Developmental Psychology I: infancy and childhood part 3.1 Flashcards
Prenatal Development
There are three key periods in prenatal development:
Germinal - First 2 weeks - Planting the seed – Fertilisation to implantation.
Embryonic - Weeks 3–8 - Laying the structure – Major organs begin to form.
Fetal - Week 9 to birth - Growth and refinement – Everything gets bigger, more complex, and functional.
🧬 Germinal Period: Days 1–14 After Conception
🚀 Launch (Fertilisation):
The sperm meets the egg in the Fallopian tube, forming a zygote—a single-celled organism that contains all the genetic information needed to build a human.
🔁 Rapid Cell Division (Mitosis):
The zygote starts dividing into identical cells (called cleavage).
Imagine a single LEGO block duplicating itself into a growing pile—this pile becomes a blastocyst, a hollow ball of cells, by day 4–5.
🌰 Two Key Cell Groups Form Inside the Blastocyst:
Trophoblast (the outer shell): Becomes structures like the placenta, which will feed and protect the baby.
Analogy: Think of this as the spaceship’s life support systems.
Embryoblast (inner cell mass): This becomes the embryo—the future baby.
Analogy: This is the astronaut inside the ship.
🌱 Implantation (Day 7–14):
The blastocyst burrows into the uterus wall to start accessing nutrients.
Analogy: Like planting a seed in fertile soil—it needs contact with the nutrients in the ground (the mother’s blood supply).
However, implantation is risky—up to 50- 75% of zygotes fail to implant successfully, ending the pregnancy very early, often without the person knowing.
Ectopic Pregnancy (Complication) in germinal period
If implantation happens in the Fallopian tube instead of the uterus, this results in an ectopic pregnancy—a dangerous condition for the mother.
Order of germinal period?
1 Fertilisation The rocket is launched (sperm + egg → zygote)
2–3 Cleavage & Compaction The rocket builds compartments (cells multiply + stick tightly together)
4–5 Blastocyst forms The spacecraft inflates into a bubble with special rooms (trophoblast & embryoblast)
6–7 Zona hatching The outer shell breaks, allowing implantation (like a chick hatching)
7–10 Implantation Seed buries into soil (blastocyst embeds in uterus wall)
9–12 Differentiation Roles assigned—some cells become skin, others organs (crew members get jobs)
12–23 Disc formation & mesoderm spreading Layers form that will become tissues/organs (building floors of a complex facility)
The Embryonic Period
The embryonic period begins after implantation (~day 14) and continues until week 8 post-fertilization.
Think of this like constructing a house:
The germinal period was when you surveyed land and laid down a concrete foundation (zygote → blastocyst).
Now, in the embryonic period, you’re framing the house, setting up the plumbing and electricity — laying down the essential structures that will support all future growth.
The Early Protective Layers: Amnion, Yolk Sac, Chorion, Allantois in embryonic period
Imagine a spacesuit designed to protect and sustain an astronaut. The embryo builds its own little “spacesuit” made up of several layers and sacs:
🫧 Amnion → Like a Bubble Wrap + Thermostat
Forms a fluid-filled sac (amniotic fluid) around the embryo.
Acts like a shock absorber, maintaining temperature and cushioning the embryo.
Like floating in a warm bath inside a sealed room.
🥚 Yolk Sac → Portable Lunchbox
Produces early blood cells for the embryo until the embryo can produce its own.
Like bringing your own food before the kitchen (liver & spleen) is installed.
🧪 Allantois → Becomes the Umbilical Cord
Connects the embryo to its life support (mom).
Like the charger cable providing energy from the wall (mom) to the phone (embryo).
🪡 Chorion → Becomes the Placenta
The outermost layer that eventually becomes the interface with the mother.
Think of it as the Wi-Fi router that connects two systems — embryo and mother — without mixing their blood directly.
Placenta in embryonic period
a semi-permeable membrane embedded in the uterus wall that separates the mother from the embryo.
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Oxygen, carbon dioxide, sugars, proteins and fats can pass through placenta.
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Maternal blood entering the placenta carries oxygen (+ nutrients) to embryo via the umbilical cord.
Nutrients, oxygen, and waste are exchanged through a semi-permeable membrane (nothing mixes directly — like a customs checkpoint).
Umbilical cord acts as the cable for delivery and return.
🔄 Two-way exchange:
IN: oxygen, glucose, amino acids
OUT: carbon dioxide, urea, waste products
Embryoblast/Embryodisc Layers
The embryoblast, also called the embryonic disc, divides into 3 germ layers — the foundational “departments” that each build part of the human body.
🧱 The 3 Germ Layers – Like Departments in a Construction Team:
Ectoderm (outer layer)
→ Like the IT department: builds all the “wiring” and interface
Nervous system (brain, spinal cord)
Skin, hair, nails
Mesoderm (middle layer)
→ The engineering & structure crew
Muscles, bones
Cardiovascular system
Endoderm (inner layer)
→ The plumbing and internal systems
Digestive tract, lungs, liver, bladder
Formation of the Neural Tube (Week 3) in embryonic period
Here, a special region in the ectoderm called the primitive streak folds into the neural tube, which becomes the brain and spinal cord.
🔧 Analogy: It’s like folding a flat blueprint into a 3D structure — imagine rolling a piece of paper into a tube to make a tunnel (the neural tube). If this process goes wrong → neural tube defects (like spina bifida) can occur.
Body Plan Develops (Weeks 4–5)
🧠 Week 4
Head, eyes, nose, mouth begin forming.
Heartbeat begins — a primitive vessel starts pulsing. A minuscule blood vessel begins to pulsate, which will become the heart.
🧭 Direction of development:
Cephalocaudal (head to tail) – The brain develops before legs.
💪 Week 5
Limbs emerge: upper arms → forearms → fingers
Legs follow: thighs → knees → feet → toes
🧭 Direction:
Proximodistal (center to outer) – Inner organs first, then limbs. Internal to external
🧠 Week 6–8 in embryonic period
🧠 Week 6–8: Final Preparations
Fingers and toes separate.
Skeleton starts to form.
Brain rapidly develops — movements start (but not controlled yet). (however, deliberate movements are still not possible)
Liver and spleen take over red blood cell production.
Embryo reaches about 1 gram and 2.5 cm.
Neuropore closure failure
Failure of closure of the anterior neuropore during embryogenesis will lead to anencephaly, the failure of the brain and skull to develop
Fetal Period: Week 9 to Birth
At week 9, the developing individual is officially called a fetus.
By this point, most major organs and support structures are already laid down. The focus now shifts to growth, refinement, and activation.
🧬 7–8 Weeks: The “Indifferent Gonad” fetal period
If the embryo is male, the 23rd pair of chromosomes will consist of an X and a Y chromosome:
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A Y-chromosome gene (SRY gene) triggers the indifferent gonad to produce testes.
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If the embryo is female, no message is sent (because there is no Y-chromosome; females’ 23rd pair is XX) and ovaries are produced.
🧠 4–6 Months: Brain Boom fetal period
The brain increases 6x in size due to Neurogenesis = making tons of new neurons. Imagine installing miles of wiring in a building.
Synaptogenesis = creating connections between those wires — the switchboards and communication lines.
Development is proximo-distal — from the inner to outer brain:
hindbrain (pons, medulla & cerebellum) develops first, then the midbrain and then the forebrain (cortex + subcortical structures e.g. thalamus etc)
The cerebral hemispheres grow to cover other subcortical structures — like a dome growing over an older, central town.
🚨 5,5~6 Months: The Age of Viability in fetal period
This is the threshold (~22–24 weeks) where, with medical help, a fetus could potentially survive outside the womb.
Why? The central nervous system (CNS) starts regulating vital life functions like breathing and sucking.
However, this is only possible due to technology and healthcare conditions:
🍼 7–9 Months: The Final Countdown in fetal period
- The brain overproduces neurons and synapses — up to 25–75% will be pruned via apoptosis.
🔧 Think of this like sculpting a statue: you start with more clay than needed, then chip away the extra to reveal the form.
Unnecessary connections die off.
Useful ones are strengthened and reorganized for efficient neural circuitry.
- CNS-Mediated Coordination
Organs begin to act in concert — like an orchestra syncing under a conductor.
E.g., heart rate rises during activity and slows during rest. - Lung and Heart Maturation
Lungs practice breathing by “inhaling and exhaling amniotic fluid”.
Cardiovascular system finishes development — valves, veins, arteries all optimized. - Sensory & Emotional Connections
The fetus hears the mother’s voice and responds to rhythmic stimuli like singing or heartbeat.
Food flavors pass into amniotic fluid — a literal taste of the outside world. the fetus is considerably heavier (average of 3.4 kg at birth) and is able to move
Auditory communication in fetal period (7 months)
Auditory communication between mother and fetus is possible around 28 weeks (7 months) as hearing ability improves: the fetus may kick in response to loud noises or be comforted by the mother’s voice or rhythmic sounds (e.g., singing/music).
What is Apoptosis in fetal period
Apoptosis is the process of programmed cell death. It is used during early development to eliminate unwanted cells. The initial over-production of neurones ensures the fetus will have all the neurones it needs to function properly (rather than not having enough)
🧪 What Are Teratogens?
Teratogens are non-genetic agents that increase the risk of prenatal abnormalities or birth complications.
🔶 Non-genetic means they’re external—they’re not part of the baby’s DNA, but rather come from the environment.
🧪 Examples:
Drugs (prescription or recreational)
Viruses (like rubella or herpes)
Pollutants (like lead or mercury)
Radiation (think Chernobyl levels)
🔍 Important Note: Teratogens don’t affect all pregnancies equally—95% of pregnancies still result in normal births, and when problems do occur, they are often mild or reversible.
⏳ Sensitive-Period Principle
teratogen’s effect is most severe if it hits while an organ is forming.
📌 Most organs form during the embryonic period (3 to 8 weeks post-fertilization).
🧠 Examples of vulnerability:
Central Nervous System (CNS): 3–5 weeks
Heart: 3–6 weeks
Other organs: 5–9 weeks
🔬 So exposure to a teratogen before week 3 may not be harmful (implantation stage), but exposure between weeks 3–9 is high risk.
📊 Teratogen Timing Chart
🧠 CNS: vulnerable throughout entire pregnancy
❤️ Heart: mainly early (3–6 weeks)
🧬 Genitals, eyes, and ears: remain vulnerable even into the fetal period
🧠 Once Formed, Less Fragile – But Still Sensitive
Generally, formed organs are less susceptible.
But some parts (e.g., eyes, genitals, and nervous system) remain somewhat vulnerable all the way to birth.
👶 Individual Difference Principle. Why does the same drug harm some fetuses but not others?
🧬 Genetics plays a big role. Every embryo has different vulnerability thresholds, depending on both embryo/fetal and maternal genes.
Example:
Thalidomide: A drug that caused severe limb deformities—but only in certain pregnancies.
⚖️ Dosage Principle
Like poison, the dose makes the difference.
A small amount of alcohol might pass unnoticed.
Large doses? Fetal Alcohol Spectrum Disorders.
So:
Longer exposure = Higher risk
Greater quantity = More damage
One Teratogen, Many Effects | One Effect, Many Teratogens
🧬 One defect (e.g., growth restriction) can come from multiple teratogens (like smoking or alcohol).
🧬 One teratogen (e.g., syphilis) can cause multiple defects: eye, brain, heart damage.
Think of a single hammer that can shatter multiple parts of a clock—or multiple hammers hitting the same gear.
🕰️ Long-Term & Sleeper Effects
The long-term effects of a teratogen often depend on the quality of the post-natal environment:
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E.g., Babies prenatally exposed to opioids drugs can show normal development if they receive appropriate post-natal care (Hans & Jeremy, 2001 in Shaffer & Kipp, 2014).
🌙 Sleeper effect:
A teratogen lays dormant—then later manifests problems like:
Low sperm count in boys from prenatal alcohol exposure
Cognitive problems showing up only in school age
Teratogen type: Meds
Examples: Aspirin, barbiturates, thalidomide
Potential effect: Abortion, hemorrhages, malformations
_______________________
Teratogen type: Drugs
Examples: Cocaine, heroin, LSD, marijuana, alcohol, tobacco
Potential effect: Growth delays, withdrawal, irritability, premature birth
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Teratogen type: Infections
Examples: AIDS, herpes, syphilis, rubella, toxoplasmosis
Potential effect: Mental retardation, organ damage (e.g., eyes)
_______________________
Teratogen type: Environmental Hazards
Examples: Lead, mercury, radiation
Potential effect: Abortion, anemia, intellectual disability, growth retardation
Teratogens: Diseases
Some diseases cross the placental barrier—which usually acts like a gatekeeper—because the fetus’s immature immune system can’t defend itself (it can’t yet make antibodies, the “soldiers” that fight infection).
Teratogens: Diseases 🧫 Rubella (German Measles)
A seemingly “mild” illness for adults (fever, headache) can be catastrophic if caught during the first 3 to 4 months of pregnancy:
First 8 weeks: ⚠️ High risk of blindness and cardiac abnormalities.
6–13 weeks: ⚠️ High risk of deafness.
Any time in first 3–4 months: ⚠️ High risk of mental retardation.
😷 Teratogens: Diseases
Sexually transmitted diseases are especially dangerous because they often get a direct line into the developing system.
🦠 Syphilis: It causes the most damage during middle and later stages of pregnancy. The bacteria (spirochetes) that cause it can’t pass through the placental barrier until the 18th week.
After this point, it can cause:
Miscarriage
Or damage to: eyes, ears, bones, heart, and brain
🦠 Genital Herpes (Herpes Simplex):
The virus can cross the placental barrier, but most often infects the baby during birth, when it comes into contact with the mother’s genitals.
This infection is lethal in 30% of infected newborns and can cause:
Blindness
Mental retardation
⚠️ Pregnant women with active herpes are advised to undergo cesarean delivery to avoid infecting the baby during natural birth
💊 Teratogens: Drugs – Thalidomide
This is one of the most tragic and famous teratogenic disasters in history.
In the 1960s, a West German company sold thalidomide as a mild tranquilizer for nausea during early pregnancy.
The drug was presumed to be safe as it had no bad effects on rat mothers or their offspring.
However: Taking thalidomide during the first 2 months of pregnancy led to:
Severe birth defects, depending on the exact timing it was taken.
📅 Thalidomide Timing Effects
Timing was everything. Here’s how the day post-fertilization shaped the consequences:
~21st day: 🧏♂️ No ears
~25–27th day: 🦾 Deformed arms or no arms
~28–36th day: 🦿 Deformed legs or no legs
After ~40th day: ✅ Baby usually unaffected
Importantly, not all mothers were affected, suggesting:
Not all individuals respond the same way to teratogens
👉 This highlights genetic differences, like how some people can eat peanuts safely, while others go into shock. Genes modulate sensitivity to these threats.
🍷 Teratogens: Drugs
Alcohol interferes with placental function, cutting off the “supply chain” (oxygen and nutrients) like a bridge being closed during construction.
Even a moderate amount (one glass of wine or beer) can be risky.
The most severe risks come from binge drinking:
Defined here as 5+ drinks per session.
🧠 Fetal Alcohol Syndrome
This is one of the most common alcohol-related birth disorders.
Children with Fetal Alcohol Syndrome (FAS) may show:
Microcephaly (small head)!!!!!!!
Deformed heart, limbs, joints, face
Poor body growth
Hyperactivity, seizures, tremors
Below average intelligence
Poor motor skills, attention deficits
⚠️ Critically, there is:
No well-defined sensitive period for alcohol—it can do harm at any time during pregnancy.!!!!!!!
🚬 Teratogens: Drugs – Cigarette Smoking
When a mother smokes, nicotine and carbon monoxide enter the baby’s bloodstream via the placenta.
These substances interfere with the placenta’s oxygen and nutrient delivery system.
In fact, nicotine levels in the baby’s blood can be 15% higher than in the mother’s!
👶 Effects of Smoking:
Smoking during pregnancy is linked to:
Cleft lip (± cleft palate)
Abnormal lung function, hypertension
Increased miscarriage and infant death
Low birth weight and slower growth
Nutrition & Diet on the fetus
Poor prenatal nutrition = fewer raw materials for construction.
Ideal diet: high protein, high calorie
Mothers should gain 1–2.3 kg in first 3 months, then 45g/week.
Severe malnutrition has different effects depending on timing:
1st trimester: Can disrupt spinal cord formation → 🛑 miscarriage
3rd trimester: Can cause underweight, under-sized head, and even mortality in the first year.
🌿 Vitamins and Neural Development (Slide 49)
Magnesium & Zinc help the placenta work better and reduce birth complications.
Folic acid (found in fruits, liver, beans, tuna, greens):
Helps develop the neural tube—the foundation of the spinal cord and brain
Must be taken in the first 8 weeks
Without it, serious neural defects can occur:
Spina bifida: Spinal cord bulges through a gap in the spine.!!!!!
Anencephaly: The brain and cranium fail to develop.!!!!
Spina bifida and Anencephaly
Spina bifida: Spinal cord bulges through a gap in the spine.!!!!!
Anencephaly: The brain and cranium fail to develop.!!!!
Maternal Age
✅ Safe age range
The safest age for pregnancy appears to be between 16 and 35 years of age (Dollberg et al., 1996, in Shaffer & Kipp, 2014).
👶🏽 Mothers younger than 16
More likely to deliver prematurely and have under-weight babies.
However, this risk is more related to the socioeconomic conditions of the mother rather than her physiology.
Teenage mothers tend to come from economically impoverished environments — characterized by poor nutrition, high stress, and minimal prenatal care.
Young mothers (< 16 years) are not usually at risk when they receive support and adequate prenatal care.
👵🏼 Pregnancy older than 35 years
👵🏼 Pregnancy older than 35 years
Associated with different risk factors compared to younger mothers.
Increased risk of miscarriage, partly due to a higher likelihood of chromosome abnormalities.
⚠️ Despite the elevated risk, the vast majority of pregnant women older than 35 have normal pregnancies and healthy babies
Maternal Stress
🧠 Impact on fetus
The emotional state of pregnant mothers influences the physiological state of the fetus:
Increased stress during a difficult cognitive task has been associated with
decreased heart rate and motor activity in the fetus (DiPietro et al., 2004).
However, temporary fluctuations in emotional/stress responses are not harmful for the developing fetus.
🔹 Maternal Stress (continued)
🚨 Chronic and Severe Stress
Linked with developmental abnormalities:
Reduced prenatal growth, premature delivery and low birth weight (Weerth et al., 2003 in Shaffer & Kipp, 2014)
Irritable temperament of newborn, irregular sleeping and feeding habits
(Vaughn et al., 1997 in Shaffer & Kipp, 2014)
Proposed mechanism (Suggested!!!!!!): Stress hormones like cortisol may divert blood flow toward large muscles (in the mother), reducing oxygen and nutrient supply to the fetus.
What is Amniocentesis in testing?
Prenatal screening technique to detect chromosome abnormalities, often used in at-risk women (e.g., age > 35).
Involves insertion of a large, hollow needle into the abdomen to sample amniotic fluid.
Fetal cells in the fluid are tested for:
Down’s syndrome (trisomy 21 – third copy of chromosome 21)
Cystic fibrosis, hemophilia, etc.
⚠️ Disadvantages:
Cannot be performed until 11–14 weeks post-fertilisation (due to low amniotic fluid).
Analysis takes up to 2 weeks, reducing time available for intervention.
🔹 Chorionic Villus Sampling (CVS)
A catheter (thin tube) is inserted through vagina/cervix, or a needle through abdomen.
Samples fetal cells from the chorion (membrane surrounding fetus).
Subjected to same tests as amniocentesis, but can be done earlier:
During 8th–9th week
Results available within 24 hours
⚠️ Risk of miscarriage:
Much higher than amniocentesis:
1/50 vs 1/150
Thus, recommended only for very high-risk pregnancies.
🔹 Ultrasound (sonar) imaging
A very safe, common diagnostic tool.
Most useful after 14th week of pregnancy.
Helps detect:
Gross abnormalities, multiple pregnancies, sex of baby
Also guides amniocentesis and CVS
⚠️ Limitation:
Only provides outline/surface of fetus, not suitable for deeper or more invasive analysis.
What is Gross abnormalities?
Observations or examinations made with the naked eye
