cells
into roughly 350 different types of cells
4. The selective death of certain cells, or apoptosis, also enables prenatal
development
* hand development
Germinal & Embryonic Periods
Germinal (Conception - 2 weeks):
- Begins with conception and lasts until the zygote becomes implanted in the uterine wall
- Rapid cell division takes place
Embryonic (3rd - 8th week):
- Following implantation, major development occurs in all the organs and systems of the body
- Blastocyst implants into uterine wall - now an embryo
- Placenta and amniotic sac form, chemicals released to preserve pregnancy
- Most sensitive period of development
- Rapid cell division
- Major organs forming
- Most miscarriages happen here
Fetal (9th week - birth):
- Continued development of physical structures and rapid growth of the body.
- Increasing levels of behavior, sensory experience , and learning
Twins
- Determined during Germinal Period
Monozygotic = Identical; inner cell mass splits
- Siblings share 100% genetic material (not exactly)
- Identical - usually share same placenta (wit own amniotic sacs)
- It doesn’t always happen, if split happens late, may share same sac - risk of umbilical cord entanglement
- very late - conjoined
- Identical twinning is not hereditary, while fraternal/DZ twinning is ( tendency for hyper-ovulation can be passed down)
Dizygotic = fraternal; 2 eggs released and fertilized by different sperm
- Siblings share 50% genetic material
Embryo
In week 2-3, inner cell mass folds into 3 layers
- top = nervous system, nails, teeth, inner ear, lens of eyes, outer
surface of skin
- middle = muscles, bones, circulatory system, inner layers of skin,
other intestinal organs
- bottom = digestion, lungs, urinary tract, glands
Top layers folds in on itself and becomes the
neural tube
- becomes the brain and the spinal cord
Spina bifida results from closure errors here
Amniotic Sac/Placenta
- Amniotic sac filled with amniotic fluid - protects baby, lets it move unhampered by gravity
Placenta
- a network of blood vessels that allows for exchanging fluids between fetus and mom
- Connected to embryo by the umbilical cord
- Semipermeable - let good stuff in and bad stuff out (also let bad stuff in)
- Produces hormones
Fetal Activities
Movement
- Babies move from 5-6 weeks!
- 7-week-old fetuses hiccup
- Activity level individual differences, and there’s continuity in
this after birth
- More active fetuses = more active, less inhibited children
Seem to “practice” for life outside the womb:
- Bringing hand to mouth
- Swallowing amniotic fluid promotes the normal development of the palate and aids in the maturation of the digestive system
- Movement of the chest wall and pulling in and expelling small amounts of amniotic fluid help the respiratory system become functional
Sleeping
Quiet Sleep
- Occasional startle
- No eye movements
- Stable heart rate
Active Sleep
- Like REM
- Frequent body and eye movements
- Heart rate accelerates in association with movements
- Most common state
Quiet Awake
- No body movements
- Eye movements
- Stable heart rate
- Rare
Active Awake
- Continual body and eye movements
- Unstable heart rate
- Tachycardia (increased pulse rate)
Fetal Senses
Fetus feels, tastes, smells, and hears
- Feels own movements
- Tastes and smells amniotic fluid (sweet = good)
- Hear mom’s bodily sounds; her voice; startles to loud sounds
- Seeing is minimal
Fetal Learning
Full-term newborns prefer things they experienced and heard prenatally
Hazards to Prenatal Development
Miscarriage = spontaneous abortion
Premature Infants
- Anything under 34 weeks gestation is considered premature
- Incidence of lifelong problems increases with premises
Teratogens
Any environmental agent that can potentially cause harm during prenatal development
Identifying Teratogens
- Alcohol
- Smoking
- Mercury
- Marijuana
- Maternal diseases
- Illegal drugs
Maternal Factors
- Age
- Nutrition
- Stress-level
Birth
- Birth not painful for baby
- Large cultural differences in childbirth practices
- Pain relieving drugs do not harm newborns nor increase C-sections
- Development is continuous
Newborn
- Lots of Sleep
- About half REM
- Autostimulation theory - brain activity during REM facilitates visual development in fetuses and newborns
- Myoclonic twitching - jerky movements; building sensorimotor maps
- Can learn while sleeping
Neonatal Intensive Care
Babies in the NICU for a variety of reasons:
- Prematury-related issues: immature lungs mean can’t breathe on own; jaundice
- Developmental defects that are corrected post-birth; recovery from surgery in NICU
Effects on Infants
- Noise - beeping machines
- Light - 24 hours/day
- Pain - pin pricks, surgical cuts
- Drugs - analgesics, antibiotics, sedatives
- Separation from maternal interaction
Effects on Parents
- Parents have little or no preparation for NICU experience
- Depending on level of prematurity, less prepared for the arrival of (even a healthy) infant
- Feelings of fear, grief loss of control
- Life or death decisions
Outcomes for NICU infants
- Some infants more sensitive to pain (often premature)
- Some infants less sensitive (often term, but ELBW)
- Pain tolerance issues appear to diminish over time
Post-NICU premature/ELBW babies
- Regardless of effects of NICU, it is simply harder to interact with a preterm/LBW infant
- Show less attention to novel stimuli, issues habituating
- Self-regulation issues - difficult to settle, irritable
- Sleep issues
- Mixed cues in mother-infant facial exchanges
Multiple-Risk Model
Long term outcomes depend on whether had one or more than one risk factor
