Pre- and Postnatal Development Flashcards
Conception
CONCEPTION
humans originate as a single cell resulting from the union of two highly specialised cells - the sperm and egg. these gametes (germ cells) are unique and are produced through meiosis, a special type of cell division in which the eggs and sperm receive only one member from each of the 23 chromosome pairs contained in all other cells of the body. this reduction to 23 chromosome pairs in each gamete is necessary for reproduction as the union of egg and sperm must have the normal amount of genetic material (23 chromosomes).
process of reproduction starts with launching an egg from one of the woman’s ovaries into the adjoining fallopian tube. the egg moves through the tube towards the uterus while it emits a chemical substance that attracts sperm towards it. if sexual intercourse takes place near the time the egg is released, conception, the union between sperm and egg is possible. every ejaculation has 500 million sperm pumping into the woman’s vagina with a head full of the genetic material and tail used to propel the sperm through the woman reproductive system.
to initiate conception, a sperm must travel for around 6hrs (of the 500 million sperm, only 200 get near the egg). many causes for high failure rate (by chance or have serious genetic or other defects), therefore the sperm that get near to the egg are likely to be healthy and structurally sound (Darwinian type - “survival of the fittest”).
when one sperms head penetrates the egg, a chemical reaction seals the membrane, preventing other sperm from entering. the tail of the sperm falls off, the contents of its head gush into the egg, and the nuclei of the two cells merge within hours. the fertilised egg, known as the zygote, now has a full complement of human genetic material, 23 chromosomes from the mother and the same for the father. prenatal development has now begun.
4 Major Developmental Processes
4 Major Developmental Processes that underlie the transformation of a zygote into an embryo and then a fetus.
the first process is cell division (mitosis), where the zygote divides rapidly over the course of 38 weeks, the barely visible zygote becomes a newborn of trillions of cells.
the second process is cell migration, the movement of newly formed cells away from their point of origin. among the many cells that migrate are the neurons that originate deep inside the embryonic brain and then, like pioneers settling new territory, travel to the outer reaches of the developing brain.
the third process is cell differentiation, the embryonic stem cells specialise in structure and function, they develop roughly 350 different types of cells, which perform particular functions on behalf of the organism. this process of differentiation is one of the major mysteries of prenatal development. the initial flexibility and subsequent inflexibility of cells, as well as the importance of location are crucial factors in determining which type of cell a given stem cell will become.
the fourth process is death, involves the selective death of certain cells. the role of the genetically programmed “cell suicide” called apoptosis, is readily apparent in hand development: the formation fo fingers depends on the death of cells in between the ridges in the hand plate (death is reprogrammed for the cells that disappear from the hand plate).
in addition to these four developmental processes, we need to call attention to the influence of hormones on prenatal development. for example, hormones play a crucial role in sexual differentiation. the absence or presence of androgens, a class of hormones that includes testosterone, causes development to proceed one way or the other. if androgens are present, the male sex organs develop. one of many ways the fetus influences its own development.
Early Development
travelling through the fallopian tube to the womb, the zygote doubles its number of cells roughly twice a day. by the 4th day after conception, the cells arrange themselves into a hollow sphere with a bulge of cells, called the inner cell mass, on one side.
Identical twins result when a splitting in of the inner cell mass, thus both have exactly the same genetic makeup. Fraternal twins result when two eggs are released and both fertilised.
At the end of the 1st week, implantation occurs in which the zygotes embeds itself in the uterine lining and becomes dependent on the mother for sustenance. well before the 2nd week, it will be completely imbedded within the uterine wall.
after implantation is when the embedded ball of cells start to differentiate. once the inner cell mass becomes the embryo, the rest of the cells become the amniotic sac (transparent, fluid-filled membrane that surrounds and protects the fetus) and placenta (a support organ for the fetus) that enables the embryo to develop (two key support systems).
The amniotic sac acts as a protective buffer for the developing child, providing the right temperature and cushioning. the placenta is a network of blood vessels extending into the tissues of the uterus, with a total surface area of about 10 square yards. Blood vessels running from the placenta to the embryo and back again are contained in the umbilical cord.
The inner cell mass fold itself into three layers during the 2nd week, each with a different developmental destiny. after this, a U-shaped groove forms down the center of the top layer. the folds at the top of the groove move together and fuse, creating the neural tube. one end of the tube will swell and develop into the brain, the rest will become the spinal cord.
the placenta prevents the blood systems of the mother and fetus from mixing. However, the placental membrane is semipermeable, meaning that some elements can pass through it. Oxygen, nutrients, minerals and some antibodies are transported to placenta through the mothers blood system and cross the placenta to enter the fetal blood system.
the placenta also is a defensive barrier against a host of dangerous toxins and infectious agents that can inhabit the mothers body and could be harmful or even fatal to the fetus.
the placenta also is the production of hormones, including estrogen, which increases the flow of maternal blood to the uterus, and progesterone, which suppresses uterine contractions that could lead to premature birth.
Fetal Behaviour
Movement:
from 5 to 6 weeks after conception, the fetus moves spontaneously (starting with bending head and spine).
from 7 weeks hiccups can occur.
Swallowing is also an important fetal movement, swallowing amniotic fluid, which passes through its gastrointestinal system. most of the fluid is extracted back into the sac. one benefit of this activity is that the tongue movements promote the normal development of the palate. another benefit is that it helps the digestive system to mature properly. therefore swallowing amniotic fluid prepares the fetus for survival outside the womb.
the fetus also moves its limbs, and by 12 weeks most of the movements that will be present at birth have appeared (mother still unaware of them). prenatal continuity (constant activity of fetus) extends into the postnatal period, at least for boys. fetuses that are more active during gestation exhibit temperaments during infancy that suggest greater levels of emotion regulation.
another fetal movement it the fact at birth the newborn must start breathing. for that to happen, the lungs and the rest of the respiratory system must be mature and functional. to achieve this, 10 weeks after conception, the fetus exercises their lungs by “fetal breathing”, which involves an ongoing and consistent pattern of lung activity, fetal breathing is initially infrequent and irregular.
Behavioural Cycles:
rest-activity-cycles are bursts of high activity alternating with little or no activity for a few minutes at a time at 10 weeks old and become very stable during the second half of pregnancy.
longer-term patterns, including daily (circadian) rhythms, also become apparent, with less activity in the early morning and more activity at night. the confirms the impressions of most pregnant women that their fetuses wake up and start doing acrobatics just as they themselves are trying to go to sleep.
near the end of pregnancy, the fetus spends more than 3/4ths of its time in quiet and active sleep states like those of the newborn. the active sleep state is characterised by REM, just as it is in infants and adults.
Fetal Experience and Learning
EXPERIENCE
Sight and Touch:
visual experience is minimal, however does experience stimulation from its own activity (moving around, touching themselves (umbilical cord, face, sucking thumb)). by full term, fetuses respond to maternal movements suggesting that their vestibular systems - the sensory apparatus in the inner ear that provides information about movement and balance - also functioning before birth.
Taste:
amniotic fluid contains a variety of flavours. the fetus can detect these flavours, and likes some better than others (has a sweet tooth). Taste sensitivity and flavour preferences exist before birth.
Smell:
amniotic fluid takes on odours from what the mother has eaten. during birth, they can smell scents like curry and coffee in the amniotic fluid who has recently consumed them. smells can be transmitted through the liquid, and amniotic fluid comes into contact with the fetus’s odor receptors through fetal breathing, provides the fetus with opportunities for olfactory experience.
Hearing:
the womb is filled with noise (ranges from 70-95 decibels) including maternal sounds including the mothers heartbeat, blood pumping, her breathing, swallowing, and rude noises made by digestive system. the most prominent and frequent is the mothers voice (gentle rhythm and pitch patterns).
LEARNING
the fetus learns from many of its experiences in the last 3 months of pregnancy, after the central nervous system is adequantly developed to support learning. scientists can examine sensory experiences by the fetus is through using habituation.
*Habituation: a form of learning that involves a decrease in response to repeated or continued stimulation; can be observed prenatally ~30 weeks.
Habituation is a critical sign of learning, the body has learned that the stimulus is provided repeatedly (becomes boring), remembering that the fetus has heard or felt the stimulus before. as soon as a new stimulus is provided the body knows that this is a new stimulus and becomes interested again, a process known as dishabituation.
if fetuses can learn and remember something about their mothers voice prenatally, this could also provide them with a running start for learning about other aspects of speech after birth.
Learning can persist after birth (Partanen et al., 2013, PNAS). the study shows that prenatal experiences have long lasting effects. Moms played CD 5-7 times/week from week 29 till birth. Three variants of pseudowords (interspersed with music):
[tatata] frequent, standard
[tatota] infrequent vovel change
[tatata] infrequent pitch change- rare in Finnish
EEG measurement after birth
- the specific flavours the mother digests has an influence on what the baby prefers at birth for scent.
- experiences in the womb can lead to long-lasting taste preferences.
- newborns can remember sounds they heard in the womb and have auditory preferences
Name periods of prenatal development
Prenatal Development
Is the process in which a baby develops inside the mothers womb. It usually takes around 38 weeks to complete, and during this time a single cell becomes a full term baby.
the entire period is divided into 3 primary stages of prenatal development:
- Germinal Period - zygote implanted in uterine wall
- Embroynic Period - cell division, migration, differentiation, death embryonic stem cells are initially equivalent and interchangeable
- Fetal Period - growth of physical structures and body
Each of these stages is important for reaching the ultimate goal of a healthy baby.
Germinal Period:
conception is the beginning of the germinal period, the stage occurs during the first 2 weeks of development. It ends when the zygote (the union of the sperm and egg into a single cell) is implanted in the uterine wall.
The zygote moves along the fallopian tube towards the uterus, at the same time it rapidly divides in the process called cleavage. Once it reaches the uterus wall the zygote becomes what is called blastocyst and begins to implant into the wall of the uterus. The germinal period ends when the blastocyst is fully implanted in the uterine tissue.
Embryonic Period:
This period lasts from 3rd week to 8th week. the blastocyst that planted into the uterus continues to divide rapidly, this process is called differentiation. The cells begin to take on different functions in the process of differentiation. one of them is the division between the cells that will make up the placenta, and the cells that will make the baby.
After this, a process called Gastrulation forms three layers called germ layers, the outer layer is called ectoderm, the middle layer is mesoderm and the endoderm is the deepest layer. Each layer will differentiate into different structures.
The ectoderm will form mainly outer tissues such as skin and hair as well as most of the nervous system tissues including the brain.
The mesoderm will form tissues inside the body such as the lungs, bones, and muscles including the heart. The endoderm will form tissues for the digestive track and the bladder as well as other internal organs.
All of the essential structures will have been formed both inside and outside by the time the embryonic period comes to an end. the new title of fetus is now given to the embryo.
Fetal Period:
the brain is very much in place at this point. the shape of it would be very similar when the baby is fully grown. the key development of the central nervous system is the formation of the specialised fold of ectodermal tissu, this is called the neural tube. the development of the brain structure really starts with the neural tube which is made of three parts, the forebrain, midbrain and hindbrain (embryonic brain regions). the neural tube nears completion by 3 to 4 weeks of castation, is the basis for all nervous development.
Forebrain - develops into the cerebral cortex which translates sensory stimulation. it also controls complex behaviours, thoughts, memories and problem solving.
Midbrain - develops into a neural relay station for sending information from the body to various sites of the brain.
Hindbrain - controls the most basic physiological processes such as breathing and heart rate
Spinal Cord - the path way for conveying info between the brain and the rest of the body
Hazards to prenatal development
- Teratogen from the environment: drugs, alcohol, pollutants
- Maternal Factors: age, nutrition, disease, emotional state
the most common fate of a fertilised egg is spontaneous abortion (miscarriage).
TERATOGENS
the crucial factor in the severity of the effects of the potential teratogens is timing. many teratogens cause damage only if they are present during the sensitive period (3rd to 8th week) in prenatal development. the major organs are the most vulnerable to damage at the time when their basic structures are being formed. because the timing is different for each system, the sensitive periods are different for each system.
In the 1960s Thalidomide was prescribed to treat morning sickness among other thinsa as well. However, those who took this medication between the 4th and 6th week after conception gave birth to babies with major limb deformities.
Another crucial factor is the amount and duration of exposure. most teratogens show a dose-response relation ( the greater the fetus’s exposure to a potential teratogen, the more likely it is that fetus will suffer damage and the more severe any damage is likely to be).
Although fetal programming can occur (negative effects of prenatal experience not being immediately evident). this because experiences during the prenatal period “program the physiological set points that will govern physiology in adulthood”.
the effects of teratogens can also vary according to individual differences in genetic susceptibility. thus, a substance that is harmless to most people may trigger problems in a minority of individuals whose genes predispose them to be affected by it.
finally, identifying teratogens is further complicated by the existence of sleeper effects, in which the impact of a given agent may not be apparent for many years.
Drugs:
- antidepressants
- Opioids
- Illegal drugs
- Cigarette smoking
- Alcohol
MATERNAL FACTORS
Age:
age is related to the outcome of pregnancy. older women as well as teenagers are at greater risk for many negative outcomes for themselves and their fetus. teenagers are more at risk of dying, whereas for older women they could experience fetal abnormalities (autism) and birth complications.
Nutrition:
inadequate diet from mother leads to nutritionally deprived unborn child. this can lead to neural tube defect such as spina bifida, smaller brain.
Disease:
rubella can cause malformations, deafness, blindness, and intellectual disabilities. STD’s such as herpes can damage the fetuses nervous system and cause a variety of serious defects such as hearing loss, blindness and even death. maternal flu and other types of infections may interact with genetic factors to lead to mental illness. The Zike virus, a mosquito-borne infection can cause a serious birth defect called microcephaly (baby head is much smaller than expected). this can causes problems with brain development.
Maternal Emotional State:
maternal stress (psychosocial stress/biological stress reactivity(how the maternal body reacts to the stress)) has a direct impact on the maternal-placental-fetal (MPF) stress biology. prenatal stress exposure affects the fetuses brain development and there is a higher susceptibility for diseases (body compostition/metabolic function).
high stress in mother during pregnancy can lead to behaviour problems in their children at 4 years of age.
mother can influence babies stress and vice versa before birth.
Moderators in this process that can make the maternal stress worse or better:
- biophysical and obstetric conditions (e.g. pre-prgnancy BMI, gestational weight gain, gestational diabetes, preeclampsia)
- biobehavioural factors ( e.g. diet, physical activity, smoking, sleep)
- stress-buffering factors (e.g. social support)
- child diet and nutrition
- child home environment
- parental stress
- maternal sensitivity, maternal-child attachment.
•Effects depend on sensitive period (particularly in embryonic weeks) and dose-response relation •Postnatal intervention (e.g. secure parent-infant bond, enriched environment) can sometimes buffer negative consequences of prenatal hazards
embryo genisis is a term used to describe all of the process of embryo development until the time it becomes a fetus. What we also see is that death happens in this process, so with the differentiation happening some cells will die. for example, when the fingers develop it is important that this process of dying happens otherwise the baby won’t just have 5 fingers. from a developmental point of view, organs do go through developing these phases. Other ones beginning to be susceptible to environmental factors, for example hazards.
the main organs that may be affected by environmental factors are heart, CNS, eyes, arms, legs, ears, brain, teeth, palate, and external genitalia.
A hazard could be environmental pollutants. this is why the embryo period is so critical
in the fetal period, birth defects such as spina bifida arise from abnormalities in the neural tube formation. from 4 to 12 weeks the neural tube develops differentiates into what will become various components of the neural nervous system.
Diversity of Childbirth Practices
research on the birth process has revealed that many aspects of the experience of being born, including squeezing in the birth canal, have adaptive value and increase the likelihood of survival for the newborn. although, cultural groups differ in their beliefs and practices related to childbirth, these differences are decreasing as expectant mothers gain access to more diverse birthing options.
child practices vary enormously.
all cultures pursue goals of safeguarding the survival and health of both the mother and baby, and ensuring social integration of the new person.
groups differ on the importance they give to these goals. expectant mother from south pacific island of Bali wants every relative to be present and has probably witnessed the birth process, whereas in the United States an expected mother has not experienced this and withdraws almost totally from her everyday life, with a small group of people at the birth and has a 32% chance of having a surgical delivery by cesarean.
Balinese approach to childbirth - emphasis on immediately socialising the infant.
vs.
Western groups - emphasis the physical health of both mother and child above all other concerns.
United states - home births remain riskier than hospital.
vs.
Ontario, Canada - home births are equal to hospitals (home births are more of a standard practice).
US has changed to some degree such as the social dimensions of birth, and the use of a doulas, using moderate delivery drugs and parents attending childbirth education classes to improve new born survival rates.
The Newborn Infant
Sleep
state - a continuum of arousal, ranging from deep sleep to intense activity (crying). your state dramatically affects your interaction with the environment; with what you notice, do, learn and think about.
Average newborn states in a 24hr day: quiet sleep - 8hrs active sleep - 8hrs drowsing - 1hr alert awake - 2.5hrs active awake - 2.5hrs crying - 2hrs
newborns sleep twice as much as young adults do. total sleep time declines regularly during childhood and continues to decrease, although more slowly, throughout life.
the pattern of two different sleep states Rapid Eye Movement (REM) sleep and non-REM sleep. REM sleep is an active sleep state associated with dreaming in adults; characterised by quick, jerky eye movements under closed lids, a distinctive pattern of brain activity, body movements, and irregular heart rate and breathing.
Non-REM sleep, in contrast, is a quiet sleep state characterised by the absence of motor activity or eye movements and more regular, slow brain waves, breathing, and heart rate. REM sleep constitutes fully 50% of a newborns total sleep time, and declines rapidly to 20% by 3 or 4yrs old and remains low for the rest of life.
why infants spend much time in REM sleep:
- helps to develop the infants visual system
- natural jerking movements (called myoclonic twitching) gives infants opportunities to build sensorimotor maps.
- learning while sleeping as their brains do not become disconnected from external stimulation to the same extent that the brains of older individuals do.
another difference between baby and older individuals is in sleep-wake cycles. newborns cycle between sleep and waking states several times in a 24hr period. infants sleep patterns come to match adults through cultural practices and pressures, such as bedtime rituals.
sleep techniques have been proposed to help parents and infants struggling to sleep; operant conditioning.
The Newborn Infant
Crying
evolutionary view:
adults strong reactions to infants crying could have adaptable value. infants cry due to illness, pain and hunger, which require the attention of caregivers. mothers are especially attuned to their infants cries as they possess behavioural predispositions. however mothers tend to spend more time with their infants than fathers, therefore cry recognition appears to be part of the learning process for all caregivers.
crying starts to decrease once the infant has somewhat more control over the environment.
soothing techniques:
swaddling - involves wrapping baby in cloths or a blanket, therefor restricting limb movement which provides a constant high level of tactile stimulation and warmth
distracting upset infant with interesting objects - but distress often resumes as soon as the stimulus is removed.
touch - carrying them, pats, rubs and strokes leads to less crying and smiling/vocalising more. decreases in heart rate, physical movement, and crying when carried by their mother.
response to distress:
Bell and Ainsworth (1972) found that prompt responding to infant cries predicted less crying several months later. Yet, Hubbard & van IJzendoorn (1991) found that infants whose cries were ignored during the first 9wks cried less during the next 9wks. Both perspectives are valid.
Colic:
even aftering trying to soothe them, some infants are prone to excessive, inconsolable crying for no apparent reason during the first few months of life, a condition called colic. they also have high-pitched, unpleasant cries. causes of colic are unknown and may include allergic responses to their mothers diet ingested via breast milk. not a rare condition, ends around 3mnths of age and leaves no ill effects. seeking social support is key to provide relief from stress, frustration and sense of inadequacy and incompetence they may feel.
Negative Outcomes at Birth
Infant Mortality
death during the 1st year after birth is now relatively rare in the industrialised world, thanks to improvements of public health and general economic levels.
in the US, in 2015 the infant mortality rate was 5.87 deaths per 1000 live births, the lowest in US history but still high compared to other industrialised nations.
why is it so high? poverty - many low-income expectant mothers have no health insurance and thus limited access to good medical and prenatal care
Negative Outcomes at Birth
Low Birth Weight
US - average weight - 7 1/2 pounds
those under 5 1/2 pounds are considered to be of low birth weight (LBW). some infants are premature or preterm; borns at 37wks after conception or earlier. Other LBW infants are called small for gestantional age: they may be either preterm or full-term, but they weigh substantially less than is normal.
LBW have a higher risk of medical complications, neurosensory deficits, frequent illness, low IQ scores, and lower educational attainment.
causes of LBW:
- teratogens
- skyrocketing rate of twin,triplet, and other multiple births
long-term outcomes:
bad news - developmental problems and psychiatric issues
good news - majority of LBW children turn out quite well, negative effects of birth diminish, gain weight, develop to the normal range on most developmental measures.
intervention programmes:
(involves both time at hospital and after the infant returns home)
kangaroo care - a variant of the skin-to-skin care, parents used as incubators to help maintain infants skin temperature and promote breast feeding. been shown to decrease mortality, increase growth, breast feeding and attachment.
Field and her colleagues developed a special therapy involving massaging their baby and flexing arms and legs. this helps babies to be more active, alert, and to gain weight faster.
singing - improves health and calms parents fears.
problems with LBW infants:
- struggle to sleep
- struggle to wake up
- struggle to stay alert
- feeding schedules less regular
- more likely to be victims of parental child-abuse
helpful tips:
- learning about infant development
- seek social support
important points
- gains of intervention are relatively modest and diminish over time
- success of any intervention depends on the initial health status of the infant.
- interventions most beneficial to babies who are less tiny at birth which is a concern.
- cumulative risk: the more risks the infant endures, the lower the chances of a good outcome
Negative Outcomes at Birth
Multiple-Risk Models, Poverty as a Developmental Hazard and Resilience
the model states that the more risks a child faces, the more likely the child to suffer from a variety of developmental problems.
risk factors tend to occur together.
for example, a person who takes drugs is likely to be under a lot of stress, not eat and take vitamins, not earn a good income, seek prenatal care, have a strong support system, or take care of herself. this will likely to be carried on after birth resulting in the inability to take care of her child.
the more risk factors, the worse the potential outcomes.
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multiple risks are associated to Social Economic Status (SES).
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some children who are faced with multiple hazards do well (known as developmental resilience). often have two factors in their favor:
-certain personal characteristics, especially intelligence, responsiveness to others, and a sense of being capable of achieving their goals
-responsive care from someone
Understand the importance of experience and how it relates to plasticity of the brain
Plasticity of the brain - The importance of experience:
a) Experience-expectant plasticity
- the normal wiring of the brain occurs in part as a result of experiences that every human who inhabits any reasonably normal environment will have. the process not hardwired.
- Benefit? - so fewer genes needed to be dedicated to normal development and injury to certain areas can be taken over by other areas (so a function that would normally be lost, isn’t lost).
- Downside? - vulnerability when the expected experience does not happen, one example is cataract which is a defect of the eye or organ. the longer the cataract remains in place after birth, the more impaired the child’s visuals will be once it’s removed.
Sensitive period of brain plasticity:
the sensitive periods for cortical regions devoted to vision and other senses open in infancy. those for language and higher cognition open later, and never close entirely.
b)Experience-dependent plasticity
-Neural connections are created and reorganized throughout life as a function of an individual’s experiences.
-the more enriched environment we have leads to more complex brain outcomes.
- although if someone is in an enriched environment, how long must we have for it to have an impact (duration) and how much do we need to be exposed to the environment (dosage).
for example, if a musician practices too much, it can lead to harm.
